Recognition of aminoethylhomocysteine and aminopropylcysteine by aminoacid transport systems and aminoacyl tRNA synthetases

In E. coli aminoethylhomocysteine (AEHC) and aminopropylcysteine (APC) do not affect intracellular lysine transport thus showing that they cannot bind the E. coli lysine transport systems. In CHO cells AEHC and APC inhibit lysine and arginine transport, AEHC more than APC, thus indicating that they can bind the cationic aminoacid transport system. They inhibit also leucine transport, APC more than AEHC. Some possible relationships between their structure and their effects on transport systems are considered. AEHC and APC are not activated by aminoacyl-tRNA synthetase preparations from bacterial and mammalian sources.

Chemical modification of histidine, tyrosine, tryptophan and cysteine residues in carp (Cyprinus carpio) muscle enolase

Enolase from carp (Cyprinus Carpio) muscle was modified by diethylpyrocarbonate, tetranitromethane, N-bromosuccinimide and 5,5'-dithiobis(2-nitrobenzoic acid). The extent and rate of modification and its effect on the enzyme activity were determined. Modification of histidine, tyrosine and tryptophan residues caused complete inactivation of the enzyme; Mg2+ as well as 2-phosphoglycerate markedly altered the rates of modification and inactivation. The above-mentioned amino acid residues seem to be essential for the functioning of muscle enolases. Modification of cysteine residues had no effect on the enolase activity.

Disulphide bonds are a requirement for adsorption of cephalosporins on the red cell membrane

The authors studied the behavior of red cells (RBCs), treated with 2-aminoethylisothiouronium bromide (AET), against 100 serums containing cephalothin antibodies and 27 serums with cephapirin antibodies. None of the serums reacted with cephalosporin-coated RBCs that had been exposed previously to AET. The possibility of the Kell system acting as a receptor for cephalosporins was excluded. The authors discuss the significance of cysteine disulphide bonds and the tertiary or quaternary structure of red cell membrane proteins in the binding of cephalosporins to RBCs.

Formation and reduction of glutathione-protein mixed disulfides during oxidative stress. A study with isolated hepatocytes and menadione (2-methyl-1,4-naphthoquinone)

Incubation of isolated rat hepatocytes with menadione (2-methyl-1,4-naphthoquinone) resulted in a dose-dependent depletion of intracellular reduced glutathione (GSH), most of which was oxidized to glutathione disulfide (GSSG). Menadione metabolism was also associated with a dose- and time-dependent inhibition of glutathione reductase, impairing the regeneration of GSH from GSSG produced during menadione-induced oxidative stress. Inhibition of glutathione reductase by pretreatment of hepatocytes with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) greatly potentiated both GSH depletion and GSSG formation during the metabolism of low concentrations of menadione. Concomitant with GSH oxidation, mixed disulfides between glutathione and protein thiols were formed. The amount of mixed disulfides produced and the kinetics of their formation were dependent on both the intracellular GSH/GSSG ratio and the activity of glutathione reductase. The mixed disulfides were mainly recovered in the cytosolic fraction and, to a lesser extent, in the microsomal and mitochondrial fractions. The removal of glutathione from protein mixed disulfides formed in hepatocytes exposed to oxidative stress was dependent on GSH and/or cysteine and appeared to occur predominantly via a thiol-disulfide exchange mechanism. However, incubation of the microsomal fraction from menadione-treated hepatocytes with purified glutathione reductase in the presence of NADPH also resulted in the reduction of a significant portion of the glutathione-protein mixed disulfides present in this fraction. Our results suggest that the formation of glutathione-protein mixed disulfides occurs as a result of increased GSSG formation and inhibition of glutathione reductase activity during menadione metabolism in hepatocytes.

Antiviral and antiproliferative activities of interferon-alpha 1: the role of cysteine residues

Site-specific in vitro mutagenesis was used to direct serine for cysteine substitutions within the sequence of human interferon-alpha 1 (IFN-alpha 1). Antiviral specific activities and antiproliferative activities of IFN-alpha 1 analogs, expressed in M13 as fusion proteins, were assessed following purification by monoclonal antibody affinity chromatography. Based on analysis of IFN-alpha 2, IFN-alpha 1 contains two disulfide bridges between cysteine residues 29 and 139 and cysteine residues 1 and 99. IFN-alpha 1 also contains a fifth cysteine residue at position 86. The series of serine for cysteine substitutions performed indicated that IFN-alpha 1 molecules unable to form the residue 29 to residue 139 disulfide bridge have substantially reduced antiviral and antiproliferative activities, IFN-alpha 1 molecules unable to form the residue 1 to residue 99 disulfide bridge have only marginally altered antiviral and antiproliferative activities, the low antiviral activity of IFN-alpha 1 compared with other human IFN-alpha subtypes is not due to the formation of nonnative disulfide bridges involving the fifth cysteine residue at position 86, which the other subtypes lack, and (iv) the reduced biological activities of certain analogs may be due to the formation of nonnative disulfide bridges.

