Critical values for testing the significance of amino acid composition indexes

Structural diversity and differential light control of mRNAs coding for angiosperm glyceraldehyde-3-phosphate dehydrogenases

Subunits A and B of chloroplast glyceraldehyde-3-phosphate dehydrogenase are synthesized as higher molecular weight precursors when polyadenylylated mRNA from angiosperm seedlings is translated in vitro by wheat germ ribosomes. The in vivo levels of mRNA coding for these precursors are strongly light dependent, and the increase in translational activity stimulated by continuous white light, relative to dark-grown seedlings, is at least 5- to 10-fold for the seven plant species investigated. As opposed to this, light does not seem to change mRNA levels coding for cytosolic glyceraldehyde-3-phosphate dehydrogenase, and the polypeptides synthesized in vitro have the same size as the authentic subunits. In addition, precursors of the chloroplast enzyme were identified for 12 different angiosperm species and compared with their respective subunits synthesized in vivo. The patterns of the in vitro and in vivo products correlate in several major characteristics. They both display a remarkable interspecific heterogeneity with respect to size and number of polypeptides. The peptide extensions of the enzyme precursors calculated from these data vary between 4,000 and 12,000 daltons and seem to fall into three major size classes. The present data demonstrate that chloroplast glyceraldehyde-3-phosphate dehydrogenase, like its cytosolic counterpart, is encoded in the nucleus. Yet, the two dehydrogenases are controlled differently at both the ontogenetic and phylogenetic levels. They follow separate biosynthetic pathways with respect to light regulation, post-translational processing, and transport and also exhibit different evolutionary rates. The fast evolutionary change observed for the chloroplast enzyme contrasts sharply with the conservative structure and sequence of the cytosolic enzyme.

High sensitivity analysis of proteins and peptides by capillary electrophoresis-tandem mass spectrometry: recent developments in technology and applications

Analytical biochemistry, in particular the analysis of regulatory proteins that control biological systems and pathways, is dependent on methods of ever-increasing sensitivity. Capillary electrophoresis (CE) has long been recognized as an ultrasensitive analytical technique. In spite of the high sensitivity, CE has not penetrated protein discovery research as a standard analytical method. In this review article we summarize recent technical developments which have significantly enhanced CE as a tool for the analysis of trace amounts of proteins. Specifically, we review recent advances in the development and application of capillary electrophoresis-mass spectrometry (CE-MS) and on-line analyte concentration techniques, and introduce the emerging field of microfluidics as a front end to mass spectrometry (MS).

Purification and properties of membrane-bound aminopeptidase P from rat lung

The membrane-bound form of aminopeptidase P (aminoacylprolyl-peptide hydrolase) (EC 3.4.11.9) was purified 670-fold to apparent homogeneity from rat lung microsomes. The enzyme was solubilized from the membranes using a phosphatidylinositol-specific phospholipase C. The purification scheme also resulted in homogeneous preparations of dipeptidylpeptidase IV (EC 3.4.14.5) and membrane dipeptidase (EC 3.4.13.19). Aminopeptidase P had a subunit molecular weight of 90,000, which included at least 17% N-linked carbohydrate. The molecular weight by gel permeation chromatography varied from 220,000 to 340,000, depending on the conditions used. The amino acid composition was determined and the N-terminal sequence was found to be X1-Gly2-Pro3-Glu4-Ser5-Leu6-Gly7-Arg8-Glu9-As p10-Val11-Arg12-Asp13-X14-Ser15- Thr16-Asn17-Pro18-Pro19-Arg20-Leu21- X22-Val23-Thr24-Ala25-. Aminopeptidase P cleaved the Arg1-Pro2 bond of bradykinin with a kcat/Km of 5.7 x 10(5) s-1 M-1. N-Terminal fragments of bradykinin including Arg-Pro-Pro, but not Arg-Pro, were also cleaved. The enzyme was shown to have four binding subsites (S1, S1', S2'. S3'), the first three of which must be occupied for hydrolysis to occur. Neuropeptide Y and allatostatin I were hydrolyzed at the Tyr1-Pro2 bond and Ala1-Pro2 bond, respectively. The pH optimum for Arg-Pro-Pro cleavage was 6.8-7.5 in most buffers. The enzyme was most stable in the range of pH 7.0-10.5 in the presence of poly(ethylene glycol). NaCl inhibited activity completely at 2 M. Mn2+ had variable effects on activity, depending on its concentration and the substrate used. Various peptides having an N-terminal Pro-Pro sequence were inhibitory. The enzyme was also inhibited by EDTA, o-phenanthroline, 2-mercaptoethanol, dithiothreitol, p-(chloromercuri)benzenesulfonic acid, apstatin, and captopril. The carboxyalkyl angiotensin-converting enzyme inhibitors, ramiprilat and enalaprilat, inhibited activity in the micromolar range only in the presence of Mn2+.

