Protease I from Escherichia coli. Some physicochemical properties and substrate specificity

Link between allergic asthma and airway mucosal infection suggested by proteinase-secreting household fungi

Active fungal proteinases are powerful allergens that induce experimental allergic lung disease strongly resembling atopic asthma, but the precise relationship between proteinases and asthma remains unknown. Here, we analyzed dust collected from the homes of asthmatic children for the presence and sources of active proteinases to further explore the relationship between active proteinases, atopy, and asthma. Active proteinases were present in all houses and many were derived from fungi, especially Aspergillus niger. Proteinase-active dust extracts were alone insufficient to initiate asthma-like disease in mice, but conidia of A. niger readily established a contained airway mucosal infection, allergic lung disease, and atopy to an innocuous bystander antigen. Proteinase produced by A. niger enhanced fungal clearance from lung and was required for robust allergic disease. Interleukin 13 (IL-13) and IL-5 were required for optimal clearance of lung fungal infection and eosinophils showed potent anti-fungal activity in vitro. Thus, asthma and atopy may both represent a protective response against contained airway infection due to ubiquitous proteinase-producing fungi.

Functional role of a non-active site residue Trp(23) on the enzyme activity of Escherichia coli thioesterase I/protease I/lysophospholipase L(1)

Escherichia coli possesses a versatile protein with the enzyme activities of thioesterase I, protease I, and lysophospholipase L(1). The protein is dubbed as TAP according to the chronological order of gene discovery (TesA/ApeA/PldC). Our previous studies showed that TAP comprises the catalytic triad Ser(10), Asp(154), and His(157) as a charge relay system, as well as Gly(44) and Asn(73) residues devoted to oxyanion hole stabilization. Geometrically, about 10 A away from the enzyme catalytic cleft, Trp(23) showed a stronger resonance shift than the backbone amide resonance observed in the nuclear magnetic resonance (NMR) analyses. In the present work, we conducted site-directed mutagenesis to change Trp into alanine (Ala), phenylalanine (Phe), or tyrosine (Tyr) to unveil the role of the Trp(23) indole ring. Biochemical analyses of the mutant enzymes in combination with TAP's three-dimensional structures suggest that by interlinking the residues participating in this catalytic machinery, Trp(23) could effectively influence substrate binding and the following turnover number. Moreover, it may serve as a contributor to both H-bond and aromatic-aromatic interaction in maintaining the cross-link within the interweaving framework of protein.

Enhanced preference for pi-bond containing substrates is correlated to Pro110 in the substrate-binding tunnel of Escherichia coli thioesterase I/protease I/lysophospholipase L(1)

Escherichia coli thioesterase I/protease I/lysophospholipase L(1) (TAP) possesses multifunctional enzyme with thioesterase, esterase, arylesterase, protease, and lysophospholipase activities. Leu109, located at the substrate-binding tunnel, when substituted with proline (Pro) in TAP, shifted the substrate-preference from medium-to-long acyl chains to shorter acyl chains of triglyceride and p-nitrophenyl ester, and increased the preference for aromatic-amino acid-derived esters. In the three-dimensional TAP structures, the only noticeable alteration of backbone and side chain conformation was located at the downstream Pro110-Ala123 region rather than at Pro109 itself. The residue Pro110, adjacent to Leu109 or Pro109, was found to contribute to the substrate preference of TAP enzymes for esters containing acyl groups with pi bond(s) or aromatic group(s). Some of the interactions between the enzyme protein and the substrate may be contributed by an attractive force between the Pro110 C-H donor and the substrate pi-acceptor.

