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On the basis of the analysis of variability of isoenzyme loci and microsatellite loci of nuclear and chloroplast DNA the data were obtained about the degree of differentiation of a number populations of Siberian spruce (Picea obovata Ledeb.), including isolated populations located on the island of Olkhon, in the reserve Bogd-Uul (Mongolia) and on the south of the Magadan region. It was shown that the combined use of various types of genetic markers gives an opportunity to get more complete and objective information about a genetic diversity and intraspecific differentiation of this widespread in Siberia species.

The activity of adenaze in the homogenates of the rabbit's and frog's organs, as well as the ef-fect of Mg++, Cd++ ions on the activity of the enzyme, have been studied. According to the obtained data, Cd++ ions have stronger inhibiting effect on the activity of adenaze. Two isoenzymes have been revealed in each of the studied objects by gel-filtration. It has been demonstrated that the isoenzymes differ in their kinetic properties. [ABSTRACT FROM AUTHOR]

Myocardial infarction in old age is the leading pathology and cause of deaths. The aim of the study was to evaluate the prognostic significance and informative value of cardiac markers of blood in elderly patients with myocardial infarction. The study of cardiac markers in 107 patients with myocardial infarction at the age of 65-75 years and in 83 patients with myocardial infarction at the age of 50-60 years was carried out by immunochromatographic, bioluminescent methods and by electrophoresis on cellulose acetate, followed by the calculation of informativeness and prognostic coefficients. 95 persons aged 65-75 years without myocardial infarction served as control. Troponin T, brain natriuretic peptide, glucose-6-phosphate dehydrogenase and lactate dehydrogenase-1 have the most informative and prognostic significance in elderly patients with myocardial infarction. The use of these cardiac markers will improve the diagnosis and isolation of patients with myocardial infarction at high risk.

The paper addresses genetic causes of stroke: MELAS, antiphospholipid syndrome, CADASIL, Fabry disease. The etiology and pathogenesis, symptoms, diagnosis, treatment methods of these diseases are described.

The study of isoenzymes of leucocyte lactate dehydrogenase (LDH) in healthy men of different age showed a decrease in the membrane-bound pool of LDH-1 and LDH-4 in 40-year-old males as compared with 20-year-old males. The results indicate an age-related reduction of the reserve membrane-bound pool of several LDH isoforms.

The review is dedicated to the signaling pathways triggered by the nitric oxide II in skeletal muscle. Analysis of the current literature shows that during physical exercise of various intensity and regimen the nitric oxide is an essential trigger of the signaling pathways, leading to the alteration of the structural and metabolic myofiber profile and enhancement of its functional capacity. At the same time during the elevated muscle contractile activity (for instance, eccentric activity), NO serves as a protective and stabilizing agent, preventing from the intensification of the proteolytic processes. Data obtained from the experiments with the modulation of the NO at the background of the functional (gravitational) unloading give evidence that neuronal NO synthase activation in this experimental conditions allows to stabilize the degradation pathways and prevent from disuse atrophy development.

The isomeric-structure analysis data of anticholinesterase action of organophosphorous inhibitors with similar structure help in the search of specific effectors and detection of differences in reactivity of various animals' enzymes. This study compared the data of efficacy in respect of 4 mammal and 5 arthropoda cholinesterase preparations for 26 quinolizidine inhibitors, which molecules contain both the isomeric unbranched and branched alkoxyl radicals in the phosphoryl group, and the epimeric lupinine and epilupinine derivatives in the leaving group. The changes in the alkoxyl radical structure of inhibitor molecules act on their efficacy only with respect to the mammal enzymes ("group" inhibitor specificity). The differences between lupinine and epilupinine derivatives were revealed. Highly specific inhibitors of different enzymes were detected among the tested compounds.

A probable mechanism of alteration of the isoenzyme composition of succinate dehydrogenase (SDH) due to differential expression of genes encoding subunit A was considered. The alteration of SDH activity during maize seed germination was investigated, and its maximal activity on day 4-5 of germination was found. The alteration of the sdh1-1 and sdh1-2 gene expression level during maize seed germination was evaluated using the quantitative polymerase chain reaction method. The presence of four forms of the studied enzymes, providing multiple SDH functions was found in maize inflorescence using electrophoresis in polyacrylamide gel.