Dienelactone hydrolase from Pseudomonas cepacia

Dienelactone hydrolases have previously been shown to play a crucial role in chlorocatechol degradation via the modified ortho cleavage pathway. Recently, the enzymes induced in 4-fluorobenzoate-utilizing bacteria have been classified into three groups on the basis of their specificity towards cis- and trans-dienelactone. The dienelactone hydrolase and the 3-oxoadipate enol-lactone hydrolase from Pseudomonas cepacia have now been purified to apparent homogeneity and characterized with respect to molecular mass and amino acid composition. The dienelactone hydrolase has a distinct preference for cis-dienelactone and did not convert the trans isomer or muconolactone, 3-oxoadipate enol-lactone, or 4-fluoromuconolactone to a significant extent. In properties like amino acid composition, pH optimum of activity, and lack of inhibition by p-chloromercuribenzoate, the P. cepacia dienelactone hydrolase differed substantially from 3-oxoadipate enol-lactone hydrolases and other dienelactone hydrolases.

Purification and characterization of protein H, the major porin of Pasteurella multocida

Protein H (B. Lugtenberg, R. van Boxtel, D. Evenberg, M. de Jong, P. Storm, and J. Frik, Infect. Immun. 52:175-182, 1986) is the major polypeptide of the outer membrane of Pasteurella multocida, a bacterium pathogenic for humans and animals. We have purified this protein to homogeneity by size exclusion chromatography after selective extraction with surfactants and demonstrated its pore-forming ability after reincorporation into planar lipid bilayers. In these experiments, the current through the pores was a linear function of the applied voltage in the range of -50 to +50 mV. Voltages beyond +/- 50 mV tended to partially close the channels, giving rise to apparent negative resistances. These observations suggest that protein H channels are probably not voltage regulated in vivo. With the patch clamp technique, single-channel conductance fluctuations of 0.33 nS were recorded in 1 M KCl. Electrophoretic and circular dichroism analyses showed that protein H forms homotrimers stable in sodium dodecyl sulfate at room temperature, with a high content of beta-sheet secondary structure. Upon boiling, the trimers were fully dissociated into monomers with an increase of alpha helix and irregular structure, at the expense of beta sheets. The apparent molecular mass of fully denatured monomers ranged between 37 and 41.8 kDa, depending on the electrophoretic system used for analysis. The trimeric arrangement of protein H was confirmed by image analysis of negatively stained, two-dimensional crystal arrays. This morphological study revealed, in agreement with electrophoretical data, a trimeric structure with an overall diameter of 7.7 nm. Each monomer appeared to contain a pore with an average diameter of 1 nm. Quantitative comparisons revealed that the amino acid composition (hydropathy index of -0.40) and the N-terminal sequence (determined over 36 residues) of protein H are similar to those of bacterial general porins, notably porin P2 of Haemophilus influenzae. We conclude from this set of structural and functional data that protein H of P. multocida is a pore-forming protein related to the superfamily of the nonspecific bacterial porins.

The direct hydrolysis of proteins containing tryptophan on polyvinylidene difluoride membranes by mercaptoethanesulfonic acid in the vapor phase

A procedure for the amino acid analysis of polypeptides that contain tryptophan on polyvinylidene difluoride membranes is described. Lysozyme, carbonic anhydrase, phytochrome, and ovalbumin were tested. The protein, which was separated from others by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, was blotted from the gel onto a polyvinylidene difluoride membrane and directly hydrolyzed by 3 N mercaptoethanesulfonic acid vapor in a vacuum at 176 degrees C for 25 min. The hydrolysate was extracted with 0.1 N HCl and 30% methanol and used for amino acid analysis. The tested proteins were adequately hydrolyzed, and the recovery of tryptophan was very efficient.

