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Es wurde die Wirkung einer chronischen Bleivergiftung auf die Arginasesynthese in der Leber und die Arginaseaktivitat menschlicher Blutkorperchen untersucht. Die Synthese sowie die Aktivitat der Arginase werden durch Blei stark gehemmt.

Neural regulation of muscle cholinesterase (ChE) is well documented, although the mechanisms remain unresolved. We examined the enzyme activity changes in nerve and muscle after nerve transection, as they relate to nerve stump length and synthesis of ChE in denervated muscle. Changes in ChE activity were determined in rat skeletal muscles and sciatic nerve after nerve transection and after irreversible inhibition with paraoxon. The results showed that the decrease in enzyme activity in muscle was unrelated to the length of nerve stump. It was also shown that denervated muscle was capable of enzyme synthesis. Enzyme activity in nerve segments distal to transections decreased earlier than in denervated muscle and ChE in these samples of nerve was less sensitive to paraoxon. Although the nerve stump length and decrease in muscle enzyme activity were unrelated, the results suggest that the earlier decrease in enzyme activity in transected nerve may be related to the loss of biochemically determined muscle ChE.

Mustard seedlings were irradiated with continuous far-red light either with or without far-red preirradiation for between 6 and 44 h. The preirradiation increases the rate of light-mediated phenylalanine ammonia-lyase (EC 4.3.1.5) accumulation in the cotyledons up to 5-fold but does not eliminate the apparent lag-phase of induction which lasts between 30 and 60 min, both with and without a preirradiation. No differential effect of inhibitors presumed to be acting close to gene transcription was observed for plants, whether given a preirradiation or not. These results do not support the notion that two different induction mechanisms are involved in the action of phytochrome on phenylalanine ammonia-lyase synthesis during primary and secondary irradiation. There was however a strong promotive effect of preirradiation on P fr-mediated enzyme accumulation which can be explained by an elevated level of the rate of enzyme synthesis left over from the previous light treatment and a transient increase in the capacity of the system to increase the rate of enzyme synthesis in response to active phytochrome.

Summary Tetrahymena pyriformis GL-I were synchronized by three different techniques and nucleoside phosphotransferase activity measured through the different cell cycles obtained. In cells that were starved and then refed, activity did not increase until 75 min after refeeding. This increase in activity occurred well before nuclear DNA synthesis and was not blocked by hydroxyurea. In cells synchronized by the induction technique of one heat shock per generation and the selection technique of differential density labelling, enzyme activity increased continuously over the cell cycle but did not double. However, during early logarithmic growth nucleoside phosphotransferase activity more than doubled over one cell cycle time while late in log growth phase less than a doubling was observed. Cycloheximide and mixed extract experiments suggest that the patterns of activity observed reflect the patterns of enzyme synthesis. These results are discussed with respect to the pattern of activity observed for thymidine kinase in other organisms.

Two mesophilic fungal strains, identified as Humicola grisea were isolated from forest soil. Strain Humicola grisea Fb digested a variety of lignocellulosic growth substrates. The amount of cellulase enzymes induced on processed cellulose was higher than on lignocellulose. This strain exhibited high carboxymethylcellulase [ endo-1,4 -β- d - glucanase , ( 1,4 -( 1,3:1,4 )-β- d - glucan 4-glucano hydrolase, EC 3.2.1.4 )], filter paper degrading activity, and Avicelase activity in cultures on cellulose powder, Avicel and filter paper. The culture filtrate of cellulose powder-grown H. grisea Fb hydrolysed filter paper to the extent of 8% and carboxymethylcellulose and Avicel to 33% and 6.5% in 3 h respectively. The carboxymethylcellulase activity in the culture filtrate ( 7.41 U ml −1 ) was adsorbed onto Avicel to the extent of 22%. The carboxymethylcellulase activity in the culture filtrate was optimally active at 50°C and pH 5.0 .

