Peptides and micro-organisms

Characterization and function analysis of a Kazal-type serine proteinase inhibitor in the red claw crayfish Cherax quadricarinatus

Kazal-type serine proteinase inhibitors (KPIs) function in physiological and immunological processes requiring proteinase action. In the present study, the first Cherax quadricarinatus KPI gene (designated CqKPI) was identified and characterized. The open reading frame of CqKPI contains 405 nucleotides and encodes a protein of 134 amino acids. CqKPI has two Kazal domains comprising 44 amino acid residues with the conserved amino acid sequence C-X₃-C-X₇-C-X₆-Y-X₃-C-X₆-C-X₁₂-C. Each Kazal domain has six conserved cysteine residues, which can form a structural conformation of three pairs of disulfide bonds stabilizing the Kazal domain. CqKPI exhibited high similarity with previously identified KPIs from crayfish hemocytes. The results of tissue distribution showed that CqKPI had the highest expression level in hemocytes, and this was in agreement with phylogenic relationships. Recombinant CqKPI (rCqKPI) was heterologously expressed in Escherichia coli and purified for further study. The proteinase inhibition assays suggested that rCqKPI could potently inhibit elastase and weakly inhibit trypsin, subtilisin A, and proteinase K, but not α-chymotrypsin. It can firmly bind to Bacillus hwajinpoensis, Staphylococcus aureus, and Vibrio parahaemolyticus, with weak binding to Candida albicans. In addition, CqKPI inhibited bacterial secretory proteinase activity and inhibited the growth of B. hwajinpoensis and C. albicans. These data suggest that CqKPI might be involved in anti-bacterial immunity, acting as an inhibitor of the proteinase cascade in the resistance to invasion of pathogens.

Amino acids other than glutamate affect the expression of the GAD system in Listeria monocytogenes enhancing acid resistance

The Glutamate Decarboxylase (GAD) system is important for survival of L. monocytogenes and other microorganisms under acidic conditions. Environmental conditions influence the function of the GAD system. Until now, the only conditions known to lead to increased transcription of the GAD system are the stationary phase in rich media and anoxic conditions. Previously, we showed that transcription of the GAD system requires unidentified compounds other than glutamate present in rich media. Following a test looking at various compounds we identified for first time that peptone, tryptone and casamino acids activate the GAD system under oxic conditions suggesting that amino acid(s) other than glutamate and/or peptides are important for the above process. The defined medium, where the GAD system is inactive, once it is supplemented with the above compounds results in an active intracellular and extracellular GAD system and increased acid resistance. Through functional genomics we show that these compounds are required for GadD2 activity and although we previously showed that GadD3 is active part of the intracellular GAD system, the supplementation did not activate this gene. The above is explained by the fact that only gadD2 transcription was upregulated by these compounds while the transcription of gadD1 and gadD3 remained unaffected. Together our results show that the L. monocytogenes GadD2 decarboxylase is activated in the presence of amino acids or peptides other than glutamate, a finding that has important implications for acid tolerance and food safety.

Soluble microbial products (SMPs) release in activated sludge systems: a review

This review discusses the characterization, production and implications of soluble microbial products (SMPs) in biological wastewater treatment. The precise definition of SMPs is open to talk about, but is currently regarded as “the pool of organic compounds that are released into solution from substrate metabolism and biomass decay”'. Some of the SMPs have been identified as humic acids, polysaccharides, proteins, amino acids, antibiotics, extracellular enzymes and structural components of cells and products of energy metabolism. They adversely affect the kinetic activity, flocculating and settling properties of sludge. This review outlines some important findings with regard to biodegradability and treatability of SMPs and also the effect of process parameters on their production. As SMPs are produced during biological treatment process, their trace amounts normally remain in the effluent that defines the highest COD removal efficiency. Their presence in effluent represents a high potential risk of toxic by-product formation during chlorine disinfection. Studies have indicated that among all wastewater post-treatment processes, the adsorption by granular activated carbon combined with biologically induced degradation is the most effective method for removal of SMPs. However, it may be concludes that the knowledge regarding SMPs is still under progress and more work is required to fully understand their contribution to the treatment process.

Consequences of packaging on bacterial growth. Meat is an ecological niche

Meat is a good support for bacterial growth and particularly for bacteria which are specific of meat and meat products. Little is known about the physiological and biochemical factors which could explain why some bacterial species are only isolated from meat. This review tentatively points out, from an ecological point of view, some of these factors in Gram negative and Gram positive micro-organisms influencing storage life.