Disulfide bonds and the translocation of proteins across membranes

We are concerned with the mechanisms whereby hydrophilic proteins synthesized in the cytoplasm are translocated across one or two membranes into different cellular organelles. On the basis of a model of the translocation process to be described elsewhere, we propose an explanation of previous findings that the in vitro translocation across the endoplasmic reticulum of secretory proteins of higher eukaryotic cells appears to be obligatorily co-translational (i.e., occurs only while the polypeptide chain is being synthesized on the ribosome). We suggest that in vitro the intrachain disulfide bonds of the polypeptide rapidly form after it is released from the ribosome; the three-dimensional conformation of the chain is thereby stabilized and cannot undergo the unfolding that is required for post-translational translocation. In accord with this proposal, we show that the secretory preprotein human preprolactin, after translation and release from the ribosome, can indeed undergo translocation across endoplasmic reticulum membranes in vitro if the medium is sufficiently reducing. Those polypeptides that, in the absence of reducing agents, can be post-translationally translocated in vitro across bacterial, mitochondrial, and other types of membranes may generally lack intrachain disulfide bonds.

Sulfate transport-deficient mutants of Chinese hamster ovary cells. Sulfation of glycosaminoglycans dependent on cysteine

We isolated 59 Chinese hamster ovary cell mutants defective in 35SO4 incorporation into glycosaminoglycans. Thirty-five mutants incorporated [6-3H]glucosamine into glycosaminoglycans normally, suggesting that they were specifically impaired in sulfate incorporation. Cell hybridization studies revealed that the 35 mutants defined a unique complementation group. Pulse-labeling one of the mutants with 35SO4 showed that it possessed a defect in a saturable, 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonic acid-sensitive transport system required for sulfate uptake. Despite the dramatic reduction in 35SO4 incorporation, the mutant synthesized sulfated heparan and chondroitin chains. Incubation of the mutant with [35S]cysteine resulted in the formation of 35SO4, which was subsequently incorporated into the glycosaminoglycans. Similar results were obtained when wild-type cells were incubated in sulfate-free growth medium containing [35S]cysteine, and isotope dilution analysis indicated that about 15 microM of sulfate was derived from cysteine catabolism. We also found that the sulfate transport deficiency rendered the mutant resistant to 5 microM sodium chromate, whereas wild-type cells did not divide under these conditions. However, the mutant also did not proliferate in medium containing 5 microM chromate when grown in the presence of wild-type cells, suggesting that chromate was transported through cell-cell contacts. Since co-cultivating sulfate transport-deficient mutants with mutants defective in xylosyltransferase or galactosyltransferase I partially restored 35SO4 incorporation into glycosaminoglycans, intercellular sulfate transport occurred as well. Therefore, the availability of sulfate for glycosaminoglycan synthesis depends on sulfate uptake, turnover of sulfur-containing amino acids, and sulfate transport between cells.

Chemical modification of alpha 2-adrenoceptors. Possible role for tyrosine in the ligand binding site

Tetranitromethane (TNM) is a reagent which reacts with the tyrosine and cysteine residues of proteins. Chemical modification of partially purified human platelet alpha 2-adrenoceptors with TNM resulted in an irreversible loss of binding activity. Typically, an 80-90% decrease in binding activity occurred with a 60-min exposure to 320 microM TNM. The loss of alpha 2-adrenoceptor activity caused by TNM could be prevented if alpha 2-adrenergic ligands were present during exposure of the receptor to TNM. The protection afforded by alpha 2-adrenergic ligands was dose-dependent and showed a positive correlation with the affinity of the ligand for the alpha 2-adrenoceptor. Prazosin, an alpha 1-specific antagonist, and propranolol, a beta-adrenergic antagonist, did not protect alpha 2-adrenoceptors against the inactivation caused by TNM. Saturation curve analysis revealed that the decrease in alpha 2-adrenoceptor activity caused by TNM was due to a decrease in Bmax with no change in Kd. alpha 2-Adrenoceptors were also inactivated with the sulfhydryl-specific reagent phenylmercuric chloride (PMC). The receptor inactivation caused by PMC could be reversed completely by subsequent treatment with dithiothreitol. Treatment of alpha 2-adrenoceptors with combinations of TNM and PMC showed that the receptor inactivation caused by TNM was most likely due to an interaction with tyrosine residues. These results indicate that tyrosine residues have a function in the conformational stability of alpha 2-adrenoceptors and may be directly involved with ligand binding to the receptor.

