Identical Enzyme Research Articles

Changes in peripheral sympathetic outflow of pithed spontaneously hypertensive rats after bradykinin and DesArg-bradykinin infusions: influence of converting-enzyme inhibition.

Because converting enzyme and kininase II are identical enzymes and probably influence both the biosynthesis of angiotensin II and the metabolism of bradykinin, we investigated the effects of bradykinin and desArg-bradykinin on the sympathetic outflow of pithed spontaneously hypertensive rats (SHRs) before and after acute or chronic inhibition of the converting enzyme by ramipril. Sympathetic outflow was induced by preganglionic electrical stimulation of the spinal cord and measured as circulating, stimulation dependent norepinephrine and epinephrine by high-performance liquid chromatography (HPLC) and electrochemical detection. Bradykinin increased dose-dependently norepinephrine and epinephrine release, particularly when converting enzyme was inhibited. DesArg-bradykinin did not influence norepinephrine outflow but caused a dose-dependent increase in epinephrine release only after converting-enzyme inhibition. It is suggested that both bradykinin and desArg-bradykinin could compensate for the lack of effect of angiotensin II on sympathetic outflow.

Appearance of a new trimethoprim resistance gene, dhfrIX, in Escherichia coli from swine.

A new gene, dhfrIX, coding for a trimethoprim-resistant dihydrofolate reductase (DHFR), was found in porcine isolates of Escherichia coli. The new enzyme, DHFR IX, containing 178 amino acids, showed an amino acid similarity of about 26% with DHFR I and the chromosomal DHFR of E. coli K-12. The dhfrIX gene was observed to occur on two distinctly different transferable plasmids, although a fragment of about 2.9 kb, including dhfrIX, had an identical restriction enzyme digestion map in each case. The new plasmid-borne dhfrIX gene mediates resistance to a drug level of only about 250 micrograms/ml, as compared with more than 1,000 micrograms/ml for the more frequently encountered dhfrI gene. The new plasmid-borne trimethoprim resistance gene could have been selected and spread as a consequence of the extensive use of trimethoprim in veterinary practice in Sweden. It will be important to try to follow its possible occurrence in human pathogens as well.

Human liver class III alcohol and glutathione dependent formaldehyde dehydrogenase are the same enzyme

Human liver class III alcohol dehydrogenase (χχ-ADH) and glutathione dependent formaldehyde dehydrogenase are the same enzyme. The enzyme, χχ-ADH, exhibits a k cat of 200 min −1 and a K m of 4 μM for the oxidation of formaldehyde, but only in the presence of GSH. In the absence of GSH the enzyme is essentially inactive toward formaldehyde but very active toward long chain alcohols. Thus, as in the rat (Koivusalo, M., Baumann, M., and Uotila, L. (1989) FEBS Letters 257, 105–109), the class III alcohol dehydrogenase and the GSH dependent formaldehyde dehydrogenase are identical enzymes. S-Hydroxymethyl derivatives of 8-thiooctanoate and lipoate are also very active substrates. The activity is specific for class III alcohol dehydrogenase; neither the class I and II nor the horse EE, ES, and SS isozymes oxidize hemithiolacetals. o-Phenanthroline competitively inhibits both activities and the two substrate types compete with each other.

Characterization of arylsulfatase C isozymes from human liver and placenta

Arylsulfatase C and steroid sulfatase were thought to be identical enzymes. However, recent evidence showed that human arylsulfatase C consists of two isozymes, s and f. In this study, the biochemical properties of the s form partially purified from human placenta were compared with those of the f form from human liver. Only the placental s form has steroid sulfatase activity and hydrolyses estrone sulfate, dehydroepiandrosterone sulfate and cholesterol sulfate. The liver f form has barely detectable activity towards these sterol sulfates. With the artificial substrate, 4-methyllumbelliferyl sulfate, both forms demonstrated a similar K M but the liver enzyme has a pH optimum of 6.9 while the placental form displayed two optima at 7.3 and 5.5. The molecular weight of the native enzyme determined with gel tiltration was 183 000 for the s form and 200 000 for the f form and their p l's were also similar at 6.5. However, the T 50, temperature at which half of the enzyme activity was lost, was 49.5°C for the f form and 56.8°C for the s form. Polyclonal antibodies raised against the placental form reacted specifically against the s and not the f form. They immuno-precipitated concomitantly > 80% of the total placental arylsulfatase C and steroid sulfatase activities while less than 20% of the liver enzyme was immuno-precipitable. In conclusion, the two isozymes s and f of arylsulfatase C in humans purified from placenta and liver, respectively, have similar K M,pI' and native molecular weight. However, they are distinct proteins with different substrate specificity, pH optima, heat-lability and antigenic properties. Only the s form is confirmed to be steroid sulfatase.