Rapid purification and N-terminal sequencing of a potato tuber cyclic nucleotide binding phosphatase

A high affinity cyclic nucleotide binding phosphatase was purified to homogeneity from potato tubers by a rapid procedure involving batchwise elution from carboxymethylcellulose and gel filtration. The phosphatase has a molecular weight of 28,000 as estimated from both SDS-PAGE and gel filtration. The phosphatase binds to Con A-agarose and is eluted by 0.5 M alpha-methylglucoside. The phosphatase catalyses the hydrolysis of nucleoside monophosphates, p-nitrophenylphosphate and O-phospho-L-tyrosine, but not of O-phospho-L-serine or O-phospho-L-threonine. N-terminal sequencing of the phosphatase has revealed significant homology with two similar-size soybean leaf and stem storage glycoproteins.

Alanyl-tRNA synthetase from Escherichia coli, Bombyx mori and Ratus ratus. Existence of common structural features

Alanyl-tRNA synthetase from Escherichia coli, Bombyx mori and rat were examined with respect to the following functional and structural properties: the effect of substrates on sensitivity to proteolysis, secondary structure as determined by circular dichroism, amino acid composition and, in the case of the rat and insect enzymes, partial amino acid sequence determination on a 60-kDa C-terminal tryptic fragment. Digestion of the enzyme from all three sources with trypsin resulted in significant decline in aminoacyl-tRNA synthetase activity with little effect on pyrophosphate-exchange activity. In each case the presence of alanine and ATP together, but not separately, reduced the rate of digestion by trypsin; the largest effect was observed with the enzyme from rat liver. Trypsin digestion generated fragments of 47 kDa and 40 kDa with all three enzymes, but detection of significant quantities of the 47-kDa fragment from the rat enzyme required the presence of ATP and alanine. Trypsin digestion produced a fragment of 60 kDa with all three enzymes, but detection of significant quantities of this fragment with the bacterial enzyme required the presence of ATP and alanine. Limited sequence analysis of the 60-kDa fragment from the insect and rat enzymes indicated that trypsin cleaved both proteins at the same site to generate this species. Similar effects of substrates were observed when the enzymes were digested with chymotrypsin suggesting that the effects of substrates on protease sensitivity were not unique to trypsin. Circular dichroism spectra obtained for the three enzymes were qualitatively and quantitatively similar. There is some similarity in amino acid composition between the rat and insect enzymes.

Molecular cloning, sequence, and tissue distribution of the human ubiquitin-activating enzyme E1

The ubiquitin-activating enzyme E1 catalyzes the first step in ubiquitin conjugation. We have cloned and sequenced the cDNA for human E1. This clone predicts a protein of 110,450 Da. Cys-194 lies within a region of identity to active-site Cys-88 of the ubiquitin carrier protein E2, suggesting a potential role for this region in enzymatic function of this protein. In addition, Cys-454 lies within a region of identity to the thiol ester consensus sequence of several proteins involved in thioester formation. Tissue distribution reveals a single 3.5-kilobase E1 message ubiquitous among tissues and cell lines.

Sequence homology between purple acid phosphatases and phosphoprotein phosphatases. Are phosphoprotein phosphatases metalloproteins containing oxide-bridged dinuclear metal centers?

The amino acid sequences of mammalian purple acid phosphatases and phosphoprotein phosphatases are shown to possess regions of significant homology. The conserved residues contain a high percentage of possible metal-binding residues. The phosphoprotein phosphatases 1, 2A and 2B are proposed to be iron-zinc metalloenzymes with active sites isostructural (or nearly so) with those of the purple phosphatases.