Potassium activation and its relationship to a highly reactive cysteine residue in fructose 1,6-bisphosphatase

The specific chemical modification by sodium cyanate of highly reactive cysteine residues at pH 7.5 in pig kidney fructose 1,6-bisphosphatase results in the reversible loss of activation of the enzyme by monovalent cations. No loss of activation by potassium ions occurs when modification is carried out in the presence of fructose 2,6-bisphosphate. The effect of Mg2+ on native and cyanate-modified enzyme activities implicates the above cysteine residue as being directly linked to the inhibition by both the divalent cation and fructose 2,6-bisphosphate. Incorporation of [14C]cyanate to the enzyme shows that the blockage of two reactive residues per tetramer is sufficient to eliminate the activation of the enzyme by K+.

The bovine lens neutral proteinase comprises a family of cysteine-dependent proteolytic activities

Inhibitor studies with peptide substrates demonstrate that bovine lens neutral proteinase comprises three distinct activities. Diisopropylfluorophosphate distinguishes the activity hydrolyzing carbobenzoxy-Gly-Gly-Leu-p-nitroanilide (inhibited) from that hydrolyzing carbobenzoxy-Leu-Leu-Glu-2-naphthylamide (not inhibited). Leupeptin inhibits hydrolysis of the substrate carbobenzoxy-Leu-Leu-Arg-2-naphthylamide, but not hydrolysis of carbobenzoxy-Gly-Gly-Leu-p-nitroanilide or carbobenzoxy-Leu-Leu-Glu-2-naphthylamide, demonstrating the presence of the third activity. Inhibition of the three activities by thiol reagents suggests that each activity may be dependent on an active-site cysteine residue.

Cloning and expression of multiple protein kinase C cDNAs

Three different protein kinase C related cDNA clones were isolated from a rat brain cDNA library and designated PKC-I, PKC-II, and PKC-III. These each encode very similar, but distinct, polypeptides that contain a region homologous with other protein kinases. COS cells transfected with either PKC-I or PKC-II specifically bind at least 5-fold more 3H-PDBu (phorbol ester) than control cells. An increase in Ca2+, phosphatidylserine, and diacylglycerol/phorbol-ester-dependent protein kinase activity is also observed in COS cells transfected with either PKC-I or PKC-II. The physiological implications of the discovery of three protein-kinase-C-related cDNAs are discussed.

GTPase center of elongation factor Tu is activated by occupation of the second tRNA binding site

Interaction of the elongation factor EF-Tu with the antibiotic kirromycin results in activation of the GTPase center of the factor and in induction of an additional tRNA binding site (tRNA binding site II to distinguish it from the classical tRNA binding site I). Activation of the GTPase center under these conditions is stimulated by addition of tRNA. Two-fold evidence is presented that this stimulation is due to tRNA binding to site II rather than to site I. First, a strong correlation is observed between stimulation of the GTPase activity and enhancement of the reactivity of Cys-81 of EF-Tu toward N-ethylmaleimide at various concentrations of aminoacyl-tRNA, deacylated tRNA, and N-acetylaminoacyl-tRNA. The latter effects signal tRNA binding to site II. Stimulation of the kirromycin-induced GTPase activity by tRNA binding to the factor also occurs when binding to site I is completely abolished. Such an abolishment was achieved by treating EF-Tu extensively with the thiol reagent L-1-tosylamido-2-phenylethyl chloromethyl ketone. EF-Tu X GTP thus treated has lost its ability to protect the ester bond of aminoacyl-tRNA. The relevance of these data for the sequence of events during protein synthesis and for control of translational fidelity is discussed.

