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This article is the sixth and last of a series devoted to the primary structure of bovine β-casein [1–5]. In the preceding paper, we presented a partial sequence of this protein in which 156 out of the 209 amino-acid residues were exactly positioned [5]. Only a few data were given on the tryptic peptides T2 and T3 [1] which corresponded to the unknown part of the molecule. In the present communication, we establish the amino-acid sequence of these 2 peptides, and discuss the salient features of the β-casein molecule. Bovine β-casein A2 is a phosphoprotein constituted of a single polypeptide chain containing 209 amino-acid residues. Among them are five phosphoseryl residues. From sequence data, it can be written: Asp4, Asn5, Thr9, Ser11, SerP5, Glu17, Gln22, Pro35, Gly5, Ala5, Val19, Met6, Ile10, Leu22, Tyr4, Phe9, Trp, Lys11, His5, Arg4. Its exact molecular weight is 23982, a little higher than that of αs1-casein, which is 23616 [6]. The total number of 27 amide groups (Asn + Gln) agrees well with previous data obtained by Pion et al. [7] and Peterson et al. [8]. The average hydrophobicity, calculated according to Bigelow [9], is 1330 and it places β-casein among the most hydrophobic proteins. The sequence obtained emphasizes the uneven charge distribution along the peptide chain. A high negative net charge is located in the first 50 residues. The high proline residue content (16.7%) and the rather uniform repartition of this residue exclude the possibility of a high α-helix content. Furthermore, the complete absence of segments containing more than 2 adjacent prolyl residues seems to preclude the possibility of poly-L-proline structure that was expected from optical-rotatory-dispersion studies [10]. An interesting extension of the present work is the discovery by Gordon et al [11] that γ-, TS-, R- and S-caseins are fragments of β-casein likely originating from tryptic-like cleavages of the peptide chain next to the carbonyl groups of some lysyl residues. The γ-, TS. A2- and S-, TS. B- and R-caseins respectively represent residues 29 to 209, 106 to 209 and 108 to 209. These results explain the occurrence of only one phosphorus atom in the γ-caseins, the absence of phosphorus in the TS-, R- and S-caseins [12]. Localization of the substitutions which differentiate the known variants of bovine β-casein also explains the relationship between β-, γ-, R-, S- and TS-caseins [12,13]. The NH2-terminal tryptic phosphopeptide, previously analyzed by Peterson et al. [14], has been sequenced independently by Manson and Annan [15]. Their results are identical to those reported in a preceding paper [4]. [ABSTRACT FROM AUTHOR]

