Two-dimensional thin-layer methods

Proteolysis of caseins and the proteose-peptone fraction of bovine milk

The proteolysis of highly purified samples of αs1-, αs2-, β-and κ-caseins by porcine plasmin and by bovine plasminogen with urokinase has been examined principally by gel electrophoresis. The resulting peptide band patterns were compared with those of total proteose-peptone (TPP) samples prepared from fresh and stored raw and pasteurized milk, and also with those obtained during the natural course of proteolysis by indigenous enzymes in milk during storage. TPP was found to contain at least 38 components detectable by a single electrophoresis run. Apart from residual traces of whey proteins and intact caseins nearly all of these components were fragments of caseins produced by indigenous plasmin, with products from the breakdown of αs1- and β-casein predominating. Over 90 % of TPP has been accounted for in this way. A fragment consisting of residues 29–105 of β-casein was isolated and characterized from both stored milk and from plasmin digests of β-casein. This fragment was a relatively major product of the natural proteolysis occurring during storage of milk, but contrary to a report in the literature it was not the same as proteose-peptone component 8-slow. Since many of the components of TPP resulted from proteolysis, the composition of TPP was found to vary according to the time and temperature of storage of the milk from which it was prepared. Thus, while the proteose-peptone fraction of milk can easily be defined operationally it cannot be rigorously defined in terms of its composition unless the history of the milk is also defined.

The effect of histamine and cyclic adenosine monophosphate on myosin light chain phosphorylation in human umbilical vein endothelial cells

Histamine causes adjacent endothelial cells to retract from each another. We examined phosphorylation of the 20-kD myosin light chain (MLC20) in human umbilical vein endothelial cells (HUVECs) exposed to histamine to determine if we could find evidence to support the hypothesis that retraction of these cells in response to histamine represents an actomyosin-initiated contraction of the endothelial cytoskeleton. We found that MLC20 in HUVECs was constitutively phosphorylated with approximately 0.2 mol phosphate/mol MLC20. Histamine increased MLC20 phosphorylation by 0.18 +/- 0.05 mol phosphate/mol MLC20. This peak increase in phosphorylation occurred 30 s after initiating histamine exposure, persisted through 90s, and returned to control levels by 5 min. Agents that increase HUVEC cAMP prevent cell retraction in response to histamine. An increase in HUVEC cAMP decreased MLC20 phosphorylation by 0.18 +/- 0.02 mol phosphate/mol MLC20 and prevented the increase in MLC20 phosphorylation after exposure to histamine. Tryptic peptide maps of phosphorylated myosin light chain indicated that myosin light chain kinase phosphorylated MLC20 in HUVECs under basal, cAMP-, and histamine-stimulated conditions. Phosphoaminoacid analysis of the monophosphorylated peptide indicated that, in contrast to smooth muscle cells, ser19 and thr18 monophosphorylation occurs in HUVECs. On the basis of our results, modulation of myosin light chain kinase activity may be an important regulatory step in the control of endothelial barrier function.

Preparation and characterization of spin-labeled derivatives of epidermal growth factor (EGF) for investigations of the interactions of EGF with its receptor by electron paramagnetic resonance spectroscopy

We prepared, purified, and characterized derivatives of epidermal growth factor (EGF) having a nitroxide spin-label attached covalently at the amino terminus. Characterization of these derivatives with regard to the positions of attachment of the spin-label was accomplished by a combination of peptide mapping, protein sequencing, and fast atom bombardment-mass spectrometry. One derivative was chosen for use in initial investigations by electron paramagnetic resonance (EPR) spectroscopy of receptor-bound EGF and its dissociation kinetics. This derivative was found to be equipotent with the native hormone in competitive binding assays, in activating the EGF receptor kinase, and in stimulating the formation of EGF receptor dimers in solubilized cell extracts. Upon binding to solubilized EGF receptor, the spin-labeled EGF derivative became immobilized, giving rise to a visually distinct slow-motion EPR spectrum. The resulting spectrum showed no detectable dipolar interaction between nitroxides, indicating that the nitroxide moieties of spin-labels reacted at the amino termini of receptor-bound spin-labeled EGF molecules are separated by a distance of at least 16 A. An EPR study of the kinetics of dissociation of spin-labeled EGF in the presence of excess unlabeled EGF revealed a rapid component with a k off approximately 2 x 10(-2) s-1 and a less well resolved slow component.