Regulation of Proteolytic Activity in the Hyperthermophile Pyrococcus furiosus

Pyrococcus furiosus was shown to grow on casein or peptides as the sole carbon, energy, and nitrogen sources, while maltose could be used as a carbon and energy source only if peptides were present in the medium. A mixture of all 20 single amino acids could not replace the peptide requirement. Specific intracellular proteolytic activity was induced under low casein or tryptone levels and was decreased by the addition of maltose to both peptide-limiting and peptide-rich media in batch and continuous cultures. In a peptide-limited chemostat, activity towards azocasein and MeO-Suc-Arg-Pro-Tyr-p-nitroanilide reached a maximum at a dilution rate of 0.28 h, while activity toward l-lysine-p-nitroanilide reached a maximum at 0.50 h. Under peptide-limiting conditions, levels of the 66-kDa protease (S66) were enhanced relative to those of other cell proteins. Preliminary evidence suggests that this protease is immunologically related to the eukaryotic multicatalytic proteinase complex (proteosome).

Characterization, kinetics, and possible function of Kazal-type proteinase inhibitors of Chinese white shrimp, Fenneropenaeus chinensis

Serine proteinase inhibitor plays an essential role in arthropods by restraining the activities of endogenic or exogenic serine proteinases. Four Kazal-type serine proteinase inhibitors, Fcspi-1-4, from the hepatopancreas of Chinese white shrimp, Fenneropenaeus chinensis, were cloned and identified. The open reading frames (ORFs) of Fcspis are 1389, 1236, 1080, and 939 base pairs, encode the pre-proteins of 462, 411, 359, and 312 amino acids and form the 9, 8, 7, and 6 typical Kazal domains, respectively. When analyzing the amino acid sequences of the four inhibitors, it was found that they might have been derived from the same transcript, which was subjected to alternative splicing, and none of the Kazal domains were identical within each inhibitor. Multiple alignments showed that the Kazal inhibitors were homologous with a conserved motif of Cx(3)Cx(6)VCGSDGxTYx(3)CxLx(5)Cx(5)ITx(6)GC. The results from RT-PCR indicated that the expression of Fcspis as a whole was upregulated by bacterial challenge, no obvious change was noticed after viral challenge, and Fcspi-1 had a similar expression pattern with that of Fcspis. Recombinant FcSPIs were successfully expressed in bacteria and purified for further study. Recombinant FcSPI-1 was sensitive to DTT and had thermal stability. The inhibitory kinetics assay suggested that rFcSPI-1 was a mixed-type fast tight binding inhibitor with inhibitory activities against subtilisin A at a molar ratio of 1:1, 1:2 against proteinase K, and 2:1 against elastase. It can firmly bound to two Gram-positive and one Gram-negative bacteria but without anti-bacterial ability. In addition, it inhibited the activities of both bacterial-secreted proteinases and natural chymotrypsin of Chinese white shrimp, suggesting that FcSPI-1 may participate in the immune defence response by inhibition of bacterial pathogen proteinases and possibly be involved in the regulation of shrimp proteinase activity.

Transport and hydrolysis of peptides by microorganisms

The structural specificities of the dipeptide and oligopeptide permeases of E. coli are briefly reviewed and related to the requirements found for other microorganisms. New, quick, sensitive methods for studying peptide transport are described, based on the following: (i) peptide-dependent incorporation of free radioactive amino acid into newly synthesized protein by a double amino acid auxotroph, (ii) colorimetric assay of peptide-dependent enzyme synthesis by an amino acid auxotroph, (iii) dansyl fingerprint technique. These approaches provide information on peptide binding affinity to a permease and rates of peptide uptake and amino acid efflux. Among current and future research areas considered are: the influence of the pKb of the N-terminal amino group on transport, generality of peptide transport in microorganisms, energy coupling and regulation, involvement of binding proteins, and the 'smugglin' concept. Peptide hydrolysis, and nutritional ultilization of peptides, by microorganisms are briefly discussed.

Effects of operational factors on soluble microbial products in a carrier anaerobic baffled reactor treating dilute wastewater

The effects of feed strength, hydraulic residence time (HRT), and operational temperatures on soluble microbial product (SMP) production were investigated, to gain insights into the production mechanism. A carrier anaerobic baffled reactor (CABR) treating dilute wastewater was operated under a wide range of operational conditions, namely, feed strengths of 300-600 mg/L, HRTs of 9-18 h, and temperatures of 10-28 degrees C. Generally, SMP production increased with increasing feed strength and decreasing temperature. At high temperature (28 degrees C), SMP production increased with decreasing HRT. As the temperature was decreased to 18 and 10 degrees C, the SMP production was at its peak for 12 h HRT. Therefore, temperature could be an important determinant of SMP production along with HRT. A higher SMP to soluble chemical oxygen demand (SCOD) ratio was found at high temperature and long HRT because of complete volatile fatty acid degradation. SMP accounted for 50%-75% of the SCOD in the last chamber of the CABR. As a secondary metabolite, some SMP could be consumed at lower feed strength.