The polymorphism of beta-phile carboxyesterase (E.C.3.1.1.2) in the males and females of the wild type (Odessa 1) experimental population of Drosophila melanogaster Meigen has been studied with the polyacrylamide disc-electrophoresis. Two isoforms of the enzyme and three phenotypic classes non-uniformly presented among the males and females have been detected. The frequencies of the alleles encoding the corresponding isoforms of the beta-phile carboxyesterase have been determined, as well as those of the genotypes that differed qualitatively and quantitatively with respect to the investigated gene-enzyme system. The deviations of the detected genotype frequencies from the theoretically expected ones were determined. The role of the natural selection directed towards the decreasing of the frequencies of the certain allele is discussed.

A current state of researches on mechanisms of ion homeostasis regulation in the specific conditions of the uncontrolled malignant tumor growth (mainly in carcinomas) concerning the contribution of Na+,K+-ATPase, plasma membrane and sarco(endo)plasmic reticulum Ca2+-ATPases has been reviewed. Particular attention has been focused on the molecular and biochemical links providing the redistribution of the transporting ATPases isozyme pattern for the regulatory requirements of the cell signaling pathways at stable proliferation and viability in malignancy.

In this paper was investigated stability of isoenzymes of lactatdehydrogenase (LDH) of leukocytes of peripheral blood of persons at the age of 20 years (n=10) and more than 65 years (n=8). Extraction of the leukocytes was conducted by centrifugation of human blood on a double gradient of density. Leukocytes were destroyed by hypotonic shock in combination with vibration. Separation of LDH isoenzymes from destroyed leukocytes was conducted by the method of native electrophores. The revealing of activity of LDH isoenzymes was conducted by the method of restoration of nitroblue tetrasolium. Isoenzymes stability was evaluated according to alteration of activity after the incubation of destroyed leukocytes with urea in various concentrations (1M, 2M and 3M). Was shown the presence of three isoenzymes of LDG (LDH-1, LDH-2, LDH-3) in human leukocytes. As the age-dependent alteration of activity of isoenzymes of lactatdehydrogenase in human leukocytes was shown. It can be caused by age-related changes of physico-chemical properties of leukocytes' membranes and/or isoenzymes stability. Stability of LDH-3 was decreased with the age. Observed decrease of LDH-3 stability can be caused by age-related modification of M-subunits of the studied isoenzymes.

Photoinduced changes of structural and functional properties of lactatedehydrogenase isoenzymes from human erythrocytes in free state and in the presence of serotonin have been studied by means of gel chromatography, electrophoresis, IR-spectrophotometry and by the method of definition of catalytic activity. UV-light influence induces photoinactivation of erythrocyte's LDH, while its inhibitory effect intensifies with the increase of irradiation dose. The complicated character of changes in electrophoretic mobility and percentage content of isoenzymes LDH-1, LDH-2, LDH-3 under the influence of UV-rays testifies that the decrease of total enzyme activity of these isoforms in connected with their different photosensitiveness and represents the result of many-staged process which is characterized both by the consistent and parallel proceeding of its individual photochemical reactions. A pronounced photoprotective effect of serotonin towards the molecules of erythrocytic LDH isoenzymes has been discovered. It seems to be caused by formation of enzyme--biogenous amine complex affecting the secondary protein structure.

A new method for encapsulating enzymes by multilayer polyelectrolyte coating is proposed. The method consists in a stepwise adsorption of polyelectrolytes from solution onto protein aggregates formed by salting out the proteins in highly concentrated salt solutions. Polystyrene sulfonate and fluorescence-labeled polyalylamine were used for capsule formation. The size of lactate dehydrogenase aggregates covered by four layer pairs of electrolytes was 1-5 microns, as indicated by fluorescence microscopy. The catalytic characteristics and stability of pig muscle lactate dehydrogenase (EC 1.1.1.13) incapsulated in multilayer electrolyte complex obtained by this method were studied. It was found that the affinity of the substrate pyruvate for the enzyme in the polyelectrolyte complex (K(M)) did not essentially change as compared with the free enzyme. Incapsulated lactate dehydrogenase showed the following features that distinguish it from the free form: (1) the lifetime in diluted solutions increases from 30 min (without capsules) to 1-2 days (in capsules); (2) a higher stability to basic denaturation (up to pH 10); and (3) the absence of substrate inhibition of enzyme in the polyelectrolyte complex. The changes in the catalytic characteristics of incapsulated lactate dehydrogenase are discussed in terms of an increase in effective pK values of amino acid perturbed by polyelectrolyte coating of enzyme.