PERSPECTIVES AND SUMMARY 1 33 RIBONUCLEOTIDE REDUCTASE FROM ES CHERICHIA COLI 136 Structural Aspects 136 Reaction Mechanism ....... .. ..... ......... ..... ... ...... ... ... ... ....... .. ..... .. ... ..... ... . 138 Allosteric Control 1 39 Hydrogen Transport System 140 RIBONUCLEOTIDE REDUCING SYSTEMS INDUCED BY BACTERIOPHAGES .... . . . . . . . . .. ... .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 RIBONUCLEOTIDE REDUCTASE FROM LACTOBACILLUS LEICHMANNII ... . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . ... . . ... . . . . ... . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 144 Structural Aspects ... .. ....... .... . . .. . ... . . . . ... . . . . . . . . . . 144 Reaction Mechanism 145 Allosteric Regulation ..... .. . .. .. . .. .. .. ...... ........ ........ ... ... ... ........ ..... ..... ....... ... . ....... 146 OTHER B12-DEPENDENT REDUCTASES.... .. . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 MAMMALIAN RIBONUCLEOTIDE REDUCTASE . . .. . .. . . . ... . .. . .. . . . . . . .... . . . . . . . .. . . . . . . .. 147 Structural Aspects and Reaction Mechanism 147 Allosteric Regulation . .. ... ....... .. .. . ...... ........ . ..... ..... ..... ... ... . ..... ..... . .. ... . .. . . .. . .. .. ..... .. . .. .. ... 149 Hydrogen Donor System .. ..... .. . ... 150 RIBONUCLEOTIDE REDUCTION AND DNA SyNTHESIS 1 5 1 Correlation o f I n Vitro and I n Vivo Activities 151 Regulation of Enzyme Synthesis 154 Deoxyribonucleotide Pools ... ..... .. .. ..... ........ ... ... .. ... .. . .. .. . ... ... ... ... ... ... .. . .. .. .. . .. .. ..... ... . . . ... 154

The rates of synthesis and degradation of arginosuccinate synthetase in rat liver under various dietary conditions were determined. The relative rate of the enzyme synthesis in the livers of rats fed on 70% casein diet was 4.0 times greater than that for rats fed on 5% casein diet. The rate constants of degradation (Kd of argininosuccinate synthetase were estimated to be 0.15 and 0.16 day-1 under 70% and 5% casein feeding, respectively. When the dietary conditions were changed acutely from 70% to 5% casein diet or vice versa, the rates of the enzyme synthesis decreased or increased, respectively, and the rates of enzyme degradation were also affected. The change from 5% to 70% casein diet caused a transient decrease in the rate of degradation. After the enzyme activity had achieved a new steady-state level, the enzyme degradation proceeded at the normal steady rate. On the other hand, the change from 70% to 5% casein diet caused a transient increase in the rate of degradation. Thus, the only factor regulating the amount of enzyme in rat liver is the rate of enzyme synthesis under the steady-state conditions. However, the rates of both enzyme synthesis and degradation are involved in the regulation of the amount of enzyme during dietary transition.

During the last few years, the method of DNA directed enzyme synthesis in vitro has become a powerful tool in the study of gene expression.

Following axonal injury, there is a 45% reduction in the amount of DBH in the neurons of the locus coeruleus (LC). To determine if this is due to reduced enzyme synthesis, 3H-leucine was infused into the IVth ventricle of control and lesioned rats. The relative rate of DBH synthesis (3H-DBH/3H-total protein) was reduced 40% in the LC of lesioned rats as compared to controls, indicating a selective reduction in DBH synthesis. During axonal regeneration, there may be a selective reordering of protein synthesis favoring synthesis of proteins for axonal regeneration rather than neurotransmission.

When fruits ripen they undergo major changes in composition which affect their attractiveness, storage life and nutritional value. This is a consequence of alterations in the physiological and biochemical processes occurring in the cells of the fruit. A list of some of the major changes that occur in tomatoes is given below. Similar changes occur in many other types of fruits.