Characterisation of dissolved combined amino acids in marine waters

Dissolved combined amino acids (DCAA) are important constituents of the dissolved organic nitrogen (DON) pool in marine environments, although little is known about their sources, dynamics and sinks. The DCAA pool consists of various compounds including proteins and peptides, proteins linked to sugars and amino acids adsorbed to humic and fulvic acids, clays and other materials. The proportions of each of these components and the extent to which they are used by microplankton living within the photic zone are not known. An investigation was carried out, using (15)N isotope dilution techniques, to determine the concentration and composition of dissolved amino acid pools in the marine environment. A near-shore seawater sample was collected and split into fractions to determine the concentrations of dissolved free amino acids (DFAA), DCAA and a <3 kDa dissolved peptide fraction (DPEP; obtained by ultrafiltration). DCAA and DPEP fractions were hydrolysed to yield free amino acids and all samples were analysed by gas chromatography/mass spectrometry (GC/MS) as isobutyloxycarbonyl/tert-butyldimethylsilyl derivatives. The DFAA was the smallest fraction representing approximately 1% of total dissolved amino acids. The majority of DCAA was contained in the low molecular weight DPEP fraction (90%) and was probably as a result of release from phytoplankton and degradation by heterotrophic bacteria.

Bacterial proteinases as targets for the development of second-generation antibiotics

The emergence of bacterial pathogen resistance to common antibiotics strongly supports the necessity to develop alternative mechanisms for combating drug-resistant forms of these infective organisms. Currently, few pharmaceutical companies have attempted to investigate the possibility of interrupting metabolic pathways other than those that are known to be involved in cell wall biosynthesis. In this review, we describe multiple, novel roles for bacterial proteinases during infection using, as a specific example, the enzymes from the organism Porphyromonas gingivalis, a periodontopathogen, which is known to be involved in the development and progression of periodontal disease. In this manner, we are able to justify the concept of developing synthetic inhibitors against members of this class of enzymes as potential second-generation antibiotics. Such compounds could not only prove valuable in retarding the growth and proliferation of bacterial pathogens but also lead to the use of this class of inhibitors against invasion by other infective organisms.

A di- and tripeptide transport system can supply Listeria monocytogenes Scott A with amino acids essential for growth

Listeria monocytogenes takes up di- and tripeptides via a proton motive force-dependent carrier protein. This peptide transport system resembles the recently cloned and sequenced secondary di- and tripeptide transport system of Lactococcus lactis (A. Hagting, E. R. S. Kunji, K. J. Leenhouts, B. Poolman, and W. N. Konings, J. Biol. Chem. 269:11391-11399, 1994). The peptide permease of L. monocytogenes has a broad substrate specificity and allows transport of the nonpeptide substrate 5-aminolevulinic acid, the toxic di- and tripeptide analogs, alanyl-beta-chloroalanine and alanyl-alanyl-beta-chloroalanine, and various di- and tripeptides. No extracellular peptide hydrolysis was detected, indicating that peptides are hydrolyzed after being transported into the cell. Indeed, peptidase activities in response to various synthetic substrates were detected in cell extracts obtained from L. monocytogenes cells grown in brain heart infusion broth or defined medium. The di- and tripeptide permease can supply L. monocytogenes with essential amino acids for growth and might contribute to growth of this pathogen in various foods where peptides are supplied by proteolytic activity of other microorganisms present in these foods. Possible roles of this di- and tripeptide transport system in the osmoregulation and virulence of L. monocytogenes are discussed.

Expression of periplasmic binding proteins for peptide transport is subject to negative regulation by phosphate limitation in Escherichia coli

It is well recognised that phosphate limitation in Escherichia coli causes enhanced synthesis of a variety of proteins involved in maximising the uptake and utilisation of the available phosphate. In contrast to this situation, we report here that these same conditions repress synthesis of the periplasmic binding proteins for both the oligopeptide (Opp) and dipeptide permeases (Dpp), and of certain other periplasmic proteins. Regulation in the former case is mediated by the Pho regulon; genes controlled by this mechanism lack efficient -35 promoter regions, and instead, an activator protein, PhoB, binds to a specific 'Pho box' sequence, ten bases upstream from a -10 promoter, thereby facilitating binding of RNA polymerase and leading to enhanced transcription. In the latter case, putative Pho boxes can be identified in the promoter regions of opp and dpp (and of other binding proteins), but in these genes they overlap the RNA polymerase binding sites of good promoters. We speculate that this different Pho box location may allow PhoB to act as a repressor of transcription of these genes. The promoter region for the sigma factor, sigma 32, (RpoH) also contains a putative Pho box, implying that it may be involved in the enhanced synthesis and secretion of proteins required under phosphate limitation.