Polymerase chain reaction assay for avian polyomavirus.

A polymerase chain reaction assay was developed for detection of budgerigar fledgling disease virus (BFDV). The assay used a single set of primers complementary to sequences located in the putative coding region for the BFDV VP1 gene. The observed amplification product had the expected size of 550 bp and was confirmed to derive from BFDV DNA by its restriction digestion pattern. This assay was specific for BFDV and highly sensitive, being able to detect as few as 20 copies of the virus. By using the polymerase chain reaction, BFDV was detected in adult, nestling, and embryo budgerigar (Melopsitticus undulatus) tissue DNAs and in sera from adult and nestling budgerigars. These results suggest the possibility of persistent infections in adult birds and lend further support to previously described evidence of possible in ovo transmission. BFDV was also detected in chicken embryo fibroblast cell cultures and chicken eggs inoculated with the virus. A 550-bp product with identical restriction enzyme sites was amplified from a suspected polyomavirus isolated from a peach-faced lovebird (Agapornis pesonata) and from tissue DNA from a Hahn's macaw (Ara nobilis) and a sun conure (Aratinga solstitialis) with histological lesions suggestive of polyomavirus infection. These fragments also hybridized with a BFDV-derived probe, proving that they were derived from a polyomavirus very similar, if not identical, to BFDV.

Host range and symptoms are determined by specific domains of the maize streak virus genome

We have cloned two distinct symptomatic variants of the geminivirus maize streak virus from maize plants infected with the Nigerian strain (MSV-N). Following “agroinoculation” to maize plants MSV-Nm produces narrow, mildly chlorotic discontinuous streaks, whereas MSV-Ns-infected tissue has wide, severely chlorotic streaks. Symptom appearance is delayed following MSV-Nm inoculation. MSV-Nm has a narrow host range within the Gramineae comprising a fraction of that of the wide host range isolate MSV-Ns. The two isolates are highly homologous and have identical restriction enzyme maps. In order to localize the determinants of pathogenicity we constructed, in vitro, hybrid genomes by restriction enzyme fragment exchange. The determinants of host range, severity of chlorosis, streak length, and timing of symptom appearance map to a fragment which includes the large intergenic region and the 5′ terminus of the complementary sense C1 gene. Streak width is determined by the virion-sense portion of the genome, which is consistent with the observation that the virion-sense gene products (V1 and V2) are required for spread of the virus.

Different responses between thyroxine 5′-monodeiodinase and protein disulfide isomerase activities to dietary fat and thyroid status in rat liver

On the hypothesis that rat hepatic microsomal type I iodothyronine 5′-monodeiodinase (MDI) would be identical to hepatic protein disulfide isomerase (PDI) (Boado et al. Biochem. Biophys. Res. Commun. 155 1297– 1304 (1988)), we examined the responses of these enzyme activities to dietary fat and thyroid status in rats. The hepatic MDI activity was higher in rats fed high fat diet than in rats fed low fat diet, but the hepatic PDI activity showed the reverse responses to the diets. Propylthiouracil administration (hypothyroidism) lowered the MDI activity, but elevated the PDI activity. Thyroxine administration (hyperthyroidism) elevated the MDI activity but had no effect on the PDI activity. These results indicate that the two enzyme activities are regulated by different mechanisms in vivo , suggesting that MDI and PDI are not identical enzymes.

Proteinase activities in bovine atrium and the possible role of mast cell tryptase in the processing of Atrial Natriuretic Factor (ANF)

1. 1. Using low salt, Triton X-100 and high salt extracts of bovine atria, two main proteinases were identified by means of fluorogenic oligopeptide substrates. 2. 2. An acidic proteinase, extracted in low salt and Triton X-100 was identified as cathepsin B, but it caused little hydrolysis of the Z-Gly-Pro-Arg-containing substrate that resembles the cleavage site for activation of pro-ANF. 3. 3. An alkaline proteinase was extracted only with high salt and had characteristics of the serine proteinase tryptase. It cleaved Z-Gly-Pro-Arg-containing substrates more efficiently than others tested and was localized in and around mast cells histochemically. Previously, Imada et al., 1988 ( J. biol. Chem. 263, 9515–9519) found an identical enzyme would cleave ANF from pro-ANF. 4. 4. These results suggest therefore that mast cell typtase may be involved in the activation of ANF from pro-ANF.