We have used computer analysis of a modified version of a model oscillator ( Goodwin, 1965 ) to simulate phase response curves such as are obtained in circadian systems. In accordance with recent working hypotheses of the mechanism of the circadian clock, the model consists of three components: an enzyme, its product and a translational inhibitor whose activity depends on the translational product, which in turn determines the rate of enzyme synthesis. The oscillations of the three variables were perturbed with single impulses applied at different phases. The phase and amplitude of the resulting curves depended on the variable affected, the sign of the perturbing stimulus and its strength. The consequences of these results for interpreting the molecular mechanism of circadian clocks on the basis of phase response curves to various treatments are discussed.

SummaryGlucocorticoid antagonizing factor, GAF, from cultured macrophages and in serum of endotoxemic mice blocks cortisol induction of phosphoenolpyruvate carboxy-kinase in Reuber H35 rat hepatoma cells. Direct endotoxin treatment of hepatoma cells was not inhibitory. Dibutyryl cyclic AMP induced enzyme synthesis and Cortisol induced synthesis of tyrosine aminotransferase were not affected by GAF. Phosphoenolpyruvate carboxykinase induction by cortisol in hepatoma cells could be used to quantitate levels of GAF in serum. This assay system is ten times more sensitive than in vivo assays for GAF and it can also be used to titrate samples for comparing GAF responses.

The single feature which probably characterizes all aging populations is a progressive impairment in the ability to adapt to environmental change. Adaptation may be expressed at a biochemical level by modifications in the rates of synthesis and degradation of enzymes, as well as by alterations in physiological activities. Thus, it was gratifying to discover that the susceptibility of at least certain enzymes to the regulation of their activities is impaired during aging. The present chapter will review the effects of aging on enzyme regulation; discuss the possible roles of alterations in appropriate hormonal interactions and hepatic gene expression; and suggest the manner in which these observations may provide the basis for eventual comprehension of the underlying biochemical mechanisms responsible for the physiological decline which accompanies old age.

Extracellular proteolytic enzymes of microbial origin are often employed in various branches of industry. The neutral and alkaline proteinases of Bacillus subtilis belong to the most extensively used enzymes. However, these proteinases are also of great significance from the theoretical point of view. They are synthesized during the post-exponential and stationary phases of growth and the control of their formation is somehow related to sporogenesis [1,2].

Diets containing raw soya-beans (RSD) when fed ad libitum cause reduction in growth rate and food utilization, enlargement of the pancreas and increase of its enzyme synthesis. A single meal of raw soya-beans with corn (1 : 9), tube-fed to geese, caused about 90% mortality, while geese, tube-fed with corn alone, did not show any negative response. No mortality occured when geese were fed a similar diet ad libitum. Two-week old chicks were fed ad libitum or by tube, twice a day, similar amounts of RSD or heated soya-bean diet (HSD). While the chicks tube-fed HSD behaved similarly to those feeding freely, the chicks tube-fed RSD collapsed after one week. The thymus and bursa of fabricii were atrophied in the RSD tube-fed chicks. Diets containing increasing amounts of raw soya-bean meal (0, 20%, 42%, and 80%) were fed freely to weanling rats or as one 4 h meal per day. All the rats fed the 4 h meal containing either 42% or 80% raw soya-bean meal died within 3 days; all the others survived. The rats were trained to meal-feeding by gradual reduction of their access to food. The negative effects of the RSD, i.e. reduced food intake and body weight gain, pancreas enlargement, were much more pronounced in the meal-fed rats than in those fed ad libitum. The differences increased by increasing dietary trypsin inhibitor (TI) (raw soya-bean meal).

A revised enzyme synthesis rate expression for cybernetic models of bacterial growth is presented. The rate expression, which is comprised of inducible and constitutive contributions, provides for a basal enzyme level that is necessary to predict certain types of commonly observed continuous culture transients. The response of a continuous culture to a step change in feed stream composition is simulated using both the old and new formulations, and the ramifications for the “matching-law” formulation are discussed.

