Isolation and immunological studies of high and low molecular weight cysteine proteinase inhibitors in bovine serum

Two kinds of cysteine proteinase inhibitor (M_r 145 000 and M_r 15 500) were purified from bovine serum. These purified inhibitors showed a single band on SDS-polyacrylamide gel electrophoresis, respectively. The isoelectric point of the high molecular weight inhibitor was found to be 4.4 and that of the low molecular weight inhibitor was 8.6. The high molecular weight inhibitor inhibited papain and cathepsin H, but had little activity against cathepsin B. While the low molecular weight inhibitor was a strong inhibitor of papain and cathepsin H and showed a weak inhibition of cathepsin B. These two inhibitors showed different immunological reactivities.     

Localization of the thermosensitive X-prolyl dipeptidyl aminopeptidase in the vacuolar membrane of Saccharomyces cerevisiae

Most of the X-prolyl dipeptidyl aminopeptidase activity of Saccharomyces cerevisiae was found to be associated with purified vacuolar membranes (specific activity approx. 75-times higher than in the protoplast lysate). The tonoplast-bound enzyme is thermosensitive. Another heat-resistant enzyme was found in the protoplast lysate. The tonoplast-bound thermosensitive enzyme shows an apparent Km of 0.06 mM against L-alanyl-L-prolyl-p-nitroanilide while the heat-resistant enzyme shows an apparent Km of 0.4 mM against the same substrate.     

Insulin degradation by human skeletal muscle

Although previous studies from this and other laboratories have extensively characterized insulin degrading activity in animal tissues, little information has been available on insulin responsive human tissues. The present study describes the insulin degrading activity in skeletal muscle from normal human subjects. Fractionation of a sucrose homogenate of skeletal muscle demonstrated that 97% of the total neutral insulin degrading activity was in the 100 000 × g supernatant with no detectable glutathione-insulin transhydrogenase activity. The 100 000×g pellet contained 85% of the total acid protease activity and all the glutathione-insulin transhydrogenase activity. The soluble insulin degrading activity was purified 1400-fold by ammonium sulfate fractionation, molecular exclusion, ion-exchange and affinity chromatography. Enzymatic activity was determined by measuring an increase in trichloroacetic acid-soluble products of the ¹²⁵I-labeled hormone substrates. The purified enzyme showed marked proteolytic specificity for insulin with a K_m of 1.63·10^?7 M (±0.32) and was competitively inhibited by proinsulin and glucagon with K_i values of 2.1 · 10?⁶ M and 4.0 · 10^?6 M, respectively. This insulin protease exhibited a pH optimum between 7 and 8, a molecular weight of 120 000 and was capable of degrading glucagon. Inhibition studies demonstrated that a sulfhydryl group is essential for activity. Molecular exclusion chromatography of [¹²⁵I]insulin degraded products revealed a time-dependent increase in degradation products with molecular weights intermediate between intact insulin and iodotyrosine. These studies demonstrate that the major enzymatic system responsible for insulin degrading activity is a soluble cysteine protease capable of rapidly metabolizing insulin under physiologic conditions.     

Protease inhibitors in the alimentary tract of the medicinal leech Hirudo medicinalis: In vivo and in vitro studies

Summary In individual leeches the flux of labeled serum through the digestive tract was monitored to measure the rate of digestion. A mean value of 10 mg of the original serum (or 2–3 mg of the contents of the foregut) per individual per day was found, which was constant during 10 weeks. On average the serum remained in the intestinum for 20 days. Occurrence and concentrations of eglin and bdellin, specific proteinase inhibitors of Hirudo, were analyzed after various periods following the ingestion of a meal. In the foregut they were present immediately after feeding. Their quantities increased several-fold within a few weeks. In the intestinum the tests for these inhibitors were always negative. The inhibition of the proteolytic activity of intestinum preparations by eglin, bdellin, and foregut extract was tested in vitro. Using azo-albumin as (an unspecific) substrate, inhibition by eglin was maximally 25% and by bdellin 60%. When the quantitative relations presumably representing in vivo conditions were applied, only a slight inhibition of proteolysis occurred. A hypothetical role of the inhibitors in the preservation of the blood stored in the foregut is discussed.Abbreviations BIGGANA N-benzoyl-isoleucyl-glutaryl-glycyl-arginyl-4-nitroanilide - SAPPNA N-succinyl-alanyl-alanyl-prolyl-phenylalanyl-4-nitroanilide - TPCK tosyl-phenylalanyl-chloromethyl-detone - TRIS tris-(hydroxymethyl)aminomethane     