A lectin gene encodes the alpha-amylase inhibitor of the common bean

An alpha-amylase inhibitor that inhibits insect and mammalian alpha-amylases but not plant alpha-amylases, is present in seeds of the common bean (Phaseolus vulgaris). We have purified the alpha-amylase inhibitor by using a selective heat treatment in acidic medium and affinity chromatography with porcine pancreas alpha-amylase coupled to agarose. Under sodium dodecyl sulfate gel electrophoresis, the purified inhibitor gave rise to five bands with mobilities corresponding to molecular masses ranging from 14 to 19 kDa. N-terminal sequencing (up to 15 amino acids) of the polypeptides obtained from these bands resulted in only two different sequences matching two stretches of the amino acid sequence deduced from an already described lectin gene [Hoffman, L. M. (1984) J. Mol. Appl. Gen. 2,447-453]. This gene is different from but closely related to the genes that code for phytohemagglutinin, the major lectin of bean. Further evidence based on amino acid composition, identification of a precursor, and recognition of the product of the gene (expressed in Escherichia coli) by an anti-alpha-amylase inhibitor serum confirms that the inhibitor is encoded by this or a closely related lectin gene. This finding assigns a biological function, which has been described at the molecular level, to a plant lectin gene product and supports the defense role postulated for seed lectins. The lack of homology with other families of enzyme inhibitors suggests that this may be the first member of a new family of plant enzyme inhibitors.

Identification of the long ubiquitin extension as ribosomal protein S27a

Two proteins of unknown function are encoded by 3' in-frame extensions of ubiquitin genes. The polypeptides are synthesized as an additional 52 or 76-80 amino acids on the C terminus of ubiquitin, an unusual arrangement conserved in man, yeast and plants (J. Callis and R. Vierstra, personal communication). Although not homologous to each other or to ubiquitin, both extension proteins are highly basic and contain patterns of cysteine and histidine similar to those proposed to form 'zinc fingers'. The longer C-terminal extension protein (CEP80) is 30% lysine and arginine and, when denatured, behaves like a small cationic protein. Its properties after isolation in physiological conditions, however, suggested that CEP80 is part of an RNA-protein complex. Using the antibodies that confirmed the presence of CEP80 in eukaryotic cells, we show here that the protein is located on ribosomes. Immunoblotting of rat 40S subunit proteins specifically identifies CEP80 as ribosomal protein S27a.

The alignment of protein structures in three dimensions

This article extends the use of dynamic programming algorithms in molecular sequence comparison to the alignment of the alpha-carbon (C alpha-) coordinates of two protein structures in three dimensions. The algorithm is described in detail and is applied to the comparison of alpha-lactalbumin with both hen egg white lysozyme and T4 lysozyme. In the first case, the structures are similar, while the second comparison is between two distantly related molecules. References are made to the usual sequence alignments. A variety of complementary methods are introduced to display the results.

Identification of human lung mast cell kininogenase as tryptase and relevance of tryptase kininogenase activity

We have described previously the IgE-mediated release of kininogenase activity from purified human lung mast cells. Using supernatant fractions from mast cells stimulated with anti-IgE in the presence of deuterium oxide, we have purified this kininogenase to homogeneity by gel filtration and heparin-agarose chromatography and have demonstrated that it is identical to tryptase, the major neutral protease of human lung mast cells. Thus, tryptase and kininogenase activities co-chromatographed through both purification steps with equivalent yields. The final purified kininogenase was free of detectable chymotryptic and carboxypeptidase activities and was identified as tryptase on the basis of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), amino acid composition and inhibition profile. Three such preparations of tryptase were all capable of releasing kinin from each of two different preparations of purified, single-chain, human low molecular weight kininogen. Interestingly, kinin generation was optimal at pH 5.5 and was enhanced by heparin, which has been reported to stabilize tryptase. SDS-PAGE analysis of kininogen hydrolysis by tryptase revealed the formation of a diffusely stained region in the molecular weight range of 60,000-65,000, rather than a discrete heavy chain band. Under optimal conditions, the three tryptase preparations released 10-12 micrograms kinin/hr/mg but released only 2 micrograms kinin/hr/mg at pH 7.2. HPLC analysis revealed that the kinin released was bradykinin. We conclude that the kininogenase activity from human lung mast cells is attributable to tryptase. The unique pH optimum of this reaction of a serine protease, however, raises doubts as to the physiologic significance of this activity.

The identification of large peptide fragments produced from proteins of known sequence: a computerized approach using amino acid composition indexes and its application to thermolysin

An approach to identify fragments produced from proteins of known sequence, based on their amino acid composition, is described. A BASIC computer program (SEARCH) was used to quantitate the degree of relatedness between an experimentally determined amino acid composition and theoretical test peptide compositions calculated from a protein of known amino acid sequence. This computerized approach provides a rapid and objective identification of autolytic peptide fragments produced from thermolysin. Three different types composition indexes were compared with respect to their value versus the number of sequence differences between experimental and test compositions. The difference index was found to show a linear relationship and the lowest level of variability in this regard. On the basis of this comparison, we conclude that the difference index is the most reliable indicator of peptide fragment identity.