Identification of phosphorylation sites for adenosine 3',5'-cyclic phosphate dependent protein kinase on the voltage-sensitive sodium channel from Electrophorus electricus

The voltage-sensitive sodium channel from the electroplax of Electrophorus electricus is selectively phosphorylated by the catalytic subunit of cyclic-AMP-dependent protein kinase (protein kinase A) but not by protein kinase C. Under identical limiting conditions, the protein was phosphorylated 20% as rapidly as the synthetic model substrate kemptamide. A maximum of 1.7 +/- 0.6 equiv of phosphate is incorporated per mole. Phosphoamino acid analysis revealed labeled phosphoserine and phosphothreonine at a constant ratio of 3.3:1. Seven distinct phosphopeptides were identified among tryptic fragments prepared from radiolabeled, affinity-purified protein and resolved by HPLC. The three most rapidly labeled fragments were further purified and sequenced. Four phosphorylated amino acids were identified deriving from three consensus phosphorylation sites. These were serine 6, serine 7, and threonine 17 from the amino terminus and a residue within 47 amino acids of the carboxyl terminus, apparently serine 1776. The alpha-subunits of brain sodium channels, like the electroplax protein, are readily phosphorylated by protein kinase A. However, these are also phosphorylated by protein kinase C and exhibit a markedly different pattern of incorporation. Each of three brain alpha-subunits displays an approximately 200 amino acid segment between homologous repeat domains I and II, which is missing from the electroplax and skeletal muscle proteins [Noda et al. (1986) Nature (London) 320, 188; Kayano et al. (1988) FEBS Lett. 228, 1878; Trimmer et al. (1989) Neuron 3, 33]. Most of the phosphorylation of the brain proteins occurs on a cluster of consensus phosphorylation sites located in this segment. This contrasts with the pattern of highly active sites on the amino and carboxyl termini of the electroplax protein. The detection of seven labeled tryptic phosphopeptides compared to the maximal labeling stoichiometry of approximately 2 suggests that many of the acceptor sites on the protein may be blocked by endogenous phosphorylation.

Primary structure of prostaglandin G/H synthase from sheep vesicular gland determined from the complementary DNA sequence

Prostaglandin G/H synthase (8,11,14-icosatrienoate, hydrogen-donor:oxygen oxidoreductase, EC 1.14.99.1) catalyzes the first step in the formation of prostaglandins and thromboxanes, the conversion of arachidonic acid to prostaglandin endoperoxides G and H. This enzyme is the site of action of nonsteroidal anti-inflammatory drugs. We have isolated a 2.7-kilobase complementary DNA (cDNA) encompassing the entire coding region of prostaglandin G/H synthase from sheep vesicular glands. This cDNA, cloned from a lambda gt 10 library prepared from poly(A)+ RNA of vesicular glands, hybridizes with a single 2.75-kilobase mRNA species. The cDNA clone was selected using oligonucleotide probes modeled from amino acid sequences of tryptic peptides prepared from the purified enzyme. The full-length cDNA encodes a protein of 600 amino acids, including a signal sequence of 24 amino acids. Identification of the cDNA as coding for prostaglandin G/H synthase is based on comparison of amino acid sequences of seven peptides comprising 103 amino acids with the amino acid sequence deduced from the nucleotide sequence of the cDNA. The molecular weight of the unglycosylated enzyme lacking the signal peptide is 65,621. The synthase is a glycoprotein, and there are three potential sites for N-glycosylation, two of them in the amino-terminal half of the molecule. The serine reported to be acetylated by aspirin is at position 530, near the carboxyl terminus. There is no significant similarity between the sequence of the synthase and that of any other protein in amino acid or nucleotide sequence libraries, and a heme binding site(s) is not apparent from the amino acid sequence. The availability of a full-length cDNA clone coding for prostaglandin G/H synthase should facilitate studies of the regulation of expression of this enzyme and the structural features important for catalysis and for interaction with anti-inflammatory drugs.