Detection of an alkaline peptidase in Leishmania amastigotes and promastigotes

We have previously characterized a peptidase in Tiypanosomu crirzi that cleaves peptide substrates on the carboxyl side of arginine and lysinc residues at alkaline pH [ I ] . This alkaline peptidase occurs in all stages of the life cycle of T. criizi, and evidence was presented that a similar or identical enzyme was expressed by 15 other species of trypanosomatid, but not by any non-trypanosomatid protozoa or mammalian cells that we tested. The alkaline peptidase of T. criizi is the major enzyme that cleaves Bz-Arg-pNA at pH 8.0. Extracts of six species of Leishmania were found to contain a major alkaline peptidase activity that also cleaves Bz-ArgpNA readily at pH 8.0 [ I ] . This enzyme activity had the same inhibitor and substrate specificity as the 7: cnizi alkaline peptidase in a preliminary investigation. We have now examined the Leishmariiu donovani peptidase that cleaves Bz-Arg-pNA in greater detail. and our findings corroborate our previous data, suggesting that L. donovani does indeed contain an alkaline peptidase very similar t o the T. c r w i enzyme. Detergent extracts of L. donovuni promastigotes were compared with those of amastigotes (prepared from hamster spleens [ 2 ] ) with respect to their ability to cleave a number of peptidyl-p-nitroanilides at pH 8.0, the pH optimum for cleavage of Bz-Arg-pNA. Extracts of both stages of the parasite’s life cycle showed a preference for cleavage of TosGly-Pro-Arg-pNA over Tos-Gly-Pro-Lys-pNA and both generally cleaved longer substrates better than short ones (Table 1 ). Whereas Bz-Arg-pNA was readily cleaved, removal of the N-terminal blocking group, as in Arg-pNA, resulted in considerable reduction in cleavability, although extracts were readily ablc t o cleave Gly-Arg-pNA. The relative rates o f cleavage of different substrates were similar for amastigotes and promastigotes, suggesting that a similar enzyme or enzymes are responsible for hydrolysis of the substrates. The inhibitor profiles for the amastigote and promastigote Bz-Arg-pNA hydrolases were also similar to each other and to the purified T. criizi and C’rithidia jusciciilutu alkaline peptidases (I I I; F. Ashall, D. Harris, H. Roberts. N. Healy & E. Shaw, unpublished work). Thus, the L. doriovarii activity was inhibited by diisopropylfluorophosphate (DFP), TosLys-CH2CI and leupeptin, but was unaffected by phenylmethanesulphonyl fluoride, E64, iodoacetic acid, pepstatin A or 0-phenanthroline. In agreement with a preference for Arg or Lys at PI of substrates, Cbz-Leu-Lys-diazomethane, but not Cbz-Leu-Met-diazomethane, strongly inhibited the enzyme. Since diazomethanes are generally considered to be diagnostic o f cysteine peptidases [ 31 and DFP of serine peptidases 141, the class of peptidase t o which the enzyme belongs remains to be unequivocally determined. The enzyme may be a serine peptidase sensitive to diazomethanes or it may be a cysteine peptidase sensitive to DFP (however, E64 and iodoacetic acid do not inhibit); or it may be a novel class of peptidase.

The use of a drug resistance cartridge for in vitro insertion and deletion mutagenesis of a cosmid clone

A drug-resistant cartridge was employed in the construction of families of insertion mutants of a cosmid clone. The cartridge contains a cml gene and has identical restriction enzyme sites, EcoRI, BamHI, SalI, andPstI, on both ends. The families of mutants were made by ligation of the cartridge to the cosmid, which was linearized or partially digested, followed by in vitro packaging and transduction. From these families we selected cosmid derivatives which either have a unique BamHI site at a predetermined site in the cosmid or have deletions covering different portions of the original clone. The extent of a large gene cluster cloned into the original cosmid was identified by confirming the gene function in some of the deletion mutants. The possibility for further and various uses of this cartridge is discussed.