Previous reports [1-5], we have described some of the features of the primary structure of bovine αs1-casein. In the present work, the complete amino acid sequence has been established and the salient features of this phosphoprotein have been discussed. In the polyeptide chain, the region containing the phosphopeptides Tm1 (T1-T2), Tm1T2 and Tm1T1 [1,4,5], had only been slightly studied as yet. Because of the difficulties encountered in the breakdown of these phosphopeptides, hydrolysis with endopeptidases and exopeptidases were performed on both native and dephosphorylated peptides. It was confirmed that peptide Tm1T2 contains three hydroxy-amino acids (2 Ser, 1 Thr), but, instead of three [1], two phosphorus atoms were found with purified preparations. Partial acid hydrolysis and dephosphorylation using an orthophosphoric-monoester phosphohydrolase indicate that the two seryl residues m this peptide are O-phosphorylated. The remaining gap in the sequence of the central part of peptide Tm1T2 was bridged by studying two fragments obtained by papain digestion of the dephosphorylated preparation. Instead of four serines, postulated earlier from the results of the amino-acid composition of peptide Tm1T1 [1], five were shown to be present after detailed analysis of the fragments. Since the five phosphate groups could be ready removed by an orthophosphoric-monoester phosphohydrolase, the five seryl residues could be O-phosphorylated. The fragments obtained after hydrolysis with thermolysin of both native and dephosphorylated peptide Tra1T1 were further degraded using classical methods for the determination of the amino acid sequence. In the light of all the results obtained on this phosphoprotein (αs1-casein B), the total number of amino acid residues has been corrected to 199, instead of 198, as reported previously [1-5], and the molecular weight has been calculated to be 23616. The following amino-acid composition; Asp7, Asn8, Thr5, Ser8, SerP8, Glu25, Gln14, Pro17, Gly9, Ala9, Val11, Met5, Ile11, Leu17, Tyr10, Phe8, Lys14, His5, Trp2, Arg6, indicates that there is a higher number of acidic than basic residues in this protein. On the basis of the intrinsic dissociation constants of titratable groups in proteins [6], the negative net charge of the molecule was estimated to be 22 at pH 6.5 and 28 at pH 8.6. Since Bigelow's parameter for thc average hydrophobicity [7] of this protein is 1170, it could be considered to be a hydrophobic protein The high amount (8.5%) and uniform distribution of prolyl residues indicate that this protein has limited structuralcoiling possibilities. The polypeptide chain contains three hydrophobic regions, viz. 1-44, 90-113 and 132-199. The first two are characterized by the fact that basic residues predominate over acidic residues. The third region, where most of the aromatic residues are located, contains very few basic residues and is therefore of more acidic character. Two regions, 45-89 and 114-131, are hydrophilic. The former contains more than half of the total acidic residues, in particular seven of the total eight phosphoseryl residues. Another remarkable feature is the concentration of amino acids with carboxylic side chains, particularly glutamic acid, in the vicinity of two clusters of phosphoseryl residues. It may be noticed that the phosphoseryl residues m αs1-casein are arranged m a manner similar to those in β-casein [8]. In particular, in αs1-casein, the 62-70 region containing four phosphoseryl residues, is similar to the 13-21 region in β-casein [8]. It is interesting to point out that ail but one of the phosphoseryl residues always occur m position n with relation to a glutamyl or a phosphoseryl residue, which is in position n + 2. From this, it would appear that there is an enzymatic phosphorylation of the polypeptide chum (carried out by a phosphoryl kinase which may require a negative charge in the phosphorylation site) rather than a direct incorporation of phosphoserine into the polypeptide chain during protein synthesis. The location of the amino-acid substitutions that characterize the αs1-Casein D and the β-casein C variants has provided evidence for an enzymatic phosphorylation of casein [9]. The problem of the phosphorylated sites in αs1- and β-caseins will be discussed in a forthcoming paper. The repeating amino-acid sequences located in the two regions of αs1-casein, viz. 70-84 and 110-125, are also of interest. The primary structure of αs1-casein given here is that of the genetic variant B. The three other variants A, C and D have also been studied. The C and D variants differ from the B variant by the substitutions of Gly/Glu in position 192 [10] and ThrP/Ala in position 53 [9], respectively. The A variant is characterized by a deletion of thirteen amino-acid residues from position 14 to position 26 in the hydrophobic NH2-terminal part of the polypeptide chain [11]. Because of this deletion, there m an important change in the physico-chemical properties of αs1-casein [12, 13]. Some important features of the amino-acid-sequence determination should be noted. Firstly, the great value of maleic anhydride as a reversible-blocking reagent for amino groups of proteins [14], and the usefulness of thermolysin as a specific enzyme for degrading polypeptides [15]. Secondly, the difficulties encountered during the study of the phosphopeptides: these peptides were difficult to purify since they have similar anionic characters and only react slightly with ninhydrin during paper revelation; other difficulties have been the high destruction of phosphoserine during hydrolysis with HCl 5.7 N, the poor yield in the substractive Edman degradation when the NH2-terminal residue is a phosphoserine, and the failure of endopeptidases and exopeptidases to split off peptide bonds that are close to phosphate groups. Fortunately, alkaline phosphatase has proved to be a useful tool for removing phosphate groups, thus avoiding most of these difficulties. Since the amino-acid sequence of αs1-casein is now known, the degradation of this protein by coagulating and other proteolytic enzymes during cheese ripening may be studied. In particular, bitter peptides originating from αs1-casein may be located. As we have already briefly noted [4], it is obvious that one of the three bitter peptides isolated by Matoba et al. [16] from a tryptic hydrolysate of whole casein, was the segment 23-34 of the polypeptide chain of αs1-casein. In addition, the knowledge of the primary structure will be of help in understanding many aspects of the relations between structure and physical properties in this phosphoprotein. [ABSTRACT FROM AUTHOR]

The article presents information on a research paper regarding the basic facts and principles of radioactivity and properties of radioisotopes related to this. This paper is a back-ground work for the more specialized treatments and applications appearing in this regard. The present state of atomic science is the culmination of researches resulted in three monumental discoveries such as X-rays, radioactivity and the electron that provided novel and powerful methods for studying the nature and the structure of the atom. Later investigations revealed that radioactivity is a property of the atom and thus it is a nuclear phenomenon. The nature of these radiations was resolved into three types of rays, the alpha, the beta and the gamma rays. Further studies revealed that the elements that have radio activity die away according to an exponential law. Scientists adopted some convenient definition of the life of a radio active element that is usually called the half-life period. Based on this they defined the properties of radioisotopes as well.