Human red cell acid phosphatase (ACP1): evidence for differences in the primary structure of the two isozymes encoded by the ACP1*B allele

Molecular properties of the two isozymes expressed by the B allele at the red cell acid phosphatase locus (ACP1) have been studied to distinguish between possible mechanisms for their production. The difference in electric charge exhibited by the native isozymes was retained under denaturing conditions; the unfolded peptide chains renatured without conversion of one form to the other. Chromatographic analysis [thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC)] of tryptic digests showed 12 peptides common to both isozymes but also revealed 5 peptides unique to one isozyme and 3 (possibly 4) peptides unique to the other. These findings argue against both conformational isomerization and simple posttranslational modification as the mechanism of generation of the two isozymes. We suggest that the two isozymes are synthesized as discrete molecular entities.

Purification and characterization of the Danish (Skive) variant of mouse liver alcohol dehydrogenase

The partially inbred Danish (Skive) strain of mice exhibits a form of liver alcohol dehydrogenase (ADH) which differs in electrophoretic mobility from that of all other inbred mouse strains thus far examined, e.g., C57BL/10, DBA/2J, and BALB/c. In order to compare the catalytic and molecular properties of the "variant" and "normal" enzyme forms, they were purified to homogeneity by ion-exchange and affinity chromatography. Tryptic peptides of reduced and carboxymethylated subunits of the normal and variant ADH forms were mapped by thin-layer two-dimensional electrophoresis and chromatography and by reversed-phase high-performance liquid chromatography. A unique nonapeptide in the Danish mouse liver ADH which did not appear in enzymes from C57BL/10, DBA/2J, or BALB/c mice was identified by both methods. Amino acid sequencing of this peptide revealed that the Arg residue at position 124, as predicted from the cDNA sequence of ADH in DBA/2J mice, has been replaced by Leu in the Danish variant. The Leu for Arg substitution in the variant form appears to account for its decreased cathodic mobility with electrophoresis in starch gels at pH 7.2. The Km and Vmax of ADH from the Danish strain for three primary alcohols and three aldehydes were similar in value to those of ADH from the C57BL/10, DBA/2J, and BALB/c strains. Based on the X-ray structure of horse liver ADH, position 124 is on the solvent-exposed surface of the catalytic domain. The finding that the kinetic constants are similar for the normal and variant forms is consistent with the observation that this residue is not in the active site and that there is no known role for it in the ADH catalytic mechanism.

Purification and properties of an endospermic protein of maize associated with the Opaque-2 and Opaque-6 genes

Maize endosperms accumulate during development a large amount of storage proteins (zeins). The rate of zein accumulation is under the control of several regulatory genes. Two of these, the opaque-2 and opaque-6 mutants, lower the zein level, thus improving the nutritional quality of maize meals. An endosperm protein of Mr 32 000 (b-32) appears to be correlated with the zein level. The b-32 protein is encoded by the opaque-6 gene which, in turn, is activated by opaque-2. We report the purification, amino-acid composition and peptide map of b-32 protein. Furthermore we demonstrate that the protein exists as a monomer likely located in the soluble cytoplasm. As a step towards the isolation of a complementary-DNA clone for b-32 protein, the purification of its corresponding mRNA is described.

Nonhistone protein BA is a glutathione S-transferase localized to interchromatinic regions of the cell nucleus

A DNA-binding nonhistone protein, protein BA, was previously demonstrated to co-localize with U-snRNPs within discrete nuclear domains (Bennett, F. C., and L. C. Yeoman, 1985, Exp. Cell Res., 157:379-386). To further define the association of protein BA and U-snRNPs within these discrete nuclear domains, cells were fractionated in situ and the localization of the antigens determined by double-labeled immunofluorescence. Protein BA was extracted from the nucleus with the 2.0 M NaCl soluble chromatin fraction, while U-snRNPs were only partially extracted from the 2.0 M NaCl-resistant nuclear structures. U-snRNPs were extracted from the residual nuclear material by combined DNase I/RNase A digestions. Using an indirect immunoperoxidase technique and electron microscopy, protein BA was localized to interchromatinic regions of the cell nucleus. Protein BA was noted to share a number of chemical and physical properties with a family of cytoplasmic enzymes, the glutathione S-transferases. Comparison of the published amino acid composition of protein BA and glutathione S-transferases showed marked similarities. Nonhistone protein BA isolated from saline-EDTA nuclear extracts exhibited glutathione S-transferase activity with a variety of substrates. Substrate specificity and subunit analysis by SDS polyacrylamide gel electrophoresis revealed that it was a mixture of several glutathione S-transferase isoenzymes. Protein BA isolated from rat liver chromatin was shown by immunoblotting and peptide mapping techniques to be two glutathione S-transferase isoenzymes composed of the Yb and Yb' subunits. Glutathione S-transferase Yb subunits were demonstrated to be both nuclear and cytoplasmic proteins by indirect immunolocalization on rat liver cryosections. The identification of protein BA as glutathione S-transferase suggests that this family of multifunctional enzymes may play an important role in those nuclear domains containing U-snRNPs.