Degradation of the four monoiodoinsulin isomers by the insulin protease of rat liver

The cleavage of insulin by the partially purified insulin protease was studied using the four [¹²⁵I]tyrosine-monoiodoinsulins (tyrosine A-14 and A-19 of the A-chain; tyrosine B-16 and B-26 of the B-chain). The rates of conversion of the four isomers to trichloroacetic acid-soluble form was in the order B-26 > A-14 > A-19 > B-16. The following was observed in experiments which gave 19/14/5/3 percent conversion to trichloroacetic acid-soluble products: the loss of ability to bind to IM-9 lymphocytes was approx. 55% for all four isomers. About 70% of the radioactivity was in the ‘insulin’ peak, and about 30% was in peptides smaller than insulin as judged by gel filtration on Sephadex G-50. The descending limb of the ‘insulin’ peak contained significant amounts of radioactive material not binding to IM-9 lymphocytes. This material showed multiple peaks when applied to high performance liquid chromatography. Other experiments were designed to cause an almost complete degradation of the isomers. Under these conditions, the radioactivity eluted on Sephadex G-50 largely as iodotyrosine (and some small peptides) using the A-14, B-16 and B-26 isomers, whereas iodotyrosine was absent using the A-19 isomer. Thus, the insulin protease appears to first degrade insulin to multiple products with molecular sizes slightly smaller than insulin and subsequently to small peptides (e.g. containing tyrosine A-19) and amino acids (e.g. tyrosine A-14, B-16 and B-26).     

Proteinase activity in potato plants

Several vegetative tissues of potato plants were screened for proteinase activity. Both endopeptidase and exopeptidase activities were investigated using gelatin and L-amino acid-4-nitroanilides (benzoyl-L-arginine-4-nitroanilide/BAPA, glutaryl-L-phenyl-alanine-4-nitroanilide/GLUPHEPA, alanine-4-nitro-anilide/APA, leucine-4-nitroanilide/LPA, and benzoyl-L-tyrosine-4-nitroanilide/BTPA) as substrates. Leaves and rootes were found to contain the highest levels of endopeptidase activity; lesser activities were detected in flower petals, sprouts, and tubers. Three different types of proteinases, L-BAPAase (serine proteinase), APAase (thiol proteinase), and BTPAase (sensitive to reducing agents), were characterized in various physical and chemical properties. Their temperature optima were determined to be 25° (L-BAPAase) and 40° (BTPAase, APAase) respectively; their pH optimum was between 8.6 and 9.0, their isoelectric points were between pH 4.25 and 6.0, and their molecular weight was estimated 70,000 (L-BAPAase, APAase) and between 150,000–250,000 (BTPAase). The trypsin-like activity against L-BAPA was inhibited by diisopropylfluorophosphate and by tosyllysine-chloromethyl ketone, but not by trypsin inhibitors from potato and legume.Abbreviations APA alanine-4-nitroanilide - BAPA benzoyl-L-arginine-4-nitroanilide - BTPA benzoyl-L-tyrosine-4-nitroanilide - DFP diisopropylfluorophosphate - DMF dimethyl formamide - EDTA ethylenedinitrilotetraacetic acid - GLUPHEPA glutaryl-L-phenylalanine-4-nitroanilide - LPA leucine-4-nitroanilide - PHMB p-hydroxy-mercuribenzoate - PI-I potato chymotrypsin inhibitor I - PPI potato proteinase leaf - PPr potato proteinase root - PPt potato proteinase tuber - PVP polyvinylpyrrolidone - TLCK tosyl-L-lysinechloromethyl ketone - TPCK tosyl-L-phenylalanyl chloromethane     

Cryo-EM Structure of the Full-length hnRNPA1 Amyloid Fibril

Heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) is a multifunctional RNA-binding protein that is associated with neurodegenerative diseases, such as amyotrophic lateral sclerosis and multisystem proteinopathy. In this study, we have used cryo-electron microscopy to investigate the three-dimensional structure of amyloid fibrils from full-length hnRNPA1 protein. We find that the fibril core is formed by a 45-residue segment of the prion-like low-complexity domain of the protein, whereas the remaining parts of the protein (275 residues) form a fuzzy coat around the fibril core. The fibril consists of two fibril protein stacks that are arranged into a pseudo-2₁ screw symmetry. The ordered core harbors several of the positions that are known to be affected by disease-associated mutations, but does not encompass the most aggregation-prone segments of the protein. These data indicate that the structures of amyloid fibrils from full-length proteins may be more complex than anticipated by current theories on protein misfolding.