Lysosomal thiol cathepsins and their endogenous inhibitors. Distribution and localization.
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Animals↗
Biomedical subjects
E Kominami
Publications and source records attributed to E Kominami.
Three forms of thiol proteinase inhibitor from rat liver formed depending on the oxidation-reduction state of a sulfhydryl group.
Three forms of a thiol proteinase inhibitor were isolated from rat liver cytosol. The monomeric inhibitor (pI 5.2) (TPI-1) formed a complex with cathepsin H even in the absence of reducing agents. The inhibitor with pI 5.0 (TPI-2) was inactive in the absence of reducing agents but was converted to an active inhibitor on addition of reducing agents such as dithiothreitol, GSH, cysteine, or 2-mercaptoethanol. The dimeric inhibitor (TPI-D) with an intermolecular disulfide bridge was also inactive and was converted to the active monomeric inhibitor on addition of dithiothreitol. TPI-2 is most likely a mixed disulfide with glutathione. One (Cys-3) of two cysteine residues exposed on the surface of the molecule of TPI-2 is involved in the formation of a mixed disulfide, and the other cysteine residue (Cys-64) is buried in the molecule. The activity of rat liver thiol proteinase inhibitor may possibly be regulated by formation of a protein mixed disulfide or by reduction of the mixed disulfide.
Amino Acids↗
Studies on thiol proteinase inhibitors in rat peripheral blood cells.
The concentrations of two types of endogenous thiol proteinase inhibitors, TPI-alpha and TPI-beta, in rat peripheral blood cells were determined by sensitive immunoassay methods. The concentration of TPI-alpha was highest in neutrophils among the peripheral blood cells tested. On the contrary, the concentration of TPI-beta was highest in macrophages followed in order by neutrophils, lymphocytes and erythrocytes. The serum level of TPI-beta was 47 times that of TPI-alpha. Immunohistochemical studies showed that in rat liver, TPI-beta was localized in Kupfer cells, and that only little TPI-alpha was present in liver tissue.
Animals↗
Amino acid sequence of rat epidermal thiol proteinase inhibitor.
The complete amino acid sequence of rat epidermal thiol proteinase inhibitor was determined. The unique 103-residue sequence was derived by analysis of two peptides generated by limited proteolysis of the native inhibitor with Staphylococcus aureus V8 protease and of three cyanogen bromide fragments. The protein has a high degree of sequence homology to either rat liver or human leucocyte inhibitor but is not identical and may represent a new type of low molecular weight thiol proteinase inhibitors.
Amino Acid Sequence↗
Gyrate atrophy of the choroid and retina: decreased ornithine aminotransferase concentration in cultured skin fibroblasts from patients.
A sensitive and convenient radioisotopic assay for ornithine aminotransferase (OAT) and an enzyme immunoassay for human ornithine aminotransferase were developed for studying decrease in activity of this enzyme in gyrate atrophy of the choroid and retina with hyperornithinemia. Picogram amounts of human OAT could be detected by the enzyme immunoassay. The OAT activity in cultured fibroblasts from two patients was 6% and 2% of that in control fibroblasts, and did not increase on addition of a high concentration of vitamin B6. The decreased activity, assayed by enzyme immunoassay, was associated with decreased enzyme concentration, suggesting that deficiency of OAT in these patients is not due to production of a structurally altered enzyme lacking catalytic activity, but to decreased production of enzyme protein. When cells from patients were repeatedly subcultured, selective loss of both the activity and concentration of OAT was observed, without changes in activities of several other enzymes tested.
Atrophy↗
Degradation of myelin proteins by cathepsin B and inhibition by E-64 analogue.
Purified human brain myelin was isolated, heat-treated to inactivate the endogenous proteolytic activity and incubated with cathepsin B purified from rat liver, at pH 6.0. Incubation resulted in a marked reduction of myelin basic protein (BP) and partial breakdown of proteolipid protein or Wolfgram protein. Degradation of myelin proteins was inhibited by E-64 analogue (E-64-a). E-64 is a specific thiol protease inhibitor isolated from a solid culture of Aspergillus japonicus. The present study suggests that cathepsin B may play some role in demyelination.
Cathepsin B↗
Mechanism of postmortem autolysis of skeletal muscle.
Male Wistar rats were treated with the carboxyl, thiol, and serine protease inhibitors, pepstatin, Ep-475[L-trans-epoxysuccinyl-leucylamide(3-methyl) butane; E-64-c], and chymostatin. Then the femoral muscles of these rats and control animals were used for preparation of myofibril proteins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to analyze the degradation of these myofibril proteins with time (day) after death. The protease activities of the muscle were also measured. Tropomyosin was degraded most rapidly, followed by the heavy chain of myosin, alpha-actinin, and light chains of myosin (L1 and L2). Actin and troponin-T were degraded slowly, still remaining unchanged 2 weeks after death. The degradation of protein was not inhibited by pepstatin but was inhibited strongly by Ep-475 and very strongly by chymostatin. Chymostatin inhibited degradation of all components except alpha-actinin more strongly than Ep-475. Data on enzyme activities were consistent with these findings. These results suggest that after death the components of myofibrils are degraded with various proteases at various rates depending on their properties or their structure and that the proteases involved in the degradation show some specificity.