Action of some pesticides on T4 to T3 conversion in cultured kidney and liver cells in the presence or absence of cysteine

The influence of aminotriazole (ATA), atrazine (ATZ), prometryne (P) and ATC on T4 to T3 conversion in kidney and liver cell cultures in the presence or absence of cysteine was studied. The experiment was carried out on cell cultures (rat renal cells and human embryo cells) and organotypic cultures (rat liver cells), treated with the above mentioned pesticides in 2 doses each, in the presence of 1 microgram and 10 micrograms T4 in the culture medium. This experiment was reproduced in the same conditions supplementing the culture medium with 30 mg cysteine per 100 ml culture medium. T3 and T4 in the culture medium were measured by RIA. The proteins in the monolayer cultures were also assayed. Cysteine proved to stimulate T4 to T3 conversion at the level of human and rat kidney cells with little variation depending on the pesticide and the dose applied. Between the activities of the human and the rat cells in the presence of the same pesticide, there were clear differences. The latter are also expressed in the values of proteic synthesis taking place in the renal human embryo cells and rat renal cell cultures under the same influences.

Characterisation in vivo of the reactive thiol groups of the lactose permease from Escherichia coli and a mutant; exposure, reactivity and the effects of substrate binding

The reactivity and accessibility of the reactive thiol groups of the native lactose permease and a mutant have been studied in a number of circumstances and with a number of reagents, in particular using the specific thiol-disulphide exchange reaction. Seven different reactive states of the thiol in the native protein have been characterised by their different second-order rate constants. Interconversion between these states is dependent on the magnitude of the protonmotive force, pH and substrate binding. In the absence of galactoside, reactivity is controlled by an ionisation with apparent pKa 9.3. This pKa is not affected by the protonmotive force, but it is lowered in the presence of external galactoside. The conformation adopted by the permease when in equilibrium with saturating galactoside appears to be different from that of the intermediate that accumulates during net turnover. In the former state, the reactivity of the thiol group is depressed, whereas in the latter state it is enhanced. The thiol group of the native protein is buried in a hydrophobic environment that has a dielectric constant considerably lower than that of water. The environment is not greatly perturbed by changes in the magnitude of the protonmotive force, but it is affected by the binding of galactoside. In a strain which carries the YUN mutation (Wilson, T.H. and Kusch, M. (1972) Biochim. Biophys. Acta 255, 786-797), two reactive thiols were characterised. The more reactive of the two is more exposed than the thiol group of the native molecule and is in an environment that has a dielectric constant close to that of water. The less reactive thiol appears to be more deeply buried than that of the native protein. Thus the mutation appears to produce a conformation change in the central portion of the polypeptide chain that results in greater exposure of the reactive thiol to the aqueous environment.

A case of hemoglobin Indianapolis [beta 112(G14) Cys----Arg] in an individual from Cordoba, Spain

Hemoglobin Indianapolis was first described by Adams et al (1,2) as a very unstable variant with a phenotype similar to severe beta-thalassemia. We have also characterized this variant, but there are several differences in the clinical expression of the variant described in our report and those described in the original case. We found Hb Indianapolis to be unstable, but not to the extent that it could not be detected by routine testing. The four family members heterozygous for the variant were not anemic, showed normal hematologic values, and did not exhibit any severe clinical disadvantages, although there was slight reticulocytosis. The variant could not be resolved from Hb A on cellulose acetate (pH 8.4), but isoelectric focusing showed a double band in the region of Hb A that is probably the variant and Hb A. However, the variant chain was clearly evident by globin chain analyses in acid and alkaline buffers. The condition of additional blood samples did not allow us to determine the oxygen dissociation properties of the variant or the rates of globin chain synthesis.

Collagenase activity in middle ear effusions

Collagenolytic enzyme activity has been demonstrated in middle ear effusions from patients suffering from otitis media with effusion. Collagenase activity was characterized using different biochemical techniques. Various chemical and physical parameters were titrated for optimal enzyme activity. Bivalent cations activated the enzyme with Ca2+ as the most potent activator. Chelators such as EDTA reduced the enzyme at low concentrations. The enzyme was found to have a higher specific activity in mucoid effusions than in serous and had characteristics similar to granulocyte derived collagenase from human leukocytes. Possible relationships between the presence of collagenase activity and tissue destruction in the middle ear after otitis media with effusion are discussed. The collagenase activity showed wide ranges within different categories of middle ear effusions.