Publisher Summary This chapter discusses the methods used for the analysis of enzyme synthesis and degradation in animal tissues. It is well established that the amount of an enzyme present in animal tissues results from opposing processes of continual synthesis and degradation and that either process can be altered by hormonal, nutritional, developmental, or genetic factors. There are a number of methods to assess the contributions of altered synthesis and/or degradation to changes in enzyme (protein) level, including immunologic methods, uses of tracer techniques, and analysis of time courses of changes in enzyme levels. Each method embodies certain assumptions, as well as limitations, and unambiguous conclusions generally can be made only when independent estimates of the rates of synthesis and degradation are made and when more than one method is employed. Tracer techniques are used most commonly for estimating degradation rates. Although such techniques may seem direct, they are full of pitfalls that can result in ambiguous results. Isotope methods can be divided into two general techniques: (1) single isotope administration and (2) continuous isotope administration. The use of reutilizable isotopes in pulse-decay experiments, although commonly employed, has severe limitation(s) in interpretation. They do not, by themselves, provide measures of true half-lives of enzymes. They can, under suitable conditions, provide information on whether two or more proteins in a similar tissue have different rates of turnover.

Publisher Summary The comparative survey of induction mechanisms used by different bacterial genera to govern the synthesis of enzymes for a single pathway can give insight into some of the factors that contributed to the selection of particular compounds as inducers and to the evolution of patterns of inductive control. This chapter presents different types of inductive control and discusses the regulation of inducer levels. Inductive control evolves through the modification of preexisting genetic material. The chapter discusses β-ketoadipate pathway, which is a multistep route for the dissimilation of aromatic compounds. It highlights the regulation of β-ketoadipate pathway in two bacterial species, Acinetobacter calcoaceticus and Pseudomonas putida . This provides a background for tracing the development of concepts about four evolutionary factors that influence the evolution of induction mechanisms: (1) the economy of enzyme synthesis, (2) unification of inductive control, (3) the preexisting genetic material from which genes evolved, and 4) the role of nutritional opportunities in the natural environment in the selection of organisms with specific patterns of induction.

The action of somatostatin on intestinal alkaline phosphatase activity (IAP) in the duodenal juice was examined in 22 subjects undergoing diagnostic secretin-CCK-PZ-tests. Under continuous secretin-CCK-PZ-stimulation there is an increase of IAP which is followed by a period of exhaustion after 1 h of stimulation. The intravenous administration of somatostatin induces a distinct inhibition of IAP which cannot be due to the exhaustion of the enzyme synthesis. As there is a functional relationship between fat absorption and alkaline phosphatase, it is suggested that this inhibition of IAP is one of the mechanisms of the somatostatin-induced inhibition of intestinal fat absorption.

The period of oscillation in a negative feedback loop is shown to be much longer than the half-life of the most stable element of the loop. This places a severe constraint on the theory that stepwise increases in enzyme activity are caused by periodic repression of enzyme synthesis.

Until fairly recently, the main emphasis in neurobiological research was concentrated on morphological features of neuronal systems and electrical phenomena of neuronal activity. Biochemical investigations were mainly confined to static-descriptive approaches, particularly those concerning the macromolecular constituents of neurons. The neurons were thought to act as stable electronic components designed to generate, transmit, and modulate electrical impulses. This attitude regarding the interpretation of neuronal activity and neuronal interaction prompted a comparison of neuronal systems with computers. However, the basic difference between a computer and an integrated neuronal system such as the mammalian brain is the “plasticity” of the latter, i.e., its capability to adapt to changing functional requirements (Giacobini, 1970). Although the general arrangement of neurons and their “wiring” are genetically determined, there is a relatively wide range of variability available for modifications according to the use of the neuronal pathways and connections. The ability of neurons to undergo “plastic reactions” is reflected not only by biochemically detectable changes in their macromolecular composition but even changes in their morphology (Cragg, 1972; Horn et al., 1973). These function-dependent biochemical and structural changes do not appear to have an analogue in contemporary electronic systems.