Independent folding of autolytic fragments of thermolysin and their domain-like properties

High molecular weight autolysis products from thermolysin have been isolated and identified. The primary fragments correspond to residues 1 to 187-204 (21kD) and residues 187-204 to 316 (12kD), respectively. The fragments are both capable of independent refolding upon removal of denaturant. On the basis of these results, we suggest that the first step in the unfolding pathway of thermolysin involves unfolding of an interdomain region and domain separation. Bound calcium ions at sites 1, 2 and 4 play a major role in protecting the protein against both autolysis and unfolding, probably by stabilizing the interdomain region and enhancing domain-domain interactions.

Genes encoding α-amylase inhibitors are located in the short arms of chromosomes 3B, 3D and 6D of wheat (Triticum aestivum L.)

Three α-amylase inhibitors, designated Inh. I, II and III have been purified from the 70% ethanol extract of hexaploid wheat (Triticum aestivum L.) and characterized by amino acid analysis, N-terminal amino acid sequencing and enzyme inhibition tests. Inhibitors I and III have identical N-terminal sequences and inhibitory properties to those of the previously described 0.19/0.53 group of dimeric inhibitors. Inhibitor II has an N-terminal sequence which is identical to that of the previously described 0.28 monomeric inhibitor, but differs from it in that in addition to being active against α-amylase from Tenebrio molitor, it is also active against mammalian salivary and pancreatic α-amylases. Compensating nulli-tetrasomic and ditelosomic lines of wheat cv. 'Chinese Spring' have been analysed by two-dimensional electrophoresis, under conditions in which there is no overlap of the inhibitors with other proteins, and the chromosomal locations of the genes encoding these inhibitors have been established: genes for Inh. I and Inh. III are in the short arms of chromosomes 3B and 3D, respectively, and that for Inh. II in the short arm of chromosome 6D.

Hexokinase A from mammalian brain: comparative peptide mapping and immunological studies with monoclonal antibodies

Immunological reactivity of partially purified hexokinase A (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) from brain of several vertebrate species has been compared by using enzyme-linked immunosorbent assay and seven monoclonal antibodies raised against the rat brain enzyme. The epitopes recognized by three of these antibodies have been rather widely conserved among the species examined (rat, mouse, guinea pig, rabbit, cat, dog, sheep, cow, pig, chicken), while this was not the case for the epitopes recognized by the other antibodies, which differed markedly in their distribution among these species. The domain structure of these enzymes has been examined by peptide mapping (after limited tryptic digestion) in conjunction with immunoblotting techniques employing monoclonal antibodies. The results indicate that the overall domain structure of these enzymes is similar to that previously described for rat brain hexokinase A, but that there are significant differences in the size of these domains in enzymes from different species.

Isolation and characterization of multiple forms of rat liver UDP-glucuronate glucuronosyltransferase

UDP-glucuronosyltransferase (EC 2.4.1.17) activity was solubilized from male Wistar rat liver microsomal fraction in Emulgen 911, and six fractions with the transferase activity were separated by chromatofocusing on PBE 94 (pH 9.4 to 6.0). Fraction I was further separated into Isoforms Ia, Ib and Ic by affinity chromatography on UDP-hexanolamine-Sepharose 4B. UDP-glucuronosyltransferase in Fraction III was further purified by rechromatofocusing (pH 8.7 to 7.5). UDP-glucuronosyltransferases in Fractions IV and V were purified by UDP-hexanolamine-Sepharose chromatography. The transferase isoforms in Fractions II, III, IV and V were finally purified by h.p.l.c. on a TSK G 3000 SW column. Purified UDP-glucuronosyltransferase Isoforms Ia (Mr 51,000), Ib (Mr 52,000), Ic (Mr 56,000), II (Mr 52,000), IV (Mr 53,000) and V (Mr 53,000) revealed single Coomassie Blue-stained bands on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Isoform III enzyme showed two bands of Mr 52,000 and 53,000. Comparison of the amino acid compositions by the method of Cornish-Bowden [(1980) Anal. Biochem. 105, 233-238] suggested that all UDP-glucuronosyltransferase isoforms are structurally related. Reverse-phase h.p.l.c. of tryptic peptides of individual isoforms revealed distinct 'maps', indicating differences in primary protein structure. The two bands of Isoform III revealed distinct electrophoretic peptide maps after limited enzymic proteolysis. After reconstitution with phosphatidylcholine liposomes, the purified isoforms exhibited distinct but overlapping substrate specificities. Isoform V was specific for bilirubin glucuronidation, which was not inhibited by other aglycone substrates. Each isoform, except Ia, was identified as a glycoprotein by periodic acid/Schiff staining.