The content of six lactate dehydrogenase isoenzymes in testes of rats exposed to electromagnetic field of 3-cm wavelength range was studied. The changes in their percent contents were found to be inhomogeneous compared with control. It is assumed that electromagnetic radiation affects the organs of the human urinogenital system. The results can be used for estimating the safety of persons professionally exposed to electromagnetic radiation of the industrial frequency range and in the therapy of diseases of the urinogenital system.

Aim: To specify myocardial affection in adult patients with toxic diphtheria (TD)., Materials and Methods: Along with routine clinical examination 150 patients with toxic diphtheria underwent ECG, echo-CG and biochemical tests. 22, 81, 26, 14 and 7 patients had subtoxic TD, toxic form of the first degree, second degree, third degree and hemorrhagic TD, respectively., Results: Myocardial impairment in TD develops very early, but is diagnosed in different time depending on the diagnostic technique. Early signs of myocardial involvement are activation of cardiospecific enzymes and echo-CG changes. Poor myocardial prognosis in TD is predetermined by progressive cardiac failure (primarily right ventricular), marked conduction disorders, diminished contractility, hyper- or hypoactivity of cardiospecific enzymes., Conclusion: The knowledge of myocardial affection variants in TD enables the clinician not only to predict the disease course but to conduct more adequate therapy resultant in less numerous lethal outcomes of toxic TD.

The paper analyzes the authors' own findings and the data available in the literature on the intensity, site, and possible causes of impairment of the creatine-creatine phosphate system of brain energy metabolism in mental diseases, such as Alzheimer's disease (AD) and schizophrenia. Examining the level of cytosolic BB creatine kinase in postmortem AD and schizophrenic's brain structures showed a significant decrease in BB creatine kinase as compared with the similar control brain structures. There was the maximum decline in AD cases. It was considerable as compared with both the control and schizophrenic groups (p < 0.01). The decrement was revealed by various techniques, including the determination of activity, immunological responsiveness and the analysis of two-dimensional protein maps. Immunocytochemical investigation indicated a decrease in responses to BB creatine kinase, mainly in astrocytes. The reduction in cytosolic BB creatine kinase levels is not a result of age, postmortem delay, or psychotic therapy. The causes of lower BB creatine kinase levels in the cell cytosol of the postmortem brain in mental pathology are discussed. The decrement in cytosolic BB creatine kinase in AD and schizophrenia occurs not only in the brain, but also in the peripheral tissues which contain BB creatine kinase. In all cases, it is greater in AD than in schizophrenia. Using immunosorbents with monoclonal antibodies to M-creatine kinase and to B-creatine kinase subunits makes it possible detect BB-creatine kinase in the extracts of human peripheral lymphocytes and platelets. A study of whether there is a relationship between the clinical data of mental patients and the level of BB creatine kinase in their blood elements is assumed to be useful in evaluating BB creatine kinase as a prognostic/diagnostic marker of mental diseases.

An allozyme variation of loci-encoding lactate dehydrogenase was compared in different vertebrate classes. A lower level of heterozygosity in warm-blooded as compared to cold-blooded vertebrates was shown. The highest heterozygosity was revealed in anurous and caudate amphibians; the lowest, in birds and mammals. Fishes and reptiles exhibited an intermediate level of heterozygosity. In higher groups of vertebrates, differences in the electrophoretic mobilities between alleles decreased. A key aspect of this is a hiatus of these differences in fishes and mammals. On the basis of this analysis, the following conclusions may be drawn: (1) the rate of amino-acid substitutions in homologous proteins is unequal in distant phylogenetic lineages; (2) the level of heterozygosity is related to the average amount of electrophoretic allelic differences at the class level; (3) significant differences in variation pattern in the phylogenetic lineage of vertebrates is probably associated with the evolutionary features of the genomic organization of groups at different evolutionary levels.

Comparative study of the cardioprotective effect of antioxidants emoxipin and hystochrom was conducted in patients with chronic ICD during and after operation for aorto-coronary shunting. Both drugs effectively inhibited LPO activation and reduced the reperfusion damage to the myocardium recorded according to the release of MB-PCK into the blood. The new antioxidant hystochrom proved to be more effective. Its prevalent effect is associated with its higher antioxidant activity.