Suicide inhibition as a likely cause of variable specific activity in trimethylamine dehydrogenase from bacterium W3A1

Trimethylamine hydrogenase isolated from bacterium W3A1 grown on dimethylamine was of variable, but low specific activity and had modified spectral properties. Chemical analyses for Fe, S and P indicated that the [4Fe-4S] clusters of the modified enzyme are intact and that the covalently bound flavin is probably present, but in modified form. A peptide with absorbance maximum at 358 nm and fluorescence excitation and emission maxima in dimethylformamide at 358 nm and 495 nm, respectively, was isolated by gel chromatography and HPLC of tryptic peptides of acetamidylated, modified trimethylamine dehydrogenase. These spectral properties are similar to those of 4a- or 5a-substituted flavins and suggest that the enzyme had been modified by in vivo reaction with a suicide inhibitor. This inhibitor, or a compound giving rise to it, seems to be present in a commercial source of dimethylamine.

Isolation of a Bacillus stearothermophilus mutant exhibiting increased thermostability in its restriction endonuclease

A procedure was developed for the selection of spontaneous mutants of Bacillus stearothermophilus NUB31 that are more efficient than the wild type in the restriction of phage at elevated temperatures. Inactivation studies revealed that two mutants contained a more thermostable restriction enzyme and one mutant contained three times more enzyme than the wild type. The restriction endonucleases from the wild type and one of the mutants were purified to apparent homogeneity. The mutant enzyme was more thermostable than the wild-type enzyme. The subunit molecular weight, amino acid composition, N-terminal and C-terminal amino acid residues, tryptic peptide map, and catalytic properties of the two enzymes were determined. The two enzymes have similar catalytic properties, but the molecular size of the mutant enzyme is approximately 6 to 7 kilodaltons larger than that of the wild-type enzyme. The mutant enzyme contains 54 additional amino acid residues, of which 26 to 28 are aspartate/asparagine, 8 to 15 are glutamate/glutamine, and 8 to 9 are tyrosine residues. The two enzymes contained similar amounts of the other amino acids, identical N-terminal residues, and different C-terminal residues. Tryptic peptide analyses revealed a high degree of homology between the two enzymes. The increased thermostability observed in the mutant enzyme appears to have been achieved by a mutation that resulted in the addition of amino acid residues to the wild-type enzyme. A number of mechanisms are discussed that could account for the observed difference between the mutant and wild-type enzymes.

Superoxide dismutase in Drosophila melanogaster. Mutation site difference between two electromorphs

Two electrophoretically distinguishable variants of superoxide dismutase (SOD) are common in natural populations of Drosophila melanogaster. We have earlier comparatively characterized these two electromorphs, SODF and SODS. By peptide mapping in high-performance liquid chromatography (HPLC), we now show that the difference between the two electromorphs is due to the replacement of Asn-96 (SODF) by Lys-96 (SODS). It is far from clear how this replacement causes the biochemical differences (in thermostability, specific activity, and others) observed between these two forms of the enzyme.