Effects of Monensin on Subcellular Structure, Thyroglobulin Secretion and Peroxidase Activity of Cultured Thyroid Cells Obtained from Patients with Hyperthyroidism

The effects of monensin on subcellular structure, release of thyroglobulin (TG) and peroxidase (PO) activity were investigated using primary cultures of thyroid cells obtained from patients with Basedow's disease (Basedow's cells). TG concentration in the culture medium was measured by a sandwich enzyme immunoassay and the amount of TG in cultured cells was measured with an identical sandwich enzyme immunoassay after lysis of the cells with Triton X-100. PO activity of cultured cells was measured by a biochemical method. Addition of TSH (10 mU/ml/day) to the culture medium increased the synthesis and release of TG. When monensin (1 micron/l) was added to the medium on the last day of a 3-day incubation with TSH, the Golgi complex showed vacuolative change ultrastructurally, and the amount of intracellular TG was increased, whereas the amount of TG in the culture medium and PO activity became lower than those in the control group. These results suggest that in cultured Basedow's cells, TG is secreted through the Golgi complex, and that the activity of PO is elevated after processing in the Golgi complex.

Intestinal ornithine decarboxylase: half-life and regulation by putrescine

Ornithine decarboxylase (ODC) is the primary rate-limiting enzyme for polyamine synthesis. ODC levels are increased in most tissues, including the intestinal mucosa, by growth-promoting agents. This enzyme has a brief half-life of from 5 to 30 min in mammalian tissues and is regulated by its product; putrescine. The current study examines the turnover and regulation of ODC in the mucosa of the small intestine. With the use of scraped intestinal mucosa from cycloheximide-treated rats, the time course of the decline in ODC activity yielded a half-life of approximately 22 min. Labeling enzyme protein with [3H]difluoromethylornithine (DFMO) resulted in a nearly identical estimation of half-life. ODC activity of mucosa from isolated gut segments stimulated by luminal glycine (0.1-0.4 M) was enhanced 60-100% by 10 mM putrescine administered luminally. Putrescine alone had no effect on ODC. In contrast, 10(-7) M putrescine prevented 80% of the ODC activity stimulated by asparagine in IEC-6 cells (a rat intestinal crypt cell line). The half-life of ODC in unstimulated IEC-6 cells was 20 min and increased to 35 min in cells exposed to 10 mM asparagine. These data demonstrate that ODC of nonproliferating villous cells is regulated differently from the identical enzyme in proliferating crypt cells. Therefore, conclusions regarding mucosal growth should not be based totally on ODC activity from whole mucosa, since it is essentially a measure of only the enzyme present in the villous cells.

Characterisation of an alkaline peptidase of Trypanosoma cruzi and other trypanosomatids

A peptidase activity was purified from extracts of Trypanosoma cruzi on the basis of its ability to cleave benzoyl-arginine-p-nitroanilide. The enzyme was considered to be a cysteine-type peptidase with unusually low sensitivity to E-64. It has a pH optimum of about 8.0 for p-nitroanilides, and cleaves peptide bonds on the carboxyl side of arginine and, to a lesser extent, lysine residues. Cleavage of different substrates occurred at rates that were determined by their catalytic constants (kcat): the peptidase had the same Michaelis constant (about 30 microM) for all substrates tested. Evidence is presented that the peptidase is the major cysteine peptidase in T. cruzi extracts that cleaves p-nitroanilides next to basic amino acid residues at pH 8. The enzyme was detected in all stages of the life cycle of T. cruzi. Furthermore, evidence is presented, based on pH optima, inhibitor sensitivity, substrate specificity and kinetics, and electrophoretic mobility, that a similar or identical enzyme occurs in fifteen other species of trypanosomatid.

Cloning, expression and nucleotide sequence of the gene fragment encoding an antigenic portion of the nucleoside triphosphate hydrolase of Toxoplasma gondii