Functional role of catalytic triad and oxyanion hole-forming residues on enzyme activity of Escherichia coli thioesterase I/protease I/phospholipase L1

Escherichia coli TAP (thioesterase I, EC 3.1.2.2) is a multifunctional enzyme with thioesterase, esterase, arylesterase, protease and lysophospholipase activities. Previous crystal structural analyses identified its essential amino acid residues as those that form a catalytic triad (Ser10-Asp154-His157) and those involved in forming an oxyanion hole (Ser10-Gly44-Asn73). To gain an insight into the biochemical roles of each residue, site-directed mutagenesis was employed to mutate these residues to alanine, and enzyme kinetic studies were conducted using esterase, thioesterase and amino-acid-derived substrates. Of the residues, His157 is the most important, as it plays a vital role in the catalytic triad, and may also play a role in stabilizing oxyanion conformation. Ser10 also plays a very important role, although the small residual activity of the S10A variant suggests that a water molecule may act as a poor substitute. The water molecule could possibly be endowed with the nucleophilic-attacking character by His157 hydrogen-bonding. Asp154 is not as essential compared with the other two residues in the triad. It is close to the entrance of the substrate tunnel, therefore it predominantly affects substrate accessibility. Gly44 plays a role in stabilizing the oxyanion intermediate and additionally in acyl-enzyme-intermediate transformation. N73A had the highest residual enzyme activity among all the mutants, which indicates that Asn73 is not as essential as the other mutated residues. The role of Asn73 is proposed to be involved in a loop75-80 switch-move motion, which is essential for the accommodation of substrates with longer acyl-chain lengths.

Crystal structure of Escherichia coli thioesterase I/protease I/lysophospholipase L1: consensus sequence blocks constitute the catalytic center of SGNH-hydrolases through a conserved hydrogen bond network

Escherichia coli thioesterase I (TAP) is a multifunctional enzyme possessing activities of thioesterase, esterase, arylesterase, protease, and lysophospholipase. In particular, TAP has stereoselectivity for amino acid derivative substrates, hence it is useful for the kinetic resolution of racemic mixtures of industrial chemicals. In the present work, the crystal structure of native TAP was determined at 1.9A, revealing a minimal SGNH-hydrolase fold. The structure of TAP in complex with a diethyl phosphono moiety (DEP) identified its catalytic triad, Ser10-Asp154-His157, and oxyanion hole, Ser10-Gly44-Asn73. The oxyanion hole of TAP consists of three residues each separated from the other by more than 3.5A, implying that all of them are highly polarized when substrate bound. The catalytic (His)C(epsilon1)-H...O=C hydrogen bond usually plays a role in the catalytic mechanisms of most serine hydrolases, however, there were none present in SGNH-hydrolases. We propose that the existence of the highly polarized tri-residue-constituted oxyanion hole compensates for the lack of a (His)C(epsilon1)-H...O=C hydrogen bond. This suggests that members of the SGNH-hydrolase family may employ a unique catalytic mechanism. In addition, most SGNH-hydrolases have low sequence identities and presently there is no clear criterion to define consensus sequence blocks. Through comparison of TAP and the three SGNH-hydrolase structures currently known, we have identified a unique hydrogen bond network which stabilizes the catalytic center: a newly discovered structural feature of SGNH-hydrolases. We have defined these consensus sequence blocks providing a basis for the sub-classification of SGNH-hydrolases.

The apeE gene of Salmonella typhimurium encodes an outer membrane esterase not present in Escherichia coli

Salmonella typhimurium apeR mutations lead to overproduction of an outer membrane-associated N-acetyl phenylalanine beta-naphthyl ester-cleaving esterase that is encoded by the apeE gene (P. Collin-Osdoby and C. G. Miller, Mol. Gen. Genet. 243:674-680, 1994). This paper reports the cloning and nucleotide sequencing of the S. typhimurium apeE gene as well as some properties of the esterase that it encodes. The predicted product of apeE is a 69.9-kDa protein which is processed to a 67-kDa species by removal of a signal peptide. The predicted amino acid sequence of ApeE indicates that it is a member of the GDSL family of serine esterases/lipases. It is most similar to a lipase excreted by the entomopathogenic bacterium Photorhabdus luminescens. The Salmonella esterase catalyzes the hydrolysis of a variety of fatty acid naphthyl esters and of C6 to C16 fatty acid p-nitrophenyl esters but will not hydrolyze peptide bonds. A rapid diagnostic test reported to be useful in distinguishing Salmonella spp. from related organisms makes use of the ability of Salmonella to hydrolyze the chromogenic ester substrate methyl umbelliferyl caprylate. We report that the apeE gene product is the enzyme in Salmonella uniquely responsible for the hydrolysis of this substrate. Southern blot analysis indicates that Escherichia coli K-12 does not contain a close analog of apeE, and it appears that the apeE gene is contained in a region of DNA present in Salmonella but not in E. coli.