Comparison of the electrophoretic mobility of various alleles of Ldh-A and B loci within and between species demonstrated a decreased range of variation from fish to anuran amphibians and from anurans to mammals. Fish and mammals feature incompatible ranges of this variation, usually having a mobility range above and below the first zone of Ldh-A and B loci heterodimers, respectively. Amphibians feature both types of variation. Such a quality difference in allelic variation may result from scaling down the amino acid changes from mutation of intragenic regions in fish to single amino acid substitutions in mammals.

An apparent disturbance was revealed in microhaemodynamics of patients diagnosed as having schizophrenia (n = 210) which was more pronounced in continuously progredient form of the above medical condition. An increase in conjunctival indexes, polymorphic character of capillaries, decrease in numbers of capillary loops were revealed by biomicroscopy of the bulbar conjunctiva and capillaroscopy respectively. The patients showed lowering of ATP level and rise in the content of cathodic LDG4-LDG5 fractions, accumulation in blood of lactic and pyruvic acids.

There was investigated that the change of isoenzyme spectrum of laktatdegidrogenaze (LDG) in the dynamic of rats skin wounds healing, and also the activity of some antioxidative enzymes and the accumulation of one lipid peroxidation product (LJO). It was discovered that the enzyme spectrum LDG was reconstructed faster with treated animals by SK preparation. The phase of antioxidative enzymes activity and accumulation of some LFO products were recognized. SQ, the increasing of the katalaza activity in group, where the SK was used.

The study of the melting characteristics of lactate dehydrogenase M4 and Zn/lactate dehydrogenase at pH 6.5-8.5 by microcalorimetric methods shows that in dilute solutions of the enzyme (0.05% lactate dehydrogenase solution) one Zn ion causes destabilisation of enzyme structure, attended by a decrease of melting temperature throughout the entire pH interval under study. Concentrated solutions of the enzyme (0.4% lactate dehydrogenase solution) are a seat of such conformational changes of the latter which affect the character of Zn ions binding depending on pH.

The directed ingression of Lhd-B gene from R. lessonae to R. ridibunda observed during hybridization between these species was confirmed in the present study. The ingression was accompanied by decreased of the initial allele activity, segregative disturbances in heterozygotes and changes in electrophoretic mobility. The population genetic analysis has shown stable preservation of abnormal alleles in hybrid populations. The results are discussed with reference to the concept of genetic instability, its application to speciation models, and the neutralist vs. adaptationist controversy. Our data supports the neutral concept of allozyme variation.

Lactate dehydrogenase-C4 (LDH) is a specific cell isoenzyme of spermatogenesis and spermatozoa of man and animals. Due to the lower levels of contaminating proteins, isolation of LDH C4 from spermatozoa had a lot of advantages. LDH C4 was isolated as follows: precipitation with ammonium sulfate, separation of LDH C4 from other LDH isoenzymes using immunosorbents, purification from contaminating proteins of oxamate-Sepharose. Antibodies to LDH1-3 immobilized on tresyl-Sepharose were used as immunosorbents. Elution of LDH C4 from oxamate-Sepharose by means of lithium lactate appeared inadequate therefore LDH C4 was eluted using 0.63 mM sodium pyruvate.

Factors affecting activity and isoenzyme pattern of creatinine kinase in animal tissues, were analysed. Based on the analysis and study of creatine kinase systems at the molecular, cellular, tissue and organism levels, the activity and isoenzyme pattern of creatinine kinase was shown to be able to serve as an indicator of the organism functional state.

The lactate dehydrogenase (LDH) isoenzyme profile was studied in bioptic samples of gastric mucosa taken from 57 infantile patients suffering from chronic gastroduodenal pathology and 7 children with gastric functional disorders. The investigation showed LDH1 level to decrease and that of LDH5 to increase, the LDH5/LDH1 ratio increasing accordingly, in cases of erosive gastro-like gastroduodenitis and duodenal ulcers. The degree of said changes was found to correlate with the extent of morphological lesions of gastric mucosa and the most pronounced changes were recorded in cases of gastric mucosa gland atrophy. Similar changes in LDH isoenzyme profile had been identified in patients with gastric tumors. Said findings may be used in identification of groups at high risk for gastric carcinoma.

Changes of lactate-dehydrogenase (KF 1.1.1.27) activity have been studied in the liver of the bream been infected with pleurocercoids of the cestode Digramma interrupta. It is showed, that an increase of enzyme activity depends upon a slowly migrating from LDH-6. Problems of interaction at the level of substrate within a system parasite-host is considered.