Immune oxidative injury induced in mice exposed to normobaric O2: effects of thiol compounds on the splenic cell sulfhydryl content and Con A proliferative response

In vivo exposure of mice to normobaric O2 depresses the cellular immune response by a mechanism that remains unknown. In vitro oxidative injury leads to decreased sulfhydryl groups (SH) in lymphocytes. To determine whether in vivo exposure to O2 would have similar effects, we measured the SH content in spleen cells both from mice that had been exposed to normobaric O2 (O2 SC) and from controls exposed to ambient air (Air SC). The SH content of the fresh O2 SC was slightly decreased, whereas after 48 hr of culture, the SH content and the proliferative response of these cells were found to vary with the type and concentration of thiol or disulfide compounds added to the culture medium. Under standard culture conditions, i.e., RPMI 1640 medium containing 0.41 mM half-cystine, the SH content in O2 SC decreased sharply to about 10 and 20% that of Air SC in the absence or presence of Con A (2 micrograms/ml), respectively. Under these culture conditions, the proliferative response of O2 SC was 20.5% +/- 3.2 of Air SC. In cystine-free RPMI 1640 medium supplemented with various concentrations of L-cystine, L-cystine and 2-mercaptoethanol (2-ME), L-cysteine, or reduced glutathione (GSH), the proliferative response to Con A and the SH content of the O2 SC varied in parallel and were correlated (p less than 0.01). Half-cystine (0.41 mM) plus 2-ME (5 X 10(-5) M) or L-cysteine alone (4 mM) completely protected the SH content of O2 SC and induced a proliferative response 82% +/- 6 that of the controls. In cystine-free RPMI 1640 medium supplemented with GSH (4 mM), the SH content and proliferative response of O2 SC were 79 and 67.5% of Air SC, respectively. Other concentrations of these compounds were less effective. Oxygen scavengers such as SOD, catalase, mannitol, and vitamin E did not protect against the decrease of the O2 SC. The induced oxidative cellular damage might be related in part to a membrane lipid peroxidative process. These data show that in vivo exposure of mice to normobaric O2 induced lesions in splenic cells manifested under standard culture conditions by a decrease in both SH content and Con A proliferative response. The extent of these alterations could be modulated by variations of the thiol environment. Protection of the SH content correlated with protection of the proliferative response of the O2 SC.

Serine hydroxymethyltransferase from Escherichia coli: purification and properties

Serine hydroxymethyltransferase from Escherichia coli was purified to homogeneity. The enzyme was a homodimer of identical subunits with a molecular weight of 95,000. The amino acid sequence of the amino and carboxy-terminal ends and the amino acid composition of cysteine-containing tryptic peptides were in agreement with the primary structure proposed for this enzyme from the structure of the glyA gene (M. Plamann, L. Stauffer, M. Urbanowski, and G. Stauffer, Nucleic Acids Res. 11:2065-2074, 1983). The enzyme contained no disulfide bonds but had one sulfhydryl group on the surface of the protein. Several sulfhydryl reagents reacted with this exposed group and inactivated the enzyme. Spectra of the enzyme in the presence of substrates and substrate analogs showed that the enzyme formed the same complexes and in similar relative concentrations as previously observed with the cytosolic and mitochondrial rabbit liver isoenzymes. Kinetic studies with substrates showed that the affinity and synergistic binding of the amino acid and folate substrates were similar to those obtained with the rabbit liver isoenzymes. The enzyme catalyzed the cleavage of threonine, allothreonine, and 3-phenylserine to glycine and the corresponding aldehyde in the absence of tetrahydrofolate. The enzyme was also inactivated by D-alanine caused by the transamination of the active site pyridoxal phosphate to pyridoxamine phosphate. This substrate specificity was also observed with the rabbit liver isoenzymes. We conclude that the reaction mechanism and the active site structure of E. coli serine hydroxymethyltransferase are very similar to the mechanism and structure of the rabbit liver isoenzymes.