Animals↗
Different tissue distributions of two types of thiol proteinase inhibitors from rat liver and epidermis.
The concentrations of two types of endogenous inhibitors of thiol proteinases were determined in soluble extracts of various rat tissues by means of a sensitive enzyme immunoassay method, which consisted of solid-phase immobilized anti-rat liver inhibitor or anti-rat epidermal inhibitor and antibodies labeled with horseradish peroxidase. The minimum detectable amounts of inhibitors from liver and epidermis were 30 pg and 3 pg/assay, respectively. The tissue distributions of the epidermal and liver-type inhibitors were found to differ. The liver-type inhibitor was found to be widely distributed in various tissues at levels of 76-420 ng/mg protein, whereas the epidermal-type inhibitor was found at high levels in the skin, tongue, esophagus, stomach, intestine, and vagina, but at quite low levels in other tissues tested.
Animals↗
Increases in cathepsins B and L and thiol proteinase inhibitor in muscle of dystrophic hamsters. Their localization in invading phagocytes.
In dystrophic hamsters, increases in the levels of cathepsin B plus L and thiol proteinase inhibitor were marked in skeletal muscle, but only slight in heart muscle. The lysosomal hydrolases did not increase in parallel in dystrophic muscle: cathepsin B plus L and beta-glucuronidase increased, but cathepsin C and acid phosphatase did not. In immunohistochemical studies with antibodies against rat liver cathepsin B and thiol proteinase inhibitor, the proteinase and inhibitor were both stained in phagocytes, chiefly macrophages, but not in muscle cells, indicating that the increases in cathepsin B plus L and thiol proteinase inhibitor in dystrophic muscle are due to their presence in invading phagocytes. The levels of cathepsin B plus L, beta-glucuronidase and thiol proteinase inhibitor in isolated peritoneal macrophages were 50 to 180 times higher than those in skeletal muscle, but the levels of acid phosphatase and cathepsin C were only about 10 to 30 times those in skeletal muscle. Plots of the cathepsin B plus L activities versus the level of thiol proteinase inhibitor in homogenates of tissues of various animals showed an exponential rather than a linear relation between the two activities, suggesting that the syntheses of the proteinases are higher than that of the inhibitor in phagocytes invading dystrophic muscle.
Animals↗
Amino acid sequence of rat liver thiol proteinase inhibitor.
The complete amino acid sequence of rat liver thiol proteinase inhibitor is presented. Its unique 98 residue sequence was derived mostly from analyses of a limited proteolysis product generated during the isolation of the protein with an active papain affinity column and of fragments produced by cleavage at arginyl bonds. The intact protein prepared with a tetrathionate inactivated ficin column has a unique amino-terminal sequence (Ac-Met-Met-Cys-). The inhibitor has no sequence homology with any proteinase inhibitor of known structure.
Amino Acid Sequence↗
Sequestration of cytoplasmic enzymes in an autophagic vacuole-lysosomal system induced by injection of leupeptin.
Administration of leupeptin to rats induces the accumulation of numerous autophagic vacuoles in the liver. Furuno et al. (Furuno, K., Ishikawa, T., and Kato, K. (1982) J. Biochem. (Tokyo) 91, 1485-1494) have recently devised a method for Percoll density gradient equilibrium fractionation of crude lysosomal fractions to isolate a highly enriched preparation of autophagic vacuoles. This system was used to determine whether cytoplasmic enzymes are normally sequestered into autophagic vacuoles in fed animals. Within 30 min following the administration of leupeptin to fed rats, several cytoplasmic enzymes could be demonstrated in vacuolar fractions heavier than mitochondria and normal lyosomes. The activities of tyrosine aminotransferase and lactic dehydrogenase as well as antigens of fructose-bisphosphate aldolase were detectable in fractions with densities of 1.115 to 1.15 g/ml containing cathepsins and acid phosphatase. The cytoplasmic enzymes in these fractions exhibited latency and were sequestered within membranous organelles. Six hours after the administration of leupeptin, the autophagic vacuoles gradually disappeared from these fractions concurrently with the loss of both cytoplasmic and lysosomal marker enzymes. For 6 h after injection of leupeptin the activities of cathepsin D and acid phosphatase increased in autophagic vacuoles and decreased in the postvacuolar lysosomal fraction. Administration of dexamethasone, which induces the synthesis of tyrosine aminotransferase and cytosolic aspartate aminotransferase, selectively increased the sequestration of these enzymes to proportional degrees. Cycloheximide administered simultaneously with leupeptin rapidly inhibited formation of autophagic vacuoles and the sequestrations of both cytoplasmic and lysosomal enzymes. However, when cycloheximide was administered 1 h