The possibility of using isozyme and PCR markers for estimation of preservation of human chromosomes in human.rodent somatic cell hybrids is considered. Methods of electrophoretic separation of 33 isozymes and 11 PCR markers for 22 human autosomes and X chromosome are described. Using these isozymes and PCR primers as markers of known regions and arms of human chromosomes, one can avoid errors in typization of chromosomes with complicated rearrangements which simulate similar patterns of G-banding. The method proposed in the paper not only facilitates considerably the analysis of hybrid clones, but is also an easy and reliable tool in selection of somatic cell hybrid clones for further investigation.

The content of brain isoenzyme of creatine kinase (CPK BB) was studied in cytosolic fraction of brain extracts of normal and mental patients. The CPK BB content was determined using immunoblotting technique in 10 different brain structures, including some cortex areas, hippocampus, cerebellum cortex, n. caudatus, putamen and inferior oliva. The present work demonstrates a severe decline of CPK BB concentration in all mental brain structures studied, especially in occipital cortex, hippocampus and oliva. The decrease of CPK BB level was more pronounced in Alzheimer's disease patients.

Two methods--electrocardiographic (recording ECG cartograms in 35 leads) and biochemical--for assessing myocardial necrotic formation in the convalescents and death victims of myocardial infarction, were compared. The author considered changes in the number of complexes with ST segment elevation and Q wave square (QS) out of ECG parameters. There were uniform changes both in electrocardiographic parameters, and in the peripheral blood activity of creatine phosphokinase MB, an isoenzyme specific to the myocardium. There were significant differences between the changes in the death victim group as compared to the convalescents. It is shown that myocardial infarction is a process which is extended in space and time rather than momentary.

Physiological parameters, rates of mitochondrial respiration, high energy phosphate levels and creatine phosphokinase (CPK) activity were investigated in the hearts from control and alloxan-induced diabetic rabbits before and after 40-min total ischemia and reperfusion. Diabetic hearts demonstrated significant decreases in the rates of contraction (+dP/dt) and relaxation (-dP/dt), heart rates and cardiac work compared to control hearts. Determination of mitochondrial respiration rates in saponin-skinned fibers showed a low mitochondrial respiratory function in diabetic hearts. It was found that the ATP and ADP levels and the total and mitochondrial isoenzyme activities of CPK in diabetic hearts were lowered in comparison with control. A post-ischemic recovery of cardiac performance for diabetic hearts was better than in controls. After reperfusion diabetic hearts had increased ATP levels. The data obtained demonstrate some abnormalities of both cardiac performance and energy metabolism in the hearts of diabetic animals and a decreased sensitivity of the latter to ischemic injury.

The structure-function peculiarities of human, porcine, rabbit, and rat lactate dehydrogenase (LDH) isoenzymes have been studied using antipeptide antibodies (AB) against the M4-isoform of porcine LDH. Antipeptide AB were raised against the hypervariable (40% homology) N-terminal fragment (residues 1-32), and the highly conservative fragment 180-214 containing histidine in the enzyme active center. Whereas antipeptide AB against the fragment of the active center of porcine LDH M4-isoform selectively inhibited the catalytic activities of LDH isoenzymes from various sources, antipeptide AB directed against the N-end were without effect. The ability of antipeptide AB to specifically interact with various isoforms of LDH suggests that sequences 1-32 and 180-214 are immunochemically identical only in the case of human and porcine M4 isoenzymes; the relatedness of the amino acid sequence to the common antigenic determinant required the absence in the given sequence of essential amino acid substituents. Chemical modification of porcine M4-isoform by diethylpyrocarbonate and the use of specific AB revealed that histidine-195 located in the active center of LDH is not directly involved in the binding to AB.

Reversible short-term and local myocardial ischemia in non-anaesthetized dogs involved a functional (if changing the activity of CPK) and morphologic aftereffect. At the same time it is possible to find some mechanisms of compensation (in chronic experiment).