Simultaneous exploitation of different peptide permeases by combinations of synthetic peptide smugglins can lead to enhanced antibacterial activity

Various synthetic, peptide prodrugs (smugglins) were tested alone and in combination for activity against Escherichia coli. The smugglins may be transported through any of three peptide permeases, and once inside the bacteria are activated by intracellular peptidase action to release their intrinsically impermeant, antibacterial moieties. When each such antibiotic peptide present in a mixture was accumulated via a different permease, synergistic effects could be observed. Synergy was also found when smugglins were combined with other non-peptide antibiotics. The principle of using smugglin combinations could extend the scope of their application, and should minimise the potential problem that can arise from the occurrence of resistant, transport mutants. The smugglin interactions were studied using a modified microtitre plate assay.

Constituents of salivary supernatant responsible for stimulation of oxygen uptake by the bacteria in human salivary sediment

The 10,000 g supernatant of wax-stimulated whole saliva was fractionated by gel filtration and its components were tested along with amino acids, small peptides and urea for their ability to stimulate this oxygen uptake, and for their effects on pH. Fractions containing the larger components, the proteins and large peptides, stimulated much less oxygen uptake than unfractionated supernatant, and caused a small decrease in pH. Analysis with anthrone indicated that both these effects were due mainly to the carbohydrate associated with these constituents. In contrast, fractions containing the remaining lower molecular-weight components stimulated substantial oxygen uptake and a rise in pH; both effects were like those seen with whole saliva supernatant. The oxygen effects were attributed mainly to certain amino acids and small peptides in the small molecular-weight fractions. Ornithine, arginine, proline and glutamic acid consistently stimulated oxygen uptake by the oral microflora in a test of 23 amino acids with the sediments of 13 subjects. Ornithine and arginine at the same time stimulated a significant rise in pH, whereas the other two amino acids showed no such effect. Variable and sometimes significant oxygen uptake was seen with alanine, aspartic acid, asparagine, glutamine and cysteine in 4-7 of the subjects; infrequent or no effects were seen with the remainder of the amino acids tested. There was some evidence to suggest that amino acid stimulation of oxygen uptake may be inducible. Urea had no effect on uptake but did contribute significantly to the pH rise. Small peptides containing those amino acids that could stimulate oxygen uptake also stimulated such uptake; peptides without such acids did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of a Streptococcus sanguis strain to arginine-containing peptides

For dental plaque organisms such as Streptococcus sanguis, the ecological importance of the ability to utilize arginine as an energy source has been established in previous studies. The present investigation was undertaken to determine the ability of a strain of S. sanguis to process unsubstituted arginine-containing peptides. The organism was grown under glucose-limited conditions in a chemically defined medium, and peptide was added to washed, resting cells in a pH-stat at pH 7.0. Filtrates taken at appropriate time intervals were assayed for peptide, free amino acids, and metabolites. Irrespective of the position of the arginine residue, all peptides tested were attacked, although those that possessed a C-terminal arginine (including a tetrapeptide) were processed at a faster rate than were those in which arginine was N terminal. However, C-terminal arginine was cleaved only slowly from a peptide containing 24 residues. In each case, most of the released arginine was converted to ornithine via the arginine deiminase pathway. Such peptidase activities appeared to occur at or near the cell surface and were probably constitutive. It was found that the organism grew in chemically defined medium containing arginine that was present solely in the form of a tripeptide, and also that a strain of S. mutans possessed only a limited ability to attack arginine-containing peptides and was unable to utilize the released arginine.

The prevention of sub-surface demineralization of bovine enamel and change in plaque composition by casein in an intra-oral model

The ability of bovine milk phosphoprotein (casein) to be incorporated into plaque, prevent enamel sub-surface demineralization, and affect bacterial composition was determined using a modified intra-oral caries model. The intra-oral model consisted of a removable appliance containing a left and right pair of bovine enamel slabs placed to simulate an approximal area. Supragingival plaque was collected and impacted into the left and right inter-enamel spaces. The left side of the appliance was exposed to various sugar and salt solutions, while the right side was exposed to sugar and casein solutions. Sodium caseinate, the major fraction alpha s1-casein, and a tryptic digest of alpha s1-casein (TD-casein) were studied. Sodium caseinate at a level of 2% w/v in a 3% sucrose-3% glucose-salt solution (pH 7.0) prevented sub-surface enamel demineralization over a ten-day period as shown by microradiography and microhardness. Two exposures of a 2% w/v sodium caseinate, alpha s1-casein, or TD-casein solution (pH 7.0) per day prevented sub-surface enamel demineralization caused by six exposures of a 3% sucrose-3% glucose-salt solution per day over a ten-day period. Intact alpha s1-casein and tryptic peptides were shown immunochemically to be incorporated into the inter-enamel plaque. The incorporation of casein and its breakdown in plaque did not produce a significant change in the amount or composition of plaque bacteria. The ability of casein and tryptic peptides to prevent enamel demineralization was related to their incorporation into plaque, thereby increasing plaque calcium phosphate and acid-buffering capacity by the phosphoseryl, histidyl, glutamyl, and aspartyl residues and indirectly through catabolism by plaque bacteria.