Toxoplasma gondii expresses high levels of an active nucleoside triphosphate hydrolase (NTPase; EC 3.6.1.3) with several unique properties. It has been detected as a circulating antigen in mice, making it an ideal candidate for diagnostic tests for toxoplasmosis. A cDNA library constructed from T. gondii poly(A) + RNA was made in λgt11. One hundred thousand members of this library were immunoscreened with a rabbit polyclonal antibody to the purified NTPase. Six positive clones were subcloned into the plasmid, pGEX-1N, and the inserts were restriction-mapped. All clones had identical partial restriction enzyme maps. One insert was subcloned into M13mp18 and sequencing by the deoxy/dideoxy method showed an NTPase-encoding gene ( ntp) fragment of 571 bp. The insert was also purified, radiolabelled, and used to hybridize to Northern blots of tachyzoite RNA and quantitative Southern blots of tachyzoite DNA. Northern blotting revealed that the NTPase mRNA was m great abundance and had a length of about 2800 nucleotides. Southern blotting showed a gene copy number of between one and five, and the possibility that ntp is tandemly repeated over a large length of DNA. The NTPase was expressed as a glutathione S-transferase (EC 2.5.1.18) fusion protein of about 50 kDa, which reacted with polyclonal rabbit antibody on Western blotting.

Evidence for the identity of glutathione-dependent formaldehyde dehydrogenase and class III alcohol dehydrogenase

Formaldehyde dehydrogenase (EC 1.2.1.1) is a widely occurring enzyme which catalyzes the oxidation of S-hydroxymethylglutathione, formed from formaldehyde and glutathione, into S-formylglutathione in the presence of NAD. We determined the amino acid sequences for 5 tryptic peptides (containing altogether 57 amino acids) from electrophoretically homogeneous rat liver formaldehyde dehydrogenase and found that they all were exactly homologous to the sequence of rat liver class III alcohol dehydrogenase (ADH-2). Formaldehyde dehydrogenase was found to be able at high pH values to catalyze the NAD-dependent oxidation of long-chain aliphatic alcohols like n-octanol and 12-hydroxydodecanoate but ethanol was used only at very high substrate concentrations and pyrazole was not inhibitory. The amino acid sequence homology and identical structural and kinetic properties indicate that formaldehyde dehydrogenase and the mammalian class III alcohol dehydrogenases are identical enzymes. Formaldehyde dehydrogenase; Alcohol dehydrogenase, class III; Sequence homology; Amino acid sequence

Characterization of a methionine sulfoximine resistant strain ofRhodobacter capsulatusE1F1

A mutant strain of Rhodobacter capsulatus E1 F1 able to grow in the presence of the specific inhibitor l-methionine-d,l-sulfoximine (MSX) has been characterized. The mutant appears to possess an altered MSX transport system. Both, parental and mutant strains showed identical glutamine synthetase (GS) activity and intracellular enzyme levels. Besides, the enzymes from both sources were inactivated in vitro by MSX with a similar rate and presented antigenic identity. On the basis of growth experiments in different nitrogen sources and transport competition tests, we propose that some amino acids (cysteine, serine, leucine, asparagine, glutamate and glutamine) could share a common carrier with MSX. Alanine appears to act as a non competitive inhibitor of mSX transport in R. capsulatus.

Scientific meeting of the Netherlands Society of Child Neurology held in Heeze, 7th of April 1989 : Action myoclonus in progressive myoclonus epilepsy Differential diagnosis and a possible treatment

The twitcher mouse is affected by a disease with pathological features resembling those of human globoid cell leucodystrophy (Krabbe's disease): it also has an identical enzyme deficiency. The progress of the disease has been studied in peripheral nerves. Myelin sheaths develop normally until about the 15th day when the rate of myelination declines.Demyelination, first affecting paranodal regions is seen from the 10th–11th day before clinical signs appear. Krabbe-type inclusions are seen in macrophages and Schwann cells a few days later. Demyelination becomes extensive with increasing age, affecting fibres of all sizes, and axons rapidly remyelinate. Axons are not involved but quantitative studies show that they remain smaller than normal. Changes in twitcher nerves are compared to those in the neuropathy in human Krabbe's disease.

Antioxidant enzyme alterations in experimental and clinical diabetes.