INTRODUCTION THE MULTIPLE BIOLOGICAL FUNCTIONS OF tRNA . tRNA Cycle in Protein Synthesis . tRNA and the Regulation of Enzyme Synthesis . Aminoacyl-tRNA Transferases . tRNA Participation in Polynucleotide Synthesis . tRNA as an Enzyme Inhibitor . tRNA Changes in Cells .

Administration of endotoxin to adult rats increases lung Cu,Zn superoxide activity after 72 h of exposure to greater than 95% O2. The increased activity is brought about mainly by a faster rate of Cu,Zn superoxide dismutase synthesis; rats treated with endotoxin but not exposed to hyperoxia do not exhibit these findings (Hass, Frank, and Massaro, J. Biol. Chem. 257: 9379-9383, 1982). We now report that 48 h after treatment of adult rats with endotoxin there was a decreased rate of Cu,Zn superoxide dismutase synthesis by lung slices from air- and O2- exposed rats, although, in both groups, the lung concentration of Cu,Zn superoxide dismutase mRNA was increased approximately 45%. Exposure of endotoxin-treated rats to greater than 95% O2 or air for an additional 24 h (72 h all told) resulted in continued elevation of Cu,Zn superoxide dismutase mRNA only in lungs of O2- exposed rats. In vitro exposure of lung slices from air-breathing saline- or endotoxin-treated rats to 95% O2 for 6 h led to an increased rate of Cu,Zn superoxide dismutase synthesis only in slices from endotoxin-treated rats. We conclude that endotoxin treatment leads to an increased concentration of Cu,Zn superoxide dismutase mRNA in rat lungs, but a sustained elevation of the mRNA, and its translation into an increased rate of Cu,Zn superoxide dismutase synthesis requires exposure of the lung to hyperoxia.

Incorporation of intravenous 75Se-methionine into duodenal juice proteins during pancreatic stimulation was measured as an index of pancreatic enzyme synthesis rates in 12 patients with a normal pancreatogram and in 6 with mild chronic pancreatitis. Isotope incorporation was significantly greater in subjects with mild chronic pancreatitis than in those with a normal pancreatogram. Thus in most patients in whom pancreatography demonstrates the characteristic radiological features of ‘mild chronic pancreatitis’ pancreatic acinar function is abnormal. The coexistence of morphological and functional abnormality implies that such patients do have chronic pancreatitis.

The effect of dibutyryl cyclic AMP and theophylline on lipoprotein lipase secretion was investigated after a 24 h pretreatment of human monocyte-derived macrophages. Both the effectors decreased in a dose-dependent manner the enzyme activity recovered in the culture medium. The decrease in lipoprotein lipase activity appeared to be related to reduced enzyme synthesis without apparent modification of its stability and half-life and was conversely associated with an increase of lysosomal acid hydrolase activities. This effect was reversible on removal of the nucleotide. The present findings suggest that cyclic AMP may play a role in lipoprotein lipase expression in human macrophages and therefore may participate in the regulation of lipoprotein uptake by these cells, which are strongly implicated in the atherogenic process.

To live in a changing environment requires the ability to adapt. In its day to day existence an animal encounters variation in environmental stresses, in activity requirements, and in type and amount of food intake. To meet an animal’s needs in its current situation, the flow of nutrients through its metabolic pathways must be subject to regulation. One of the primary means of controlling the disposition of nutrients is the regulation of enzyme activities.