Purification and characterization of a novel metalloendopeptidase from Streptococcus cremoris H61. A metalloendopeptidase that recognizes the size of its substrate

An endopeptidase (LEP-II), which has a unique substrate specificity, was purified to homogeneity by conventional chromatographic techniques from Streptococcus cremoris H61. The enzyme was a metalloendopeptidase since it was inhibited by EDTA and 1,10-phenanthroline; the metal-depleted enzyme could be fully reactivated by micromolar levels of Zn2+ and was not inhibited by specific inhibitors for serine or thiol protease. The molecular mass of the enzyme was estimated to be 80 kDa by Sephacryl S-300 gel filtration and high-performance liquid chromatography with a TSK-G3000SW column. The enzyme consisted of two identical subunits and the N-terminal sequence of LEP-II was determined up to the 19th residue. Although the enzyme had a broad substrate specificity it specifically hydrolyzed the peptide bonds involving the amino groups of hydrophobic amino acid residues. Various small polypeptides, such as alpha s1-CN(f1-23), alpha s1-CN(f91-100), oxidized insulin B chain, glucagon and some biologically active peptides were hydrolyzed. However, a variety of larger polypeptides or proteins, such as alpha s1-CN(f1-54), alpha s1-CN(f61-123), alpha s1-CN(f136-196), alpha s1-casein, beta-casein, and kappa-casein were not hydrolyzed. LEP-II recognized the size of its substrates, which were limited below a molecular mass of about 3.5 kDa.

Binding specificity of the periplasmic oligopeptide-binding protein from Escherichia coli

The structural properties required for the binding of peptide substrates to the Escherichia coli periplasmic protein involved in oligopeptide transport were surveyed by measuring the ability of different peptides to compete for binding in an equilibrium dialysis assay with the tripeptide Ala-Phe-[3H]Gly. The protein specifically bound oligopeptides and failed to bind amino acids or dipeptides. Acetylation of the peptide amino terminus of (Ala)3 severely impaired binding, whereas esterification of the carboxyl terminus significantly reduced but did not completely eliminate binding. Peptides composed of L-amino acids competed more effectively than did peptides containing D-residues or glycine. Experiments with a series of alanyl peptide homologs demonstrated a decrease in competitive ability with increasing chain length beyond tripeptide. Competition studies with tripeptide homologs indicated that a wide variety of amino acyl side chains were tolerated by the periplasmic protein, but side-chain composition did affect binding. Fluorescence emission data suggested that this periplasmic protein possesses more than one substrate-binding site capable of distinguishing peptides on the basis of amino acyl side chains.

THE BIOLOGY OF MYCORRHIZA IN THE RICACEAE: IX. PEPTIDES AS NITROGEN SOURCES FOR THE ERICOID ENDOPHYTE AND FOR MYCORRHIZAL AND NON-MYCORRHIZAL PLANTS

The ericoid mycorrhizal endophyte Hymenoscyphus ericae (Read) Korf &Kernan was grown both in pure culture and in mycorrhizal association with the host plant Vaccinium corymbosum L. on media containing peptides of differing chain length as sole nitrogen sources. The ability to utilize the peptide nitrogen was assessed in terms of growth of the fungus and of growth and nitrogen content of the plants. The tripeptide, glutathione, and alanine units of 1-6 amino acid residues in length were all readily utilized by the endophyte, though assimilation was less rapid in the case of the longer chain lengths. Mycorrhizal seedlings showed significantly higher yields and had higher nitrogen contents than non-mycorrhizal seedlings in almost all cases. The physiological and ecological implications of these results are discussed.