Mutations affecting a regulated, membrane-associated esterase in Salmonella typhimurium LT2

Mutations at the apeA locus in Salmonella typhimurium lead to loss of a soluble enzyme ("protease I") that hydrolyzes the chromogenic endoprotease substrate N-acetyl phenylalanine beta-naphthyl ester. We have isolated pseudorevertants of S. typhimurium apeA mutations that have regained the ability to hydrolyze this compound. These pseudorevertants contain mutations (apeR) that lead to overproduction of a membrane-bound esterase different from protease I. The apeR locus is phage P1 cotransducible with ilvC (83 map units) and is unlinked to apeA. Mutations at still another locus, apeE, lead to loss of the membrane-associated esterase. The apeE locus is P1 cotransducible with purE (12 map units). In an apeE-lacZ operon fusion strain, an apeR mutation increases the level of beta-galactosidase approximately 60-fold. We propose that apeR encodes a repressor of apeE. The evidence available suggests that the ApeE protein is not a protease.

"Protease I" of Escherichia coli functions as a thioesterase in vivo

Escherichia coli protease I is assayed as an esterase active with certain synthetic model chymotrypsin substrates. However, the gene encoding protease I has the same DNA sequence and genomic location as tesA, a gene that encodes E. coli thioesterase I. We report that both hydrolase activities utilize the same active site and demonstrate that the protein functions as a thioesterase in vivo.

Families of serine peptidases

This chapter examines families of serine peptidases. Serine peptidases are found in viruses, bacteria, and eukaryotes. They include exopeptidases, endopeptidases, oligopeptidases, and omega peptidases. On the basis of three-dimensional structures, most of the serine peptidase families can be grouped together into about six clans that may have common ancestors. The structures are known for members of four of the clans, chymotrypsin, subtilisin, carboxypeptidase C, and Escherichia D-Ala-D-Ala peptidase A. The peptidases of chymotrypsin, subtilisin, and carboxypeptidase C clans have a common “catalytic triad” of three amino acids—namely, serine (nucleophile), aspartate (electrophile), and histidine (base). The geometric orientations of these are closely similar between families; however the protein folds are quite different. The arrangements of the catalytic residues in the linear sequences of members of the various families commonly reflect their relationships at the clan level. The members of the chymotrypsin family are almost entirely confined to animals. 10 families are included in chymotrypsin clan (SA), and all the active members of these families are endopeptidases. The order of catalytic residues in the polypeptide chain in clan SA is His/Asp/Ser.

Molecular cloning, sequencing, and mapping of the gene encoding protease I and characterization of proteinase and proteinase-defective Escherichia coli mutants

Clones carrying the gene encoding a proteinase were isolated from Clarke and Carbon's collection, using a chromogenic substrate, N-benzyloxycarbonyl-L-phenylalanine beta-naphthyl ester. The three clones isolated, pLC6-33, pLC13-1, and pLC36-46, shared the same chromosomal DNA region. A 0.9-kb Sau3AI fragment within this region was found to be responsible for the overproduction of the proteinase, and the nucleotide sequence of the region was then determined. The proteinase was purified to homogeneity from the soluble fraction of an overproducing strain possessing the cloned gene. N-terminal amino acid sequencing of the purified protein revealed that the cloned gene is the structural gene for the protein, with the protein being synthesized in precursor form with a signal peptide. On the basis of its molecular mass (20 kDa), periplasmic localization, and substrate specificity, we conclude this protein to be protease I. By using the gene cloned on a plasmid, a deletion mutant was constructed in which the gene was replaced by the kanamycin resistance gene (Kmr) on the chromosome. The Kmr gene was mapped at 11.8 min, the gene order being dnaZ-adk-ush-Kmr-purE, which is consistent with the map position of apeA, the gene encoding protease I in Salmonella typhimurium. Therefore, the gene was named apeA. Deletion of the apeA gene, either with or without deletion of other proteinases (protease IV and aminopeptidase N), did not have any effect on cell growth in the various media tested.