Wild-type cells of E. coli K-12 showed increasing U.V. resistance if they were X-irradiated and incubated at 37 degrees C in growth medium before the U.V. exposure. Development of higher U.V. resistance could be inhibited by incubating the X-irradiated cells either at temperatures below 15 degrees C, or in the presence of 0.01 M KCN. Nitrofurantoin (NF), which was recently found specifically to inhibit inducible enzyme synthesis, had only a transient inhibitory effect on X-ray-induced U.V. resistance. Cells grown in glucose medium showed less inhibition by NF of X-radiation-induced resistance to U.V.-radiation than did cells grown in glycerol, or in glucose medium with added cyclic AMP. It is suggested that X-ray-induced U.V. resistance requires active cellular metabolism, but it is not subject to catabolite repression. The following hypothesis is offered to explain the action of NF: Under de-repressed conditions (without catabolite repression by glucose) nitrofurantoin could counteract the radiation-induced inhibition of a repair inhibitor (such as post-irradiation DNA degradation).

Light has been shown to modulate the activity of an extensive range of plant enzymes. In the case of some photosynthetic enzymes changes in activity are directly related to the increase in reductive power produced during the light reactions of photosynthesisl; however this system lies outside our remit and discussion here will be confined to the modulation of enzyme activities by photoreceptors other than the photosynthetic pigments. Most information is available for phytochrome-regulated enzymes but there is also some useful data involving blue and UV light. However before analysis of the detailed information that is currently available it is worthwhile considering a few general points concerning enzyme activities and photomorphogenesis.

The problems of enzyme production are examined in the light of molecular biological events. an understanding of the dynamics of protein synthesis that occur during transient growth are reviewed to provide insight into the potentials and the limitations of differential enzyme synthesis.

The synthesis of β-galactosidase (EC 3.2.1.23: β-D-galactoside galactohydrolase) in Escherichia coli is repressed as a result of infection with single-stranded DNA phage OX174. An amber mutant in OX174 cistron A, which codes for two proteins, does not inhibit the enzyme synthesis while amber mutants in all other genes do cause repression. A mutant near the amino-terminal end of cistron A, which produces the small 35,000 molecular weight cistron A polypeptide, also inhibits the synthesis of β-galactosidase. Inhibition is also observed in an Escherichia coli rep mutant which does not support the replication of replicative-form DNA. Exogenous nucleotide bases and cyclic 3′,5′-adenosine monophosphate (cyclic AMP) do not have any effect on the degree of repression.

This chapter covers a period of approximately 200 years that begins around 1780. The concept of “the bacterium” changed and developed during this time, and strong and often conflicting views were held by the leading scientists of the day. Leeuwenhoek’s (1677) animalcules (described in his famous letter of 1676) are now considered to have included bacteria, and although at the beginning of the period under review there were those who thought that small living organisms might cause disease and bring about fermentations, there was no firm scientific evidence for either of these activities. The methods of the natural scientists, particularly the botanists, were used to observe and describe the teeming life that could be seen with the help of the improved microscopes. From a time when all very small organisms, including worms, protozoa, microfungi, and bacteria were regarded as similar creatures to be observed and described, we can trace an increasing awareness of the special attributes of bacteria. It took many years to settle the two major controversies over whether bacteria arose by spontaneous generation and whether fermentation was carried out by living organisms. The supporters of the spontaneous-generation origin of microorganisms had arguments of common sense to sustain them, together with weak experimental technique. Until good methods for sterilization were available, it was difficult to refute their claims, and until the heat resistance of bacterial spores had been recognized, it was difficult to ensure that sterilization methods were adequate. The most vociferous supporters of spontaneous generation were mainly biologists, and a few chemists, while the main opposition to the concept of the microbiological basis of fermentation came from the leading organic chemists. Berzelius, Liebig, and Wohler thought that fermentation and putrefaction were due to the chemical decomposition of organic matter and poured scorn on the conclusions of Schwann, and later Pasteur, that fermentation did not occur in solutions that had been sterilized by heating unless some living organisms had been added. They did not deny that yeasts, or other organisms, were present in fermentations, but considered them to be casual rather than causal.