Dissociation of cysteine and glutathione levels from nitroglycerin-induced relaxation

The present study investigated possible involvement of cysteine (CSH) and reduced glutathione (GSH) as critical cellular sulfhydryls which mediate nitroglycerin (GTN)-induced cyclic GMP accumulation and relaxation in bovine coronary artery (BCA). Tolerance to the relaxant effects of GTN was induced in BCA in vitro by preincubation with 1 mM GTN for 2 h. GTN-tolerant BCA were at least 100-fold less sensitive than non-tolerant BCA to the relaxant effects of GTN. Consistent with a relationship between tolerance to both GTN-induced cyclic GMP accumulation and relaxation, cyclic GMP accumulation induced by 1 microM GTN was markedly reduced in GTN-tolerant BCA when compared with non-tolerant BCA. Incubation with 1 mM CSH for 1 h did not significantly alter GTN-induced cyclic GMP accumulation or relaxation in either GTN-tolerant or non-tolerant BCA. Levels of CSH, GSH and glutathione-disulfide (GSSG) were measured in non-tolerant BCA, GTN-tolerant BCA and GTN-tolerant BCA incubated with 1 mM CSH for 1 h. Levels of CSH and GSH were lower in GTN-tolerant BCA than in non-tolerant BCA, whereas GSSG levels were similar in both. In GTN-tolerant BCA incubated with 1 mM CSH, CSH levels were more than 10-fold above, and GSH levels were similar to corresponding values obtained in non-tolerant BCA. These data indicate that although incubation with CSH did not significantly reverse tolerance to GTN-induced cyclic GMP accumulation and relaxation in BCA, it did effectively raise the level of CSH and GSH in GTN-tolerant BCA, at least to corresponding levels found in non-tolerant BCA. These results indicate that the relaxant effects of GTN in BCA do not correlate with tissue levels of CSH and GSH. The findings do not support the hypothesis that CSH and GSH are the cellular sulfhydryls involved in mediating GTN-induced guanylate cyclase activation, cyclic GMP accumulation and relaxation in intact BCA.

Location in the yeast hexokinase structure of residues related to the enzyme activity

Seven residues implicated as acting directly in substrate binding in yeast hexokinase B have been identified in the crystallographic structure by chemical sequencing. The cysteine which is regarded as a residue critically maintaining the active conformation of yeast hexokinase has been selectively labelled and likewise located in the structure. In some parts of the amino acid sequence predicted from the high-resolution electron density map it is found that alignments of chemically sequenced peptides can be made unambiguously; however, the extent of matching to the predicted sequence varies considerably along the chain.

New biologic functions--selenium-dependent nucleic acids and proteins

Selenium occurs normally in living things as a highly specific component of certain enzymes and amino acid transfer nucleic acids (tRNAs). In bacteria, biosynthesis of essential selenoenzymes has been shown to be unaffected by wide variations in sulfur levels. The naturally occurring selenoenzymes so far identified from bacterial sources include glycine reductase, certain formate dehydrogenases, a hydrogenase, nicotinic acid hydroxylase, xanthine dehydrogenase and thiolase. The selenoenzyme, glutathione peroxidase, and three other selenoproteins of unknown function have been isolated from animals. In certain enzymes, e.g. glycine reductase, formate dehydrogenase, hydrogenase and glutathione peroxidase, the chemical form of selenium has been identified as selenocysteine. One enzyme, a bacterial thiolase, contains selenomethionine rather than selenocysteine. A labile, unidentified form of selenium is present in nicotinic acid hydroxylase, and by inference, xanthine dehydrogenase. The seleno-tRNAs serve as examples of a different type of biological macromolecule that is specifically modified with selenium. The major seleno-tRNAs in Clostridium sticklandii and Escherichia coli have been identified as glutamate and lysine isoaccepting species. The selenium-modified nucleoside is 5-methyl-aminomethyl-2-selenouridine (mnm5Se2U), which is the chemical analog of 5-methylaminomethyl-2-thiouridine, a previously identified minor base of E. coli tRNA2Glu. The seleno-tRNAGlu of C. sticklandii contains one gram atom of Se per mole of biologically active tRNA. Loss of Se from the modified nucleoside, mnm5Se2U, in this tRNA results in concomitant loss of glutamate charging activity suggesting that selenium is essential for interaction of the synthetase and its cognate tRNA.

Effects of variation in the dietary supply of cysteine and methionine on liver concentration of glutathione and "active sulfate" (PAPS) and serum levels of sulfate, cystine, methionine and taurine: relation to the metabolism of acetaminophen