Proteases and protein degradation in Escherichia coli

In E. coli, protein degradation plays important roles in regulating the levels of specific proteins and in eliminating damaged or abnormal proteins. E. coli possess a very large number of proteolytic enzymes distributed in the cytoplasm, the inner membrane, and the periplasm, but, with few exceptions, the physiological functions of these proteases are not known. More than 90% of the protein degradation occurring in the cytoplasm is energy-dependent, but the activities of most E. coli proteases in vitro are not energy-dependent. Two ATP-dependent proteases, Lon and Clp, are responsible for 70-80% of the energy-dependent degradation of proteins in vivo. In vitro studies with Lon and Clp indicate that both proteases directly interact with substrates for degradation. ATP functions as an allosteric effector promoting an active conformation of the proteases, and ATP hydrolysis is required for rapid catalytic turnover of peptide bond cleavage in proteins. Lon and Clp show virtually no homology at the amino acid level, and thus it appears that at least two families of ATP-dependent proteases have evolved independently.

Periplasmic proteases of Escherichia coli

In the course of examining the turnover of enzymes and proteins subject to catabolite inhibition and/or catabolite repression in Escherichia coli, we have observed at least three novel calcium- or manganese-activated proteolytic activities restricted to the periplasmic space. The occurrence and level of these proteolytic activities vary with the stage of cell growth and carbon source. Each of these proteases are neutral metalloendoproteases capable of degrading test substrates such as casein, insulin, globin, and protamine and appear to be unique when compared with the known periplasmic proteases in E. coli. One of these proteases (designated protease VII) has been purified to homogeneity and characterized in regard to subunit structure, sensitivity to protease inhibitors and metal ions, and substrate specificity. Immunological and genetic approaches are being employed to determine if these novel proteases arise from a common gene product. The physiological role of these proteases remains to be established.

Pancreatic and granulocytic endoproteases in faecal extracts from patients with active ulcerative colitis

Faecal samples from 16 patients with acute attacks of ulcerative colitis, 7 with quiescent disease, and 8 healthy subjects were studied with regard to extractable amounts of casein digestion capacity, immunoreactive anionic trypsin, cationic trypsin, chymotrypsin, pancreatic elastase, and granulocytic elastase. Patients with acute attacks of colitis had significantly higher levels of casein digestion, pancreatic elastase, and granulocytic elastase in faecal samples than patients with quiescent disease and controls. The non-specific proteolytic activity in faecal extracts from patients with acute colitis was mainly due to the pancreatic proteases anionic elastase, cationic elastase, and anionic trypsin to the granulocytic proteases elastase and neutral protease. These active proteases may cause further destruction of the already damaged mucosa found in patients with severe ulcerative colitis.

Properties and proteolysis of ferric enterobactin outer membrane receptor in Escherichia coli K12

A protein with a relative subunit molecular weight of 81000 (81K) has been isolated in virtually pure form from the outer membrane of low iron grown cells of Escherichia coli K12. The 81K protein, which is part of the receptor complex for translocation of the siderophore ferric enterobactin, displays activity in vitro for binding both ferric enterobactin and colicin B. The dissociation constant for the 81K-ferric enterobactin compound at 4 degrees C in 2% Triton-0.1 M Tris, pH 7, was determined to be 10 nM. The N-terminal amino acid was identified as phenylalanine, and the amino acid composition was shown to be similar to that published for the ferric aerobactin-cloacin receptor of Enterobacter cloacae. A plasmid-bearing strain of E. coli was employed to confirm that degradation of 81K to a slightly smaller, inactive form (81K) is performed by a second outer membrane component, protein a. The endoproteolytic action of protein a was verified by the finding of alanine as the N-terminal residue of 81K. A survey of enteric species suggests that the 81K-protein a interaction is confined to the K12 strain of E. coli.