There is considerable evidence that the synthesis and degradation of proteins is a dynamic process which governs the steady-state level of enzymes in the cell. Although a great deal is known about the factors that regulate the rates of enzyme synthesis, relatively little is known about the mechanism involved in the regulation of enzyme degradation. It is known that various enzymes are degraded at different rates which are determined in part by undefined nutritional factors and that degradation is dependent upon a supply of metabolic energy (ATP) (Goldberg and St. John 1976; Holzer and Heinrich 1980). To gain more insight in to this problem, studies in our laboratory (Fulks 1977; Maurizi 1980; Oliver and Stadtman 1980) have been directed toward the development of cell-free enzyme preparations that catalyze the selective proteolysis of individual enzymes.

This lecture deals predominantly with the photoregulation of enzyme levels in plants by the photochromic proteinaceous photoreceptor, phytochrome. While there are claims that photocontrol of enzymes (enzyme synthesis, degradation, and activation) may be mediated by light absorption in other pigments as well (e.g. photo-synthetic pigments [1]) , the emphasis on phytochrome is justified for two reasons: firstly, phytochrome is the most important molecule in higher plants for the detection of photosignals from the environment and for making use of this information to regulate the orderly development of the living system; secondly, detailed knowledge of the molecular mechanisms through which phytochrome exerts its control over the development of higher plants may serve as a useful model for understanding the control of development in general, i.e. the control of gene expression during development.

It is perhaps self-evident that the metabolism of micro-organisms, and indeed of all living organisms, is under strict in vivo control. Micro-organisms show a remarkable reproducibility in structure and composition, a reproducibility that is maintained even when they are grown in media of widely different chemical composition. Moreover, rapidly growing micro-organisms usually accumulate, either intracellularly or in the environment, only very small quantities of compounds that could be used in synthesis of new cell material, which indicates that there is extremely little wastage during cell metabolism. There are many other examples that could be quoted to show the remarkable degree of control and economy that operates in the metabolism of micro-organisms.

It is a truism of biology that all the parts must fit together to make a viable organism. In terms of cellular metabolic activities this means that the rates at which enzymes act must be compatible with one another, and the appropriate amounts of enzymes must be synthesized at the time they are required. The regulatory systems have evolved to do this.

Wild strain of Aspergillus terreus is very good producer of beta-glucosidase. It produces 15 nkat/mL (0.9 IU/mL) of extraceLlular beta-glucosidase at pH 5.0. The medium pH level strongly affects the production and binding of beta-glucosidase on the cells and on residual cellulose. At pH 4.0 the rate of enzyme synthesis and the level of total activity is highest but 60-75% of this activity is bound. At higher pH levels the enzyme is mainly released to the medium.

The regulation of GAL1 RNA and enzyme synthesis has been investigated in Saccharomyces cerevisiae. We have shown that the induction of GAL10 and GAL1 RNAs is coordinate. GAL1 RNA transcripts appear within 4.5 to 6 min and galactokinase synthesis within 6 to 9 min. Steady-state RNA levels were reached within 50 min and the steady-state rate of galactokinase enzyme synthesis within 40–50 min. From these kinetic studies, the initial induction of GAL1 enzyme activity is apparently under transcriptional control. In addition, during early induction, two galactokinase enzyme activities were detected; a major stable form and a minor unstable form.

This chapter provides an overview of the molecular mechanism of phytochrome action, the processes through which phytochrome regulates development, and function of phytochrome in plants growing in the natural environment. The great plurality and diversity of phytochrome-controlled biochemical changes pose major difficulties for the construction of a unified hypothesis of the phytochrome control of development. As yet, there is no direct evidence for the regulation of mRNA synthesis by phytochrome. Therefore, it is no longer possible to hold to the view that phytochrome controls development by regulating gene expression at one locus only. There are basically two general hypotheses to account for the manifold and rapid effects of phytochrome on cell metabolism and development. The first proposes that one or more second messengers act as intermediaries between the single primary action of phytochrome at the membrane, and its ultimate effects on enzyme synthesis and activity. The alternative view is that more than one primary reaction of phytochrome is possible, depending perhaps on its location within the cell.