THE BIOLOGY OF MYCORRHIZA IN THE ERICACEAE: X. THE UTILIZATION OF PROTEINS AND THE PRODUCTION OF PROTEOLYTIC ENZYMES BY THE MYCORRHIZAL ENDOPHYTE AND BY MYCORRHIZAL PLANTS

The ability of the ericoid mycorrhizal endophyte to utilize a range of proteins as substrates for growth is assessed in liquid culture and in mycorrhizal association with host plants. Some aspects of proteolytic enzyme production are also investigated. The fungus readily utilizes the soluble protein bovine serum albumin (BSA) as sole nitrogen and carbon source, and produces lower yields on less soluble plant and animal proteins. Maximum yields of endophyte on all substrates were obtained in the pH range 3 to 5. Infection provides a significant enhancement of plant growth on agar over this pH range on most of the proteins. Yields and nitrogen contents of mycorrhizal plants grown on cellulose sheets with BSA as sole N source were significantly higher than those of the uninfected controls, which were unable to use protein. Using a chromogenic substrate it was shown that the pH optimum for enzyme activity is comparable with that for utilization of protein in pure culture and in mycorrhizal association. Non-mycorrhizal plants produced negligible proteolytic activity. The significance of these observations is discussed in relation to the nutrition of both host and fungus in the natural environment, and the broader ecological implications of the results are assessed.

Genetic characterization and molecular cloning of the tripeptide permease (tpp) genes of Salmonella typhimurium

Of the three bacterial peptide transport systems only one, the oligopeptide permease, has been characterized in any detail. We have now isolated Salmonella typhimurium mutants deficient in a second transport system, the tripeptide permease (Tpp), using the toxic peptide alafosfalin. Alafosfalin resistance mutations map at three loci, the gene encoding peptidase A (pepA) and two transport-defective loci, tppA and tppB. Locus tppA has been mapped to 74 min on the S. typhimurium chromosome, cotransducible with aroB, and is a positive regulator of tppB. Locus tppB maps at 27 min in the cotransduction gap between purB and pyrF. We cloned tppB, the structural locus for the tripeptide permease. Two simple methods are described for mapping the location of cloned DNA fragments on the chromosome of S. typhimurium.

Dipeptidyl carboxypeptidase-deficient mutants of Salmonella typhimurium

Mutants of Salmonella typhimurium deficient in dipeptidyl carboxypeptidase have been isolated by screening for clones unable to use N-acetyl-L-alanyl-L-alanyl-L-alanine (AcAla3) as the sole nitrogen source. An insertion of the transposable element Tn10 near dcp (the locus coding for dipeptidyl carboxypeptidase) has been isolated and used to map the locus in the interval between purB and trp, an otherwise genetically silent region of the S. typhimurium map. All dcp mutants could still grow using N-acetyl-L-alanyl-L-alanyl-L-alanyl-L-alanine (AcAla4) as the sole nitrogen source. Crude extracts from the dcp mutants failed to hydrolyze AcAla3 but retained approximately 80% of the wild-type activity toward AcAla4. Several lines of evidence indicate that hydrolysis of AcAla4 in the dcp mutant results from the action of a new peptidase distinct from dipeptidyl carboxypeptidase. A mutant strain lacking dipeptidyl carboxypeptidase in addition to peptidases N, A, B, and D showed reduced protein breakdown during carbon starvation compared with a strain lacking only peptidases N, A, B, and D.

The free amino acids in human dental plaque

Analysis of plaques from maxillary and mandibular incisors for free amino acids showed that the dicarboxylic amino acids, glutamic and aspartic, were present in largest amounts, with glutamic acid comprising at least 50 per cent of the total pool. Other amino acids in decreasing order of prominence included proline, ornithine, alanine, lysine, glycine, threonine and serine. This pattern was basically the same in the plaques from the different incisor sites but was clearly different from those of hydrolysates of either the plaque bacteria or the plaque matrix. The results were consistent with the most prominent plaque-free amino acids being associated mainly with the intermediary metabolism of the plaque bacteria. Urea and glucose were then applied to plaque in vivo in the form of rinses to determine if during their metabolism any of the plaque amino acids are affected. Glutamic- and aspartic-acid concentrations both rose after plaque exposure to urea accompanied by a small rise in alanine. After glucose exposure, aspartic- and glutamic-acid concentrations both showed large decreases and alanine showed a small increase. With glucose plus urea, glutamic acid rose and fell, aspartic acid decreased slightly and alanine increased several fold. In each case, the other free amino acids showed little or no change. Thus glutamic and aspartic acids are major components of the intra-cellular pool of amino acids and probably play an important role in alanine synthesis, presumably by facilitating transamination of pyruvate.