Subcellular distribution of various proteases in Escherichia coli

It has been reported recently that Escherichia coli cells contain eight distinct soluble enzymes capable of degrading proteins to acid-soluble material. Two are metalloproteases that degrade [125I]insulin but not larger proteins: protease Pi, which is identical to protease III, is restricted to the periplasm, and protease Ci is restriction to the cytoplasm. The six others (named Do, Re, Mi, Fa, So, and La, which is the ATP-dependent protease) are serine proteases that degrade [14C]globin and [3H]casein, but not insulin. One of these (Mi) is localized to the periplasm, and one (Re) is distributed equally between the two cellular fractions. The others are present only in the cytoplasm.

Identification and localization of two membrane-bound esterases from Escherichia coli

Hydrolytic activities of isolated membrane fractions of Escherichia coli against chromogenic substrates, p-nitrophenyl ester and beta-naphthyl ester derivatives of N-substituted amino acids, were investigated by spectrophotometric and electrophoretic methods. Although detergents were absolutely necessary for the solubilization of enzymes, the amount of solubilized activities was increased by adding salt, such as NaCl or KCl. Two esterases were identified and separated by PAGE and by chromatography of the solubilized proteins in the presence of detergent. One hydrolyzed the alanine derivatives preferentially, whereas the other was mainly active on phenylalanine derivatives. Only the first was inactivated by diisopropyl fluorophosphate, a serine hydrolase inhibitor. Whereas the chymotrypsin-like enzyme was equally distributed between the inner and the outer membrane, the alanine activity was only detected in the inner membrane. They were both resistant to extraction with high salt concentrations, indicating their integral association with membranes. A study of the accessibility of these enzymes to their substrate in membrane vesicles with known polarity suggests that both alanine and phenylalanine activities are localized near the external surface of the cytoplasmic (inner) membrane. However, the phenylalanine activity (chymotrypsin-like enzyme) appears to be deeply buried inside the outer membrane. Because of its insensitivity to diisopropyl fluorophosphate, this last esterase seems to be distinct from the previously isolated periplasmic endopeptidase, protease I, which is also a chymotrypsin-like enzyme.

Isolation and characterization of proteases from Bacteroides melaninogenicus

We isolated two types of intracellular proteases from a strain of Bacteroides melaninogenicus. These enzymes were extracted from cells by ultrasonic treatment and were partially purified. These two enzymes (proteases I and II) differed in molecular weight, heat stability, sensitivity to reducing agents, Km value, and optimum pH for activity.

Isolation of a second rifamycin-binding from Escherichia coli by affinity chromatography

When extracts of Escherichia coli are filtered through a Sepharose column containing covalently bound rifamycin a protein is bound which can be eluted either with a high concentration of urea or more specifically with low concentrations of rifamycins. Its Mr is 18,000 +/- 1,000 in the presence of dodecylsulfate, in its absence 36,000 +/- 3,000. The association constant of the protein for rifampicin is 2.4 +/- 0.5 x 10(-4) M with two binding sites per dimer as determined by equilibrium dialysis. Large amounts of this protein are released from the cells by an osmotic shock.

Secretion and membrane localization of proteins in Escherichia coli

The envelope of Escherichia coli consists of two distinct membranes, the outer membrane and the cytoplasmic membrane. The space between the two membranes is called the periplasmic space, and each fraction contains its own specific proteins. In this review, it is discussed how proteins are localized in their final locations in the envelope. Proteins localized in the outer membrane and the periplasmic space as well as transmembranous proteins in the cytoplasmic membranes appear to be produced from their precursors which have peptide extensions of about 20 amino acid residues at the amino terminal ends. General features for the peptide extension are deduced from the known sequences of the peptide extensions, and, based on their known properties, a hypothesis (loop model) is proposed to explain the possible functions of the peptide extension during the mechanism of secretion across the cytoplasmic membrane.