The article discusses safety measures in the handling of radioactive materials. The biological effect of radiation is the combined result of the production of ion pairs in tissue and the excitation of atoms or molecules by radiation which does not have sufficient energy to cause ionization. The problem of tolerance dose is chiefly concerned with the radiosensitivity of the tissues. The three categories of radiochemical operations are low levels, intermediate levels and high levels. Requirements in the construction of radioisotopes laboratory, including floors, surfaces, tables, sinks and hoods are discussed. Safe practices to reduce contamination are also described.

[1-²H2]Ethanol, [2-²H3]ethanol and [1-13C, 1-²H2]ethanol were administered to bile fistula rats under conditions ensuring a maximal rate of oxidation for about 24 h. Cholesterol, cholic acid, chenodeoxycholic acid and 3β,11β,21-trihydroxy-5α-pregnan-20-one were isolated from bile collected at intervals during the experiment. The fraction of molecules containing different numbers of heavy isotope atoms was measured by gas chromatography-mass spectrometry-computer techniques. The results were used to determine the origin of the cholesterol pools used as precursors for the different compounds isolated from bile. The bile acids were found to be formed from a cholesterol pool, the turnover of which was about 5 times more rapid than that of the cholesterol pool used for biliary excretion. The cholesterol pools used for biliary excretion and as corticosterone precursor seemed to be in equilibrium. The acetyl groups derived from ethanol were introduced into the steroids without exchange of hydrogens at C-2, and the acetyl-CoA pool used as precursor did not exchange with acetyl groups in e.g. citrate or fatty acids. A difference in incorporation of [2-²H3]acetyl groups and [1-13C]acetyl groups was interpreted to be due to an isotope effect. Ethanol contributed about 45% of the acetvl-CoA pool used as precursor of cholesterol and bile acids. Deuterium from [1-²H2]ethanol was incorporated in many positions of all the steroids. If it is assumed that the incorporation is mediated by NADPH, the deuterium excess of the hydrogens introduced was about 10 atoms %. The contribution via different pathways of an important part of the hydrogen and carbon atoms in cholesterol, bile acids and corticosteroids provides possible mechanisms by which ethanol may affect the biosynthesis and metabolism of steroids. [ABSTRACT FROM AUTHOR]

The corrinoids are a group of compounds containing four reduced pyrrole rings joined into a macrocyclic ring by links between their a positions; three of these links are formed by a one-carbon unit, methylidyne radicals and the other by a direct Ca-Ca bond. They include various B-12 vitamins, factors and derivatives based upon the skeleton of corrin. The atoms are numbered and the rings are lettered. The numbering is thus the same as that of the porphyrin nucleus, number 20 being omitted to preserve the identity.

The ability of the yeast Cryptococcus terricolus to oxidize various, saturated, normal fatty acids containing between two and eighteen carbon atoms, the unsaturated acid oleic acid, and two terminally branched fatty acids, was studied. The organism was found to be capable of oxidizing all the acids tested. Great variations in the oxidation rates and in the extent of oxidation of the different acids were found. These variations were dependent on the chain lengths of the fatty acids, the oxidation activity increasing as the chain lengths decreased from eighteen to ten carbon atoms. In addition to the presence of a permeability barrier, a toxic effect, which was most pronounced at alkaline pH values, was found. Addition of ammoninm ions to cells oxidizing fatty acids resulted in an increased oxygen uptake. The oxidation rates of different fatty acids were greatly increased by adding 2,4-dinitrophenol (10-4 M) to the cells. The resulting, total oxygen uptake was, in most cases, far beyond the theoretical maximum calculated on the basis of complete oxidation of the added fatty acids to carbon dioxide and water. However, the rate and the extent of the oxygen uptake, due to the endogenous oxidation, were also greatly increased by adding 2,4-dinitrophenol. The increased oxidation of the endogenous reserves remained on a high level after the addition of extracellular substrates, explaining the apparent supra-maximum extent of oxidation. A greatly increased endogenous oxidation was also found when fatty acids, containing between four and nine carbon atoms, were used as substrates. The principal difference between the mode of action of 2,4-dinitrophenol and that of fatty acids with intermediate chain lengths on the endogenous oxidation, is discussed. [ABSTRACT FROM AUTHOR]