Chemical modification of dopamine beta-hydroxylase

Dopamine beta-hydroxylase (3,4- dihydroxyphenylethylamine ,ascorbate:oxygen oxidoreductase (beta-hydroxylating), EC 1.14.17.1) is the terminal enzyme in the biosynthetic pathway of norepinephrine. Chemical modification studies of this enzyme were executed to investigate contributions of specific amino-acid side-chains to catalytic activity. Sulfhydryl reagents were precluded, since no free cysteine residue was detected upon titration of the denatured or native protein with 2-chloromercuri-4-nitrophenol. Incubation of enzyme with diazonium tetrazole caused inactivation of the protein coupled with extensive reaction of lysine and tyrosine residues. Reaction with iodoacetamide resulted in complete loss of enzymatic activity with reaction of approximately three histidine residues; methionine reaction was also observed. Modification of the enzyme using diethylpyrocarbonate resulted in complete inactivation of the enzyme, and analysis of the reacted protein indicated a loss of approx. 1.7 histidine residues per protein monomer with no tyrosine or lysine modification observed. The correlation of activity loss with histidine modification supports the view that this residue participates in the catalytic function of dopamine beta-hydroxylase.

Structural comparison of lactate dehydrogenase homologs differing in sensitivity to hydrostatic pressure

The muscle-type (M4) lactate dehydrogenases (L-lactate: NAD+ oxidoreductase EC 1.1.1.27) of two teleost fishes, Sebastolobus alascanus and Sebastolobus altivelis , differ in the susceptibility of ligand binding to perturbation by moderate hydrostatic pressures. The enzyme homologs were purified by affinity chromatography. The amino-acid compositions of these enzymes are virtually identical. The proteins were digested with trypsin and the peptide mixtures mapped using reverse-phase HPLC. Although there was variation in elution times of some peaks, the amino-acid compositions of the fractions from the two profiles were highly similar. Only one clear difference in amino-acid composition was found and this peptide was sequenced using the manual dansyl-Edman method. The enzyme of S. alascanus , which is susceptible to pressure-perturbation, had a histidine at position 115; the S. altivelis enzyme had an asparagine. Ionization of histidine is affected by pressure and may be involved in the differences between the two lactate dehydrogenase homologs. There is no covalently bound phosphate associated with either enzyme, and thus phosphorylation cannot account for the differences between the enzyme homologs. Acquisition of pressure-tolerance appears to involve only minor changes in primary structure.

Purification and characterization of mouse alcohol dehydrogenase from two inbred strains that differ in total liver enzyme activity

Alcohol dehydrogenase activity in mouse liver homogenate-supernatants is 1.7 times greater in the C57BL/10 strain than in the BALB/c strain, regardless of whether activity is expressed in units per gram liver, total liver, or milligram DNA. The Km values for ethanol and NAD+, approximately 0.4 and 0.03 mM, respectively, of enzyme purified from both strains are similar. Moreover, the Ki for NADH, 1 microM, the pH optimum for ethanol oxidation, 10.5, and the Vmax for ethanol oxidation, 160 min-1, for ADH from the C57BL/10 and BALB/c strains are similar. Therefore, the difference in ADH activity in the two strains cannot be due to differences in the catalytic properties of the enzyme. The electrophoretic and isoelectric focusing patterns and two-dimensional tryptic peptide maps of the purified enzyme from both strains are identical. Thus the amino acid sequences of enzyme from C57BL/10 and BALB/c mice must also be identical or very similar. The difference in ADH activity in the two strains is most likely the result of genetic differences in the content of ADH protein in liver.

Comparison of the D-lactate stereospecific dehydrogenase of Limulus polyphemus with active-site regions of L-lactate dehydrogenases

Lactate dehydrogenase (D-lactate:NAD+ oxidoreductase, EC 1.1.1.28) from the horseshoe crab, Limulus polyphemus, a dimeric enzyme stereospecific for D-lactate, has been purified by affinity chromatography. Maleyl tryptic peptides containing arginine residues isolated from the Limulus enzyme have been characterized and sequenced. The small peptides obtained from similarly treated L-lactate-specific enzyme homologs define major portions of the substrate and coenzyme binding regions and are virtually identical among L-lactate-specific enzymes. Although the six small peptides and free arginine isolated from the Limulus enzyme indicate that the small number of arginine tryptic peptides are located in a few discrete consecutive clusters similarly to the L-lactate dehydrogenases, the peptides nevertheless show no obvious sequence homology to the corresponding peptides from L-lactate dehydrogenases. These results indicate that this lactate dehydrogenase of altered substrate specificity either evolved with major rearrangements of the active site if it evolved from an L-lactate dehydrogenase, or that D-lactate dehydrogenases have evolved from a different protein. The results contradict proposed models which suggest that minor changes in the spatial orientation of pyruvate resulting from minimal rearrangement of the active site could accommodate the change in substrate specificity.