Catabolism of arginine by the mixed bacteria in human salivary sediment under conditions of low and high glucose concentration

The catabolism of glucose by the oral mixed bacteria results in a lowering of the pH whereas arginine degradation favours a rise. In the mouth, low and high levels of glucose cause different plaque pH conditions which, in turn, might affect the rate and mode of degradation of arginine. This possibility was examined in the suspended salivary-sediment system where these pH conditions can be simulated. With the pH, the metabolic parameters examined were arginine utilization, ammonia, carbon dioxide and putrescine formation, utilization of glucose and changes in levels of L(+)- and D(-)-lactic acid. At the lower glucose concentration, the pH rapidly fell and then slowly rose whereas, with the higher glucose level, the pH showed a greater fall and no subsequent rise. The more acidic pH conditions favoured by the higher glucose level inhibited arginine degradation and the appearance of its various end-products and intermediates. Arginine degradation with arginine-[U-14C] and paper chromatography-autoradiography showed successive appearance of citrulline, ornithine and putrescine and, depending upon the pH, some succinate. When the pH was held constant at several different values, arginine degradation was optimal when the pH was near neutrality. In supplementary experiments, arginine had little effect on the ability of the oral mixed bacteria to utilize glucose and produce and utilize lactic acid, whereas the arginine peptide, arginylisoleucine and saliva supernatant stimulated these processes. Thus glycolysis enhancement and a more rapid clearance of fermentable carbohydrate by the oral bacteria would accompany pH-rise activity with arginine peptide and saliva but would not accompany pH-rise activity with arginine.

Production of the Kanagawa hemolysin by Vibrio parahaemolyticus in a synthetic medium

A synthetic medium capable of supporting growth of Vibrio parahaemolyticus is described. Growth yields and generation times were comparable to growth in a complex medium, although Kanagawa hemolysin was undetectable in the synthetic medium. Upon the addition of single amino acids to this synthetic medium, only D-tryptophan induced production of the hemolysin. L-Tryptophan was found to inhibit the action of the D-stereoisomer. The response to D-tryptophan was pH dependent; the greatest hemolysin expression occurred at pH values below 6.5. The addition of 100 micrometers D-tryptophan to early-logarithmic-phase cultures caused an inhibition of growth and of substrate utilization, both of which lasted 7 h. During this time, hemolysin was produced only intracellularly. The hemolysin appeared in the supernatant only when growth recommenced. The hemolysins within the cell and in the supernatant were both inactivated by antiserum raised against the standard Kanagawa hemolysin.

Utilization of D-phenylglycyl-glycine in Escherichia coli

Escherichia coli K 12 is able to utilize the dipeptide D-phenylglycyl-glycine as a source of glycine. Growth experiments with a glycine auxotrophic mutant show that utilization of there dipeptide is competitively inhibited by D-alanine at a Ki of 4 x 10(-4) M. In contrast, L-alanyl-L-alanine which is transported via the system specific for dipeptides does not interfere with the utilization of D-phenylglycyl-glycine. This indicates that the dipeptide is hydrolyzed prior to uptake, and D-alanine therefore competes with the uptake of glycine via the transport system common for both amino acids. This was confirmed by examining the growth response of various transport mutants. A mutant deficient in the transport of oligo- and dipeptides grows as well as the wild type on D-phenylglycyl-glycine, whereas the growth of mutants deficient in the transport of glycine is severely impaired or prevented with this dipeptide. It is therefore demonstrated that D-phenylglycyl-glycine is hydrolyzed prior to uptake. This is a mechanism of peptide utilization in E. coli K 12 which is distinct from that described so far for other dipeptides.

Evidence for di-peptide uptake in Tetrahymena

We have established growth conditions in a synthetic nutrient medium in such a way that utilization of free phenylalanine, but not of phenylalanine-containing di-peptides, limits cell multiplication in species of the genus Tetrahymena (Ciliata). These results suggest that these cells take up intact di-peptides.

Peptidase activity in Tetrahymena

This report strongly suggests that two compartments in Tetrahymena thermophila contain peptidase activity: the cytoplasm and the outer cell surface. Determinations of amino acid concentrations in the extracellular medium upon incubation of cells with peptides suggest that the surface-bound peptidase activity hydrolyses di- and tri-phenylalanine equally fast on a molar basis. Growth experiments designed to characterize the in vivo peptidase specificities showed that both T. thermophila and T. pyriformis can use L-leucyl-L-leucine, but not L-leucyl-D-leucine as a leucine donor. These results are independent of whether the cells form food vacuoles or not.