Determinations of the molcular weight by aid of gel filtration demonstrate that ferredoxin from Clostridium pasteurianum can exist as well in a monomeric (Mr = 6000) as in a dimeric form (Mr= 12000). The dimerisation takes place in the presence of oxygen. Using exactly anaerobic conditions pure monomeric material can be prepared; using aerobic conditions, however, pure dimeric material or a mixture of monomers, dimers, and apoferredoxins of higher molecular weights appear. Comparing the analytical data of the active center one finds eight atoms of iron and labile sulfur in monomeric ferredoxin, whereas four atoms of iron and labile sulfur are found in the subunit of dimeric ferredoxin. Results of the determination of the Hg-content in mersalyl-apoferredoxin prepared from a dimeric sample and of the titration of free SH-groups in monomers and dimers can be explained assuming that four cysteinyl residues per subunit participate in disulfide bridges in dimeric ferredoxin. That means, dimerisation is accompanied by a loss of iron and labile sulfur and therefore by a decrease of the absorption coefficient ε390 = 30000 M-l × cm-1 to ε390 = 15000 M-1 × cm-1 related to one subunit with the molecular weight of 6000. The ratio of absorbances A390: A280 seems to remain unchanged. In the phosphoroclastic system the biological activity of the dimeric ferredoxin decreases by a factor of two referring to one subunit. [ABSTRACT FROM AUTHOR]

Deuterium-hydrogen exchange has been used to detect possible conformational changes accompanying the interaction of ribonuclease A with two competitive inhibitors cytidine 3'- phosphate (Cyd-3'-P) and cytidine 2'-phosphate (Cyd-2'-P). An improvement of the cryosublimation technique was employed and combined. with mass spectrometry measurements of sample deuterium content. Exchange kinetics were followed from 1 min to 24 h, at pH 6.5, and 38&degree;C (0.1 M NaCl). Two methods were used to present the data: a graphical exponential-curve-fitting and a numerical analysis. They both lead to the same conclusions. Four different classes of hydrogens were found. Among them, the one involving the instantaneously exchanged atoms is increased by about ten hydrogens after the binding of these inhibitors, the number of unexchanged hydrogens (within 24 b) is hardly altered in the presence of Cyd-3'-P whereas it is decreased by one third after the fixation of Cyd-2'-F. These exchange results suggest that both inhibitors induce in ribonuclease A conformational changes which may be correlated with inhibitor strength. [ABSTRACT FROM AUTHOR]

Discusses the abbreviations and symbols for the description of polypeptide conformation. Designation of atoms; Bond lengths; Sequence rule; Choice of torsion angle; Polarity of hydrogen bonds; Symbols for atoms and bonds in the side chains of the commonly occurring L-amino acids; Symmetry and hydrogen-bond arrangements.

Using the classical hapten inhibition technique, antibody binding sites on the chloramphenicol molecule were explored. Sixteen compounds related to chloramphenicol, but with varying degrees of change in theft structurce were examined for inhibiting ability at 1-, 10- and 100-&mug levels. The removal of the two chlorine atoms accounted for the greatest loss of antibody binding capacity. The major antigenic sites are separate from the sites critical for the antibiotic activity of chloramphenicol. [ABSTRACT FROM AUTHOR]

The article focuses on an X-ray tube developed by the scientists of the Department of Terrestrial Magnetism of Carnegie Institution. The scientists succeeded in creating a higher electrical voltage than what has ever been produced, using relatively inexpensive apparatus at the laboratories in Washington. The high electrical voltage aids in the study of the structure of matter. The high voltages might also be used to produce radiations on a small scale. It has been proved by scientific investigation that different kinds of atoms combine to form molecules which combine to form objects. The mass of the atom is concentrated in the nucleus. A very intense X-radiation would be produced by a high-voltage tube since the efficiency of X-ray production becomes greater with rise in voltage. Such tubes could be used to take X-ray pictures. The X-rays could also be used to find out flaws in thick castings. The effects of radiations on biology cannot be predicted.