Summary: The regulation of the synthesis of the first three enzymes of the quinate-shikimate catabolic pathway in Neurospora crassa has been studied. Induction of these enzymes is promoted efficiently by quinate and less so by 5-dehydroquinate and/or 5-dehydroshikimate. Shikimate has little or no inducing ability. The kinetics and steady-state rates of synthesis of the three catabolic enzymes have been examined. It is suggested that quinate-shikimate dehydrogenase, catabolic dehydro-quinase, and 5-dehydroshikimate dehydrase are regulated coordinately.

Based on the consideration that normal metabolic processes depend upon the activity of key enzymes (and membrane carriers) as modulated by regulatory factors (hormones, diet, endogenous compounds, age, physical activity, environmental agents), metabolic disorders might be classified into two groups: (I) defects in enzyme synthesis, leading to enzyme deficiency (classical inborn errors of metabolism) or to qualitative (structural) enzyme alterations (entailing unresponsiveness to regulation), in the presence of normal regulatory factors; (II) defects in enzyme regulation, which include metabolic syndromes such as diabetes mellitus, obesity and hyperlipoproteinemias (other than type I), and are due to changes in enzyme activities caused by alterations in regulatory factor(s) (secondary to various causes), in the presence of normally responsive enzymes.

Mutations which affect the regulation of Neurospora repressible alkaline phosphatase do so by altering the rate of de novo alkaline phosphatase synthesis. In regulatory mutants the rate of alkaline phosphatase polypeptide synthesis can vary over a 1000-fold range. Following transfer to phosphate-free medium, the wild-type cell is capable of increasing the rate of synthesis of alkaline phosphatase molecules within 30–45 min.

In this paper we consider the behavior of solutions to the differential-difference equation $$dx(t)/dt = a\{ f(x(t - 1)) - x(t)\} ,$$ (1.1) where f: ℝ → ℝ is a piecewise continuous function and a ∈ ℝ, a >O. Such equations have found several applications in biology and economics. E.g. they concern the regulation of red blood cell populations [13], [17], excitatory-inhibitory neural interactions [2], [4], [5], regulation of enzyme synthesis [4], respiratory control circuits [12], and modeling of commodity cycles [1].

Serum, liver and renal gamma-glutamyl transpeptidase (GGT) activities were studied in four groups of rabbits: controls, rabbits with obstructive extrahepatic cholestasis, rabbits with obstructive anuria, and animals with combined obstructive extrahepatic cholestasis and obstructive anuria. Serum GGT was essentially increased in rabbits with obstructive extrahepatic cholestasis, showing peak values in the combined cholestasis + obstructive anuria group, and practically normal values in animals with anuria. Liver GGT was increased in both cholestasis groups, but the increase was less prominent than the increase in serum GGT and there was no correlation between them. In both anuric groups renal GGT was reduced, probably as a result of inhibited enzyme synthesis secondary to the altered conditions for adequate renal function. The results obtained are suggestive of a probable renal involvement in the formation of the serum GGT activity level.

For a conclusive description of the action of radiation on single cells, many links between energy absorption and the inability to form a colony are still missing. Studies of physiologic responses of irradiated cells should be helpful in the determination of the events that ultimately may lead to cell death. As part of our investigation of metabolic processes in irradiated yeast cell (see preceding paper), it seemed worthwhile to test if — and possibly how — irradiation interferes with the regulation of enzyme synthesis.

In E, coli ML 39 grown logarithmically histone inhibited, while in the stationary-phase cells histone stimulated the inducible synthesis of β-galactosidase. In the constitative strain ML 308 enzyme synthesis was not influenced. The effect of histone was antagonized by Mg ++ and Ca ++ lons and by spermine.