Regulation of yeast phosphorylase by phosphorylase kinase and cAMP-dependent protein kinase

Yeast phosphorylase is phosphorylated and activated by a cyclic AMP-independent protein kinase (called phosphorylase kinase) and a cyclic AMP-dependent protein kinase. Only in the presence of both kinases is phosphorylase fully activated and phosphorylated. No evidence was found for the presence of two phosphorylation sites as an identical phosphopeptide pattern of phosphorylase is obtained after phosphorylation by either one or both kinases. The kinases probably phosphorylate identical sites but recognize different subunits of phosphorylase. Phosphorylase kinase phosphorylates the high-Mr subunit while cAMP-dependent protein kinase phosphorylates the low-Mr subunit.

Interaction of F1-ATPase, from ox heart mitochondria with its naturally occurring inhibitor protein. Studies using radio-iodinated inhibitor protein

The ox heart mitochondrial inhibitor protein may be iodinated with up to 0.8 mol 125I per mol inhibitor with no loss of inhibitory activity, with no change in binding affinity to submitochondrial particles, and without alteration in the response of membrane-bound inhibitor to energisation. Tryptic peptide maps reveal a single labelled peptide, consistent with modification of the single tyrosine residue of the protein. A single type of high-affinity binding site (Kd=96 . 10 (-9)M) for the inhibitor protein has been measured in submitochondrial particles. The concentration of this site is proportional to the amount of membrane-bound F1, and there appears to be one such site per F1 molecule. The ATp hydrolytic activity of submitochondrial particles is inversely proportional to the occupancy of the high-affinity binding site for the inhibitor protein. No evidence is found for a non-inhibitory binding site on the membrane or on other mitochondrial proteins. In intact mitochondria from bovine heart, the inhibitor protein is present in an approx. 1:1 ratio with F1. Submitochondrial particles prepared by sonication of these mitochondria with MgATP contain about 0.75 mol inhibitor protein per mol F1, and show about 25% of the ATPase activity of inhibitor-free submitochondrial particles. Additional inhibitor protein can be bound to these particles to a level of 0.2 mol/mol F1, with consequent loss of ATPase activity. If MgATP is omitted from the medium, or inhibitors of ATP hydrolysis are present, the rate of combination between F1 and its inhibitor protein is very much reduced. The equilibrium level of binding is, however, unaltered. These results suggest the presence of a single, high-affinity, inhibitory binding site for inhibitor protein on membrane-bound F1. The energisation of coupled submitochondrial particles by succinate oxidation or by ATP hydrolysis results in both the dissociation of inhibitor protein into solution, and the activation of ATP hydrolysis. At least 80% of the membrane-bound F1-inhibitor complex responds to this energisation by participating in a new equilibrium between bound and free inhibitor protein. This finding suggests that a delocalised energy pool is important in promoting inhibitor protein release from F1. Dissipation of the electrochemical gradient by uncouplers, or the binding of oligomycin or efrapetin effectively blocks energised release of the inhibitor protein. Conversely, the addition of aurovertin or adenosine 5'--[beta, lambda--imido]triphosphate enhances energy-driven release. The mode of action of various inhibitors on binding and energised release of the protein inhibitor is discussed.

A new isotype sequence (V kappa 27) of the variable region of kappa-light chains from a mouse hybridoma-derived anti-(streptococcal group A polysaccharide) antibody containing an additional cysteine residue. Application of the dimethylaminoazobenzene isothiocyanate technique for the isolation of peptides

The first complete sequence of the variable region of a kappa-light chain (V kappa) from a mouse anti-(streptococcal group A polysaccharide) antibody (immunoglobulin 7S34.1) is reported. Immunoglobulin 7S34.1 was isolated from the ascitic fluid of hybridoma 7S34.1 previously cloned in vitro. A newly developed technique for the isolation of peptides by using pre-column formation of peptide derivatives with dimethylaminoazobenzene isothiocyanate also served to complete the sequence. The sequence of the variable region of the kappa-light chain of immunoglobulin 7S34.1 defines a new mouse V kappa isotype (V kappa 27) and is the first mouse immunoglobulin light-chain variable region to be shown to have an extra cysteine residue at position 48.

Purification and characterization of a cysteine dioxygenase from the yeast phase of Histoplasma capsulatum

A cysteine dioxygenase, cysteine oxidase (EC 1.13.11.20), has been purified from the cytosolic fraction of yeast phase cells of the dimorphic fungus Histoplasma capsulatum. The cysteine oxidase is an iron-containing dioxygenase with a molecular weight of 10500 (+/- 1500) and is present only in the yeast phase of the fungus. The enzyme is highly specific for L-cysteine, with a Km of 2 X 10(-5) M in vitro. The product of cysteine oxidation is cysteinesulfinic acid, as analyzed by thin-layer chromatography and mass spectroscopy. To our knowledge, this is the first cysteine oxidase isolated from a fungus, and it probably plays an important role in the mycelial to yeast phase transition of H. capsulatum during which redox potential and cysteine levels are crucial factors.

Complete amino acid sequences of two protease inhibitors in the venom of Bungarus fasciatus

Two analogous protease inhibitors, VIIIb and IX in the venom of Bungarus fasciatus were reduced and carboxymethylated. Tryptic peptides were separated by cellulose thin-layer peptide mapping technique, and amino acid sequences were analyzed by DABITC/PITC double coupling method. Alignment of all tryptic peptides was established by analyses of chymotryptic peptides and further confirmed by Staphylococcus aureus V8 protease digestion. IX consisted of 65 amino acid residues. VIIIb consisted of 62 residues, identical to the N-terminal 62-amino acid sequence of IX.

Comparisons of highly purified hepatic microsomal cytochromes P-450 from Holtzman and Long-Evans rats

The present study describes the purification and characterization of strain variant forms of a major phenobarbital-inducible microsomal hemoprotein, cytochrome P-450b, from Holtzman and Long-Evans rats. The strain variant hemoproteins cannot be resolved by sodium dodecyl sulfate gel electrophoresis, but can be partially separated in two-dimensional isoelectric focusing SDS gels. If, however, sodium tetradecyl sulfate is incorporated into the one-dimensional gel system, separation of the cytochromes P-450b is achieved. Minor structural differences are detected in the peptides of the cytochromes P-450b following limited proteolysis by Staphylococcus aureus V8 protease, cleavage by cyanogen bromide, or reverse-phase high-pressure liquid chromatography of tryptic peptides. The strain variant cytochromes P-450b are immunochemically and spectrally indistinguishable. The optical spectra of the ferric and ferrous hemoproteins are identical, as are the CO- and ethylisocyanide-reduced difference spectra. Ferrous cytochromes P-450b from both rat strains effectively bind metyrapone with equivalent affinities. In addition, the cytochromes P-450b do not differ in their catalytic activities toward benzphetamine, hexobarbital, benzo [a]pyrene, zoxazolamine, 7-ethoxycoumarin, estradiol-17 beta and testosterone. Cytochrome P-450c, the predominant isozyme inducible in rat liver by 3-methylcholanthrene, was purified from Holtzman and Long-Evans rats. Cytochromes P-450c from both rat strains are indistinguishable based on electrophoretic, immunological, spectral and catalytic properties. Minor structural differences in the cytochromes P-450c were revealed in the reverse-phase high-pressure liquid chromatographic profiles of the tryptic peptides of these hemoproteins, but not in the peptides generated by limited proteolysis or cleavage with cyanogen bromide.

Cobra venom acetylcholinesterase: nature of charge isoforms

Charge isoforms of cobra (Naja naja oxiana) venom acetylcholinesterase, separated by isoelectric focusing, differ only by the number of free carboxyl groups of glutamic and/or aspartic acid side-chains in the enzyme molecule. The isoforms appear to be produced by a post-translational deamidation of accessible glutamin and/or asparagine residues. The isoforms have identical catalytic specificities towards characteristic acetylcholinesterase substrates.