Kinetic parameters of rat creatine kinase isozymes at different vitamin K supply and treatment with antivitamin K--pelentan have been determined. MM-isozyme (skeletal muscle) has selective sensitivity to the vitamin K deficit, while BB and MB-isozymes (brain, kidney and heart) have not. The value KM for ATP of MM-isozymes increases, while maximal activity decreases. Pelentan treatment does not lead to the change of MM-creatine kinase affinity to ATP. Soluble hexokinase of skeletal muscle in rats with vitamin K deficiency and treated with pelentan has higher affinity to glucose as compared to normal rat enzyme. It has been supposed that skeletal muscle hexokinase exists in a particular molecular form under vitamin K deficiency.

It has been shown that there is a decrease in the content and activity of three neurospecific proteins (neurospecific enolase--NSE, glial fibrillar acid protein--GFAP and creatine kinase CK BB) in various structures of the postmortal brain of schizophrenic patients and those with senile dementia and Alzheimer's disease. The differences in the intensity and localization of these disorders in the above patients' groups have been detected. A previously unknown component of a pathological process in the brain, indicated by the decrease of the CK content and activity has been discovered. It is suggested that the decrease of the content of CK BB results in the development of energy deficit in the brain in patients with mental disorders.

As far as the pathogenesis of poisonings with organophosphorus pesticides is concerned, in addition to irreversible inhibition of acetylcholinesterase (AGE) in tissues, of importance are changes in the other systems which essentially determine the outcome of intoxication. The purpose of the present study was to examine the nature of changes occurring in total protein and protein fractions, free amino acids (aspartic and glutamic acids, glycine, isoleucine, leucine) and in certain enzymes (AST, ALT, CP, GGTP, GDH) in the cerebrospinal fluid (CSF) of patients with acute Malathion insecticide poisoning. 137 patients aged 20 to 50 years were placed under observation. There were 77 men and 60 women. 40 persons had poisoning of medium gravity and 97 were severely poisoned. The intake of the CSF was performed on days 1, 3, 10, 14 and 21 since the disease onset. It has been established that in acute Malathion insecticide poisoning, the CSF content of the stimulating mediator amino acids, aspartic and glutamic, rises within the early periods, whereas the concentration of the inhibitory mediator glycine decreases. The changes in protein fractions of the CSF are characterized by a fall of the content of globulins and a rise of albumins, thus attesting to the predominance of pathological processes in the brain, especially in the initial period of intoxication, and to the impairment of the blood-brain barrier. The development of intoxication is associated with activation in the CSF of LDN, CP, GGTP and GDH as well as by activation of LDH isozymes which is viewed as the result of the membranotoxic effect of a Malathion insecticide.

The present study describes a few morphological and neurochemical disturbances in astroglial cells in senile dementia of the Alzheimer type (SDAT). The greatly elevated number of fibrous astrocytes in brain samples with SDAT is observed. The content of glial fibrillar acid protein is elevated in these cells. Glial filaments are detected to surround lipid centers. Moreover, there are deviations in energy metabolism: a profound decrease in the levels of the brain creatine kinase CKBB that is one of the principle ATP-regulation enzyme. It is suggested that there is a relationship between all the disturbances observed in glial cells of SDAT patients. These disturbances are likely to be links of the same process which leads to abnormal brain ageing.

Regulating effect of individual phospholipids on the activity of creatine kinase MM from human myocardium was studied. Cardiolipin, phosphatidic acid, phosphatidyl serine and phosphatidyl choline (dipalmitoyl) stimulated the enzymatic activity, while phosphatidyl inositol and lysophosphatidyl choline inhibited the creatine kinase MM activity by 80-100%. When mechanisms of the phospholipids inhibitory effects were studied, mixed type of inhibition was detected in the presence of phosphatidyl inositol and non-competitive type--in presence of lysophosphatidyl choline if guanidine was used as a substrate. Phosphatidyl inositol and lysophosphatidyl choline inhibited creatine kinase MM by the uncompetitive type if ADP was used as a substrate.

Antigenic properties of human, pig, rabbit and rat lactate dehydrogenase (LDH) M4-isozyme as well as of human LDH-C4 were studied using antipeptide antibodies against pig LDH-M4 fragment (180-214). Amino acid sequence 180-214, containing His-195, which is involved in the active site of LDH isozymes, proved to be total antigenic determinant only for human and pig M4-isozymes. Amino acid sequence of total antigenic determinant did not allow any substitutions of essential amino acid residues. His-195, participating in substrate binding, was not involved immediately in reactions with antibodies as shown by means of chemical modification of pig M4-isozyme with diethyl pyrocarbonate and after production of antibodies against the modified isoenzyme.