Physicochemical properties of proteinases from selected psychrotrophic bacteria

The physicochemical properties of eight extracellular proteinases secreted by psychrotrophic bacteria of dairy origin have been studied. Seven of these proteinases were able to withstand ultra heat treatment (UHT) with D values at 140 degrees C ranging from 2 to 300 s. The six Pseudomonas fluorescens proteinases were glycoproteins of mol. wt 47000-49500. The two Serratia marcescens proteinases, of mol. wt of 51000, did not contain carbohydrate but in other respects were similar to the Pseudomonas proteinases. The proteinases were inhibited by various metal chelators and all contained Ca and Zn in similar proportions. Their amino acid compositions were similar, with alanine as the N-terminal group, cysteine completely absent and very low levels of methionine. Isoelectric points ranged from 5.10 to 8.25. Their physical and chemical properties enabled them to be classified as alkaline metalloendopeptidases. A similarity index (S delta n) was used to predict sequence homology between ten proteinases of known amino acid composition. Comparisons of S delta n of these proteinases showed only minor sequence differences except for those of Ps. fluorescens MC60. Heat resistance could not be related wholly to similarities in protein sequence, but could be related both to the strength of stabilizing Ca2+-protein interactions and to the randomness inherent within the folding of the peptide chain.

New alpha-amylase and trypsin inhibitors among the CM-proteins of barley (Hordeum vulgare)

Barley CM-proteins are a group of at least five salt-soluble components (CMa-e) that can be selectively extracted from endosperm with chloroform/methanol mixtures. N-terminal sequences of proteins CMa, CMb and CMc have been determined and found to be homologous to those previously determined for CMd and CMe, an observation which confirms that their structural genes are members of a dispersed multi-gene family. The purified CM-proteins were tested against trypsin and against alpha-amylases from saliva, pancreas, Aspergillus oryzae, Tenebrio molitor and barley. Besides CMe, which was known to be a trypsin inhibitor, CMc also showed antitrypsin activity, whereas CMa was specifically active against the alpha-amylase from T. molitor and no inhibitory activity was found for proteins CMb and CMd. The evolutionary implications of these findings are discussed.

Neoplastic human fibroblast proteins are related to epidermal growth factor precursor

We report the amino acid composition of two polypeptides, p788 and p789. These polypeptides are reliable markers for neoplastic transformation in human fibroblasts. Their compositions are unusually rich in cysteine and serine. Because the recently reported amino acid sequence of mouse epidermal growth factor precursor (prepro-EGF) is also rich in those two amino acids and because the role of p788 and p789 as markers for neoplastic transformation is consistent with the fact that epidermal growth factor has been shown to play some role in transformation, we investigated the hypothesis that p788 and p789 are related to prepro-EGF. We compared the amino acid composition of p788 with that of all possible interior domains of prepro-EGF of appropriate length. We found that the composition of p788 is remarkably similar to that of residues 630-880 of prepro-EGF. The similarity is sufficiently strong to support the conclusion that it reflects amino acid sequence homology.