Amounts of the sulfur-containing amino acids methionine and cysteine in synthetic diets were decreased from 22.8 mmol methionine (= 100 Met) and 26.4 mmol cysteine (= 100 Cys) per kilogram diet in the control group to (Met/Cys) 100:0, 75:0, 50:0, 25:0 and 25:25, respectively, in experimental diet groups, in order to evaluate effects of limiting sulfur supply on the availability of cosubstrates for conjugation. Below a Met level of 22.8 mmol/kg growth rates decreased. Urinary excretion of inorganic sulfate decreased to 10-20% of control values in all groups. Feeding diets 100:0 and 75:0 for 14 days resulted in a decrease of the concentration of inorganic sulfate in serum; on diets 25:25 and 25:0 an increase was found. A decreased content of methionine/cysteine resulted in an increase in cystine, a decrease in taurine and no change in methionine concentration in serum. In all experimental groups the glutathione concentration in the liver diminished to about 20% of control values, and the hepatic concentration of "active sulfate" (PAPS: adenosine 3'-phosphate 5'-phosphosulfate) decreased in most rats. At the lowest methionine supply, sulfate conjugation of acetaminophen decreased to 50% of control. The formation of the acetaminophen glutathione conjugate remained unaffected, in spite of a decreased hepatic glutathione availability.

Effect of metal ions on the structure and activity of calcium-activated neutral protease (CANP)

To clarify the mechanism of activation of calcium activated neutral protease (CANP, or mCANP: active at mM Ca2+), the structure of mCANP was examined by measuring CD spectra and by titration of SH groups in the presence of Mn2+. Mn2+ significantly increases the sensitivity of CANP to Ca2+ but CANP is not active with Mn2+ alone. The structural changes induced by Mn2+ were compared with those induced by Ca2+, and the structure of muCANP, which is active at microM Ca2+, was also examined for comparison. Mn2+ and Ca2+ induced the same structural changes of CANP. However, specific activation of the active site SH group by Ca2+ was not observed with Mn2+. Six moles of calcium bound to mCANP and the average dissociation constant of Ca2+ was 150 microM. The structure of muCANP was similar to that of mCANP in terms of the CD spectra. The titration of SH groups of muCANP indicated that the structure of muCANP was looser or SH groups were more exposed than in the case of mCANP. A model which can explain the activation of mCANP is proposed and the mechanism of activation is discussed based on the proposed model. The role of Ca2+ can be explained in terms of conformational change and activation of the active-site SH group of CANP.

Chemical modifications of the sigma subunit of the E. coli RNA polymerase

The function of arginine, cysteine and carboxylic amino acid (glutamic and aspartic) residues of sigma was studied using chemical modification by group specific reagents. Following modification of 3 arginine residues with phenylglyoxal or 3 cysteine residues with N-ethylmaleimide (NEM) sigma activity was lost. Analysis of the kinetic data for inactivation indicated that one arginine or cysteine residue is essential for sigma activity. At low NEM concentration alkylation was limited to a non-critical cysteine which was identified as cysteine-132. Modification of arginine or cysteine residues had no observable effect on the binding of the inactivated sigma to the core polymerase. Modification of aspartic and/or glutamic acid residues with the water-soluble carbodiimides 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide hydrochloride (EDC) or 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide metho-p-toluene sulfonate (CMC) resulted in loss of sigma activity. The inactivation data indicated that one carboxylic amino acid residue is essential for sigma activity. Sigma modified with EDC, CMC or EDC in the presence of glycine was inactive in supporting promoter binding and initiation by core polymerase. Reaction with EDC plus (3H)glycine resulted in the incorporation of glycine into sigma. The (3H)glycine-sigma was unable to form a stable holoenzyme complex.

Contractile activities of several cysteine-containing leukotrienes in the guinea-pig lung strip

Eight biosynthetically formed cysteine-containing leukotrienes dose dependently (0.01-100 nM) contracted parenchymal strips of guinea-pig lung. The response to the leukotrienes was slow in onset, remarkably long-lasting and often tachyphylactic upon repeated administration. All the leukotrienes (LTC3, 8,9-LTC3, LTC4, 11-trans-LTC4, LTC5, LTD4, LTE4 and 11-trans-LTE4) were equally active full agonists for contraction, but approximately 5000 times as potent as histamine on a molar basis. Radiolabelled leukotriene C was insignificantly metabolized during the assay of contractile activity, indicating that the leukotrienes were active per se. The equipotency of LTC4, LTD4 and LTE4 also indicates that each of these three major constituents of slow reacting substance of anaphylaxis (SRS-A), may be considered a significant mediator of allergen-induced bronchoconstriction. In addition, the closely similar contractile activity of glutathionyl-substituted leukotrienes derived from polyunsaturated fatty acids other than arachidonic acid, suggests that they may contribute to bronchospastic disease under pathological and nutritional conditions promoting their formation.