Acylaminoacid esterase mutants of Salmonella typhimurium

Salmonella typhimurium contains three electrophoretically separable enzyme activities that hydrolyze N-acetyl phenylalanine beta-naphthyl ester (NAPNE). One of these enzymes is an endoprotease, protease I. Mutations at a locus apeA near purE lead to loss of this enzyme. We have found that N-acetyl leucine alpha-naphthyl ester (NALNE) is not hydrolyzed by protease I but is a good substrate for the other two activities. Using NALNE as a chromogenic substrate to screen colonies growing on agar, we have isolated mutants (apeB) that simultaneously lose both of the two other esterase activities. The chromosomal positions of apeB and nearby markers in the proC-purE region have been determined using both phage P1 and phage P22 mediated transduction. The observed order is proC thiC apeB apt apeA purE. Strains lacking all three activities (apeA apeB double mutants) have been constructed and have growth rates similar to wild-type strains.

Salmonella typhimurium mutants lacking protease II

Mutants of Salmonella typhimurium lacking protease II, an endoprotease with trypsin-like specificity, have been isolated. These mutants can be identified by using the chromogenic substrate N-methyl-N-p-toluenesulfonyl-L-lysine beta-naphthyl ester to screen colonies growing on agar for the presence of the enzyme. All of the mutations isolated map at locus tlp (typsin-like protease) which is cotransducible (approximately 1%) using phage P1 with tre (trehalose utilization) at approximately 58 min on the Salmonella map. Double mutants lacking both protease I and protease II have been constructed. These strains grew normally. They were able to degrade abnormal proteins and to carry out protein turnover during carbon starvation at the same rate as the wild type.

Intracellular serine protease of Bacillus subtilis: sequence homology with extracellular subtilisins

Intracellular serine protease was isolated from stationary-grown Bacillus subtilis A-50 cells and purified to homogeneity. The molecular weight of the enzyme is 31,000 +/- 1,000, with an isoelectric point of 4.3. Its amino acid composition is characteristically enriched in glutamic acid content, differing from that of extra-cellular subtilisins. The enzyme is completely inhibited with phenylmethylsulfonyl fluoride and ethylenediaminetetraacetic acid. Intracellular protease possesses negligible activity towards bovine serum albumin and hemoglobin, but has 5- to 20-fold higher specific activity against p-nitroanilides of benzyloxycarbonyl tripeptides than subtilisin BPN'. Esterolytic activity of the enzyme is also higher than that of subtilisin BPN'. The enzyme is sequence homologous with secretory subtilisins throughout 50 determined NH2-terminal residues, indicating the presence of duplicated structural genes for serine proteases in the B. subtilis genome. The occurrence of two homologous genes in the cell might accelerate the evolution of serine protease not only by the loosening of selective constrainst, but also by creation of sequence variants by means of intragenic recombination. Three molecular forms of intracellular protease were found, two of them with NH2-terminal glutamic acid and one minor form, three residues longer, with asparagine as NH2 terminus. These data indicate the possible presence of an enzyme precursor proteolytically modified during cell growth.

Immunochemical analysis of inner and outer membranes of Escherichia coli by crossed immunoelectrophoresis

Isolated membrane fractions of Escherichia coli K-12 yielded complex immunoprecipitate patterns when Triton X-100 and sodium dodecyl sulfate extracts were examined by crossed immunoelectrophoresis with antienvelope immunoglobulins. Twelve of the 46 antigens in the immunoprecipitate patterns of inner (plasma) membranes were identified by zymograms and/or by the use of specific antisera. The following enzyme activities were detected in immunoprecipitates: 6-phosphogluconate dehydrogenase (EC 1.1.1.43); adenosine triphosphatase (EC 3.6.1.3); glutamate dehydrogenase (EC 1.4.1.4), two separate components; malate dehydrogenase (EC 1.1.1.37); dihydroorotate dehydrogenase (EC 1.3.3.1); succinate dehydrogenase (EC 1.3.99.1); lactate dehydrogeanse (EC 1.1.1.27); reduced nicotinamide adenine dinucleotide dehydrogenase (EC 1.6.99.3); protease (EC 3.4.21.1); and glycerol 3-phosphate dehydrogenase (EC 1.1.99.5). The corresponding immunoprecipitate pattern for isolated outer membranes consisted of at least 25 discrete antigens and differed strikingly from that obtained with inner membranes. Two major immunogens were identified as lipopolysaccharide and Braun lipoprotein. A protease-active immunoprecipitate was also detected in this fraction, but attempts to identify the Rosenbusch matrix protein in the crossed immunoelectrophoretic profile were unsuccessful.

Purification and properties of a periplasmic protein related to sn-glycerol-3-phosphate transport in Escherichia coli

Protein GLPT, a periplasmic protein previously recognized as closely related to the active transport of sn-glycerol-3-phosphate in Escherichia coli was isolated by the cold osmotic shock procedure. It was purified by Sephadex chromatography and isoelectric focussing. The purified protein does not exhibit any detectable binding activity toward sn-glycerol-3-phosphate. It has no activity as a glycerol phosphatase nor as a glycerol kinase. Polyacrylamide gel electrophoresis in the presence of dodecylsulfate of the protein subsequent to treatment in urea, boiling in dodecylsulfate and crosslinking indicates that it occurs as an oligomeric protein composed of four identical subunits of 40 000 molecular weight. Membrane vesicles of wild-type strains that contain protein GLPT in whole cells loose it during vesicle preparation. However, they still exhibit high transport activity toward sn-glycerol-3-phosphate. Membrane vesicles prepared from glp T mutants that may or may not contain protein GLPT do not transport sn-glycerol-3-phospahte. We conclude from these results that protein GLPT does not participate in the energy-dependent active transport through the cytoplasmic membrane but could be involved in facilitating the diffusion of sn-glycerol-3-phosphate through the outer layers of E. coli.

Immunochemical quanitation of pancreatic endopeptidases in the intestinal contents of germfree and conventional rats

Two electrophoretically distinct trypsins and chymotrypsins and an elastolytic enzyme were isolated from rat pancreatic juice. Rabbit antisera against these enzymes were produced, and with an immunochemical technique the trypsins, chymotrypsins, and elastase were studied in the intestinal contents of conventional and germfree rats. In both types of rat the anionic trypsin and chymotrypsin were the most abundant and found in higher concentrations in the distal than in the proximal small intestine. The cecal and fecal concentrations of anionic trypsin were markedly higher in the germfree rat when compared to the conventional rat. Cymotrypsin was undetectable in the large intestine of either the conventional or germfree rat when this technique was used. Immunoreactive elastase was found in greater amounts in the distal small intestine, and high concentrations were demonstrated in the cecal contents and feces of the germfree rat. In contrast, no immunoreactive elastase was detected in the large intestine of the conventional rat. Gel filtration indicated that the immunoreactive anionic trypsin and elastase found in fecal extracts were of about the same molecular size as the native enzymes. The findings suggest that the intestinal microflora is instrumental in the inactivation and degradation of pancreatic trypsin and elastase but not chymotrypsin.

Elevated fecal levels of endogenous pancreatic endopeptidases after antibiotic treatment

Feces from normal and antibiotic-treated persons were analyzed for the content of immunoreactive trypsin and elastase. In the control group the mean concentration of immunoreactive trypsin was 13 microgram per g feces as compared to 147 in the antibiotic-treated group. Elastase was demonstrable in only 3 of 30 samples in the control group but in 20 of 26 in the antibiotic-treated group. The decreased inactivation of pancreatic proteases must depend on an altered intestinal microflora. The results suggest that reestablishment of a normal enteric flora may take months after the short time oral administration of antibiotics.