Previous studies from our laboratory have demonstrated the presence of complex alterations in the activities of antioxidant enzymes in various tissues of rats with streptozotocin (STZ)-induced diabetes. In the present investigation, it is shown that rats made diabetic with alloxan (ALX), an agent differing from STZ both chemically and in its mechanism of diabetogenesis, show virtually identical tissue antioxidant enzyme changes which, as is the case with STZ, are preventable by insulin treatment. The finding that the patterns of antioxidant enzyme alterations in chemically-induced diabetes are independent of the diabetogenic agent used and the presence of similar abnormalities in tissues of spontaneously diabetic (BB) Wistar rats (particularly when diabetic control is less than optimal) suggest that the changes observed are a characteristic feature of the uncontrolled diabetic state and that these may be responsible for (or predispose to) the development of secondary complications in clinical diabetes. Comparative studies involving red cells of diabetic rats and human diabetics revealed a number of common changes, namely an increase in glutathione reductase activity, a decreased susceptibility to oxidative glutathione depletion (which was related to the presence of hyperglycemia) and an increased production of malondialdehyde (an indirect index of lipid peroxidation) in response to in vitro challenge with hydrogen peroxide. In the diabetic patients, the extent of this increase in susceptibility of red cell lipids to oxidation paralleled the severity of diabetic complications. Our results suggest that increased (or uncontrolled) oxidative activity may play an important role in the pathogenesis of complications associated with the chronic diabetic state.

Reciprocal renal effects of dopamine and 5-hydroxytryptamine formed within the rat kidney.

1. Clearance of inulin and p-aminohippurate and excretion of water and sodium were measured for eight to 11 clearance periods of 20 min duration in anaesthetized, 3% volume-expanded rats, before and after intravenous infusions of the amino acids L-dopa (L-3,4-dihydroxyphenylalanine) and 5-hydroxytryptophan. During the final two clearance periods, the peripheral decarboxylase inhibitor, carbidopa (S-alpha-hydrazino-3,4-dihydroxy-alpha-methylbenzenepropanoic acid monohydrate), was infused additionally. 2. Renal formation of dopamine (3,4-dihydroxyphenethylamine) and 5-hydroxytryptamine was demonstrated during infusions of L-dopa and 5-hydroxytryptophan, respectively; carbidopa blocked the renal formation of these biogenic amines. 3. During infusion of dopa, a diuresis and a natriuresis were observed; during the infusion of 5-hydroxytryptophan, slight reductions in clearances of inulin and p-aminohippurate, but significant reductions in sodium and water excretion, were measured. 4. The addition of carbidopa diminished diuretic and natriuretic responses to dopa as renal dopamine excretion decreased; the infusion of carbidopa also ameliorated the antinatriuretic and antidiuretic effects of 5-hydroxytryptophan, as 5-hydroxytryptamine excretion decreased. 5. Although dopa and 5-hydroxytryptophan are substrates for the same enzyme, aromatic L-amino-acid decarboxylase, simultaneous infusions of both amino acids at comparable rates gave no evidence of competitive inhibition of amine synthesis. However, the infusion of dopa, after 5-hydroxytryptophan, decreased its antinatriuretic and antidiuretic effects. 6. These data raise the possibility that dopamine and 5-hydroxytryptamine are formed as reciprocal intrarenal hormones by the identical enzyme, aromatic L-amino-acid decarboxylase, which is located within cells of the renal tubule.

Human skin tryptase: purification, partial characterization and comparison with human lung tryptase.

Human skin tryptase was isolated using stepwise low- and high-salt extraction and further purified 448-fold with 33% yield using octyl-Sepharose CL-4B hydrophobic affinity chromatography, Sephacryl S-200 gel filtration and finally octyl-Sepharose CL-4B or cellulose phosphate ion exchange chromatography. The skin tryptase, which has an apparent Mr of 120,000 by gel filtration in high-salt buffer, consisted of polypeptide chains of Mr 34,000 and 38,000 when resolved on SDS gels. Both polypeptide chains, labelled with [3H]diisopropyl fluorophosphate, indicated that they were representative of subunits and that the native proteinase was an aggregate of subunits. However, in some preparations only one band with Mr 34,000 was seen. In low-salt buffer the enzyme was labile and at least 1.4 M KCl was needed to keep the enzyme stabile when incubated at 37 degrees C for 30 min. Heparin glycosaminoglycan partially stabilized the tryptase but addition of protein (e.g. albumin, 80 micrograms/ml) to the tryptase-heparin mixture was needed to keep the enzyme stabile. Tryptases purified by exactly the same method from human lung tissue and from human skin had identical molecular size in gel filtration and in SDS-polyacrylamide gel electrophoresis. They also revealed identical enzyme kinetic parameters with several synthetic peptide substrates. The inhibition profile was identical for both enzymes, and they also crossreacted completely in immunodiffusion plates. These studies strongly indicate that mast cells found in skin as well as lung contain closely related, possible identical trypsin-like proteinases.