Soluble di- and aminopeptidases in Escherichia K-12. Dispensible enzymes

As part of a study of the peptidase content of Escherichia coli K-12, two peptidase-deficient amino acid auxotrophs isolated and characterized by Miller as pepD- (strain CM17) and pepD- pepN- pepA- pepB- pepQ- (strain CM89) were examined for the presence of several peptidases previously obtained from strain K-12 in this laboratory. The soluble fraction of each mutant was found to lack the broad-specificity strain K-12 dipeptidase DP and the strain CM89 fraction also lacked activity characteristic of the strain K-12 aminopeptidases AP, L, and OP; like strain CM17, strain CM89 contained the tripeptide-specific aminopeptidase TP. Strain CM89 (but not CM17) appeared to contain little if any activity attributable to the ribosome-bound aminopeptidase I of strain K-12. Whereas loss of DP, AP, OP, and aminopeptidase I activity may be attributed to the pepD-, pepB-, pepN-, and pepA- mutations, respectively, the reason for the loss of L activity remains uncertain. Grown responses of strain CM89 in liquid media containing di- or tripeptides were in accord with absence of enzymes catalyzing rapid hydrolysis of dipeptides. In synthetic liquid media supplemented with the required amino acids per se or with peptone, cultures of both CM strains grew more slowly than strain K-12 and produced smaller cell-yields than those produced by strain K-12.

Direct determination of the properties of peptide transport systems in Escherichia coli, using a fluorescent-labeling procedure

A direct study of peptide uptake by Escherichia coli was made using a fluorescent procedure. After incubation with the bacteria, peptides remaining in the medium were dansylated, separated chromatographically, and quantitated from their fluorescent intensities and/or from their incorporated radioactivity when tritiated dansyl derivatives were prepared. Peptide uptake was apparently not regulated and proceeded continuously until complete, with the absorbed peptides undergoing rapid intracellular hydrolysis and the excess amino acid residues leaving the cell. Thus, peptide uptake and amino acid exodus occur concurrently. However, peptidase-resistant substrates, e.g. triornithine and glycylsarcosine, which can be similarly estimated in cell extracts, were accumulated about 1,000-fold. The influence of amino acid composition and chain length on rates of transport was assessed. Different strains of E. coli showed variability in their rates of di- and oligopeptide transport. With respect to energy coupling, both the di- and oligopeptide permeases behaved like shock-sensitive transport systems.

Peptide hydrolases of Lactobacillus casei: isolation and general properties of various peptidase activities

Discovery of an endopeptidase by gel chromatography and separation of 3 exopeptidases (a dipeptidase, an aminopeptidase and a specific carboxypeptidase) from Lactobacillus casei NCDO 151 by affinity chromatography is described. The 3 exopeptidases were strongly inhibited by the metal chelators EDTA and 1,10-phenanthroline but were reactivated with Co2+ and Mn2+. The pH optima for aminopeptidase, dipeptidase and carboxypeptidase activities were 6.5, 7.6 and 7.2, respectively. Maximum activity was obtained at 45 degrees C for the aminopeptidase, at 30 degrees C for the dipeptidase and at 40 degrees C for the carboxypeptidase. The substrate specificities of the 3 enzymes were also studied. The properties of these 3 enzymes are compared with those of other bacteria.

Photoaffinity inhibition of dipeptide transport in Escherichia coli

A dipeptide containing a nitrene precursor, glycyl-4-azido-2-nitro-L-phenylalanine, has been synthesized. This compound is a photoaffinity inhibitor of dipeptide transport in E. coli. In the dark, the dipeptide is a reversible inhibitor of glycylglycine uptake by live E. coli W cells. The 14C-labeled compound is a substrate for the transport system, with a Km of 7 micrometer and V max of 5 x 10(3) molecules cell-1 s-1 (compare 9 micrometer and 1 x 10(4) molecules cell-1 s-1, respectively, for the transport of glycylglycine under the same conditions). When intact E. coli cells are photolyzed at approximately 350 nm in the presence of the photolabile dipeptide, their ability to transport either glycylglycine or unphotolyzed glycyl-4-azido-2-nitro-L-phenylalanine is irreversibly inhibited, but their ability to transport arginine is unaffected. The presence of glycylglycine in the medium during photolysis protects the cells against the light-dependent inactivation of dipeptide transport.

Transport of [14C]Gly-Pro in a proline peptidase mutant of Salmonella typhimurium

The transport of [14C]Gly-Pro was examined using a mutant of Salmonella typhimurium (strain TN87) deficient in an X-Pro dipeptidase and an X-Pro-Y iminopeptidase. The dipeptide was taken up by one saturable transport system having a Km of 5.3-10(-7)M and a V of 1.4 nmol/mg dry wt cell per min. The uptake of Gly-Pro was not inhibited by amino acids or tripeptides and the transport system exhibited a rather broad side chain specificity for dipeptides. Dipeptides containing hydrophobic residues were the most potent inhibitors of this dipeptide transport system exhibiting Ki values between 10(-8) and 10(-7) M. In contrast, dipeptides containing glycine residues were particularly weak inhibitors. Finally, Gly-Pro was found to be in the intact form inside the cell and was concentrated more than 1000-fold.