Structural differences between two lectins from Cytisus scoparius, both specific for D-galactose and N-acetyl-D-galactosamine

Three lectin fractions were obtained from seeds of the leguminous plant Cytisus scoparius (Scotch broom) by means of affinity chromatography on a N-acetyl-D-galactosamine medium. The first fraction, termed CSIa, was equally well inhibited in haemagglutination experiments by D-galactose and by N-acetyl-D-galactosamine and consisted of a group of isolectins formed from closely related polypeptide chains of approx. Mr 30000. The second fraction, CSIb, was closely related to CSIa in specificity, c.d. and other properties. The third fraction contained a homogeneous lectin, CSII, formed from subunits again of approx. Mr 30000. CSII was 100 times more readily inhibited by N-acetyl-D-galactosamine than by D-galactose. Despite the similarity in specificity, comparative studies of their amino acid composition, c.d. and N-terminal amino acid sequence showed that the CSIa and CSII lectins diverged considerably in structure. The lectin from Cytisus sessilifolius, specific for chitobiose, was also examined and resembled CSIa in composition and c.d. properties.

Comparison of the amino acid compositions and antigenic properties of spiralins purified from the plasma membranes of different spiroplasmas

Spiralins were purified by agarose-suspension electrophoresis after extraction with detergents from the membranes of the following spiroplasmas: Spiroplasma citri C189, S. citri Maroc (R8A2), S. citri Scaph and the honey-bee spiroplasma B88. The four proteins (molecular mass congruent to 26,000 daltons, as determined by sodium dodecyl sulphate-pore gradient electrophoresis) showed very similar amino acid compositions characterized by the absence of methionine and tryptophan and a high polarity index (greater than 49%). When compared with the amino acid composition of S. citri membrane, the four spiralins had little or no histidine, a low content of glycine, leucine, tyrosine, phenylalanine and arginine, and a high content of threonine, alanine and valine. Comparison of the amino acid compositions according to the criteria described by Cornish-Bowden (Anal. Biochem., 1980, 105, 233-238) strongly suggests that all four spiralins are related. A crossed immunoelectrophoretical comparison, however, shows that though the three proteins purified from S. citri strains (serogroup I-1) are antigenically similar, they do not seem to share common epitopes with spiralin from the honey-bee spiroplasma B88 (serogroup I-2).

Isolation of immunochemically distinct form of cytochrome P-450 from microsomes of tulip bulbs

A highly purified cytochrome P-450 was obtained from the microsomes of tulip bulbs (Tulipa gesneriana L.). The molecular weight (Mr = 52,500) and amino acid composition of this plant cytochrome P-450 are similar to those reported for rat livers. On the contrary, Ouchterlony double diffusion analyses indicated that cytochrome P-450 isolated from tulip bulbs shares no common antigenic determinants with those of 9 other plants, in spite of the presence of comparable contents of cytochrome P-450 and/or trans-cinnamate 4-monooxygenase with tulip bulbs.

Molecular analysis of a mutation conferring the high-lysine phenotype on the grain of barley (Hordeum vulgare)

We have analyzed the molecular nature of the Riso 56 mutation that occurs in barley. This mutation results in a depression of hordein accumulation in the grain and consequently in a higher overall lysine content. In particular, the amount of B hordein, which is encoded by the complex locus Hor-2, is decreased by about 75% because of the absence of the major components. The synthesis of certain minor polypeptides, with properties similar to the major B hordeins, remains unaffected. Analysis of endosperm RNA, by in vitro translation and hybridization to various cloned cDNAs derived from hordein mRNA, shows that mRNA for the major B hordeins is not present in the endosperm. Hybridization of a B hordein cDNA clone to gel-fractionated restriction digests of mutant and wild-type DNA indicates that at least 85 kb of DNA has been deleted from the Hor-2 locus in the high-lysine mutant.

The amino acid compositions of proteins are correlated with their molecular sizes

Natural peptides and small proteins in general have amino acid compositions that diverge much more from the average composition of all proteins than do those of proteins. The effect is large and consistent enough to provide a rough check on the measured molecular mass of a protein and to indicate whether it is likely to have a significantly repetitive structure. For example, the alpha-chain of tropomyosin, a highly repetitive protein, has no amino acid composition that would be characteristic of a much smaller protein. The observation provides support for the suggestion [Taylor, Britton & van Heyningen (1983) Biochem. J. 209, 897-899] that tetanus toxin resembles a trimer of the light chain produced by proteolysis.

Structural properties of homogeneous protein disulphide-isomerase from bovine liver purified by a rapid high-yielding procedure

Protein disulphide-isomerase from bovine liver was purified to homogeneity as judged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, two-dimensional electrophoresis and N-terminal amino acid analysis. The preparative procedure, a modification of that of Carmichael, Morin & Dixon [(1977) J. Biol. Chem. 252, 7163-7167], is much faster and higher-yielding than previous procedures, and the final purified material is of higher specific activity. The enzyme has Mr 57 000 as determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, both in the presence and in the absence of thiol compounds. Gel-filtration studies on Sephadex G-200 indicate an Mr of 107 000, suggesting that the native enzyme is a homodimer with no interchain disulphide bonds. Ultracentrifugation studies give a sedimentation coefficient of 3.5S, implying that the enzyme sediments as the monomer. The isoelectric point, in the presence of 8 M-urea, is 4.2, and some microheterogeneity is detectable. The amino acid composition is comparable with previous analyses of this enzyme from bovine liver and of other preparations of thiol:protein disulphide oxidoreductases whose relation to protein disulphide-isomerase has been controversial. The enzyme contains a very high proportion of Glx + Asx residues (27%). The N-terminal residue is His. The pure enzyme has a very small carbohydrate content, determined as 0.5-1.0% by the phenol/H2SO4 assay. Unless specific steps are taken to remove it, the purified enzyme contains a small amount (5 mol/mol of enzyme) of Triton X-100 carried through the purification.

Evolutionary divergence of chloroplast and cytosolic glyceraldehyde-3-phosphate dehydrogenases from angiosperms

Extracts from 13 different angiosperm species (spinach, mustard, pea, bean, tomato, cucumber, pumpkin, maize, sorghum, rye, wheat, oats, barley) were submitted to electrophoresis under nondenaturing conditions and stained for enzyme activities of cytosolic and chloroplast glyceraldehyde-3-phosphate dehydrogenases by a modified tetrazolium test of high sensitivity. Zymograms of the cytosolic enzyme revealed a single band of similar electrophoretic mobility for all but one species, the tomato, which displayed an ordered set of five different bands. In contrast, zymograms of the chloroplast dehydrogenase are highly different, containing between two and five distinct bands of variable electrophoretic mobilities according to the plant species examined. This variability of the native chloroplast enzyme is paralleled by a remarkable interspecific heterogeneity of the enzyme with respect to subunit size and number, as shown by dodecylsulfate electrophoresis of the purified chloroplast enzyme from 11 different angiosperm species. The present data suggest that cytosolic and chloroplast glyceraldehyde-3-phosphate dehydrogenases belong to two separate protein families of different evolutionary rate. While the cytosolic enzyme is probably an extremely conservative protein like the corresponding enzymes from animals, yeast and bacteria, the chloroplast enzyme seems to change rather rapidly during evolution.

Relatedness of acyl carrier proteins shown by amino acid compositions

1. Relatedness among the following carrier proteins was assessed on the basis of amino acid compositions: eight acyl carrier proteins (ACP's) associated with fatty acid synthesis, ACP's associated with citrate lyase and citramalate lyase, a biotin carboxyl carrier protein and cytochrome 552. Two independent indices of amino acid composition were used. 2. The fatty acid synthesis-associated ACP's of many organisms and the lyase-associated ACP's show a high degree of relatedness among one another. 3. The ACP's show no relatedness to biotin carboxyl carrier protein or cytochrome 552.

The comparative isozymology of vertebrate hexokinases

1. Multiple hexokinase isozymes have been found in most vertebrates. Since each isozyme displays distinctive structural, kinetic and regulatory characteristics, the system qualifies as a useful probe for studies on molecular evolution. 2. At least seven types of chromatographic patterns of liver hexokinases have been observed in mammals. In contrast, each Class of lower vertebrates present only two or three distinct profiles. 3. Aves and higher Reptiles do not have the same hexokinase isozymes as other vertebrates. The nature of the differences is poorly understood. 4. Ontogenetic changes of liver hexokinase profiles are quite different in rat, chick and frog. 5. Structural comparisons of three vertebrate hexokinases having a molecular weight of approximately 100,000 suggest that those isozymes originated from a pre-vertebrate ancestor through gene duplication followed by fusion and further duplication events. Another hexokinase (the so-called glucokinase), with half the molecular weight, may have arisen either as the result of subsequent even splitting of the fused gene or, less probably, by divergence from a duplicated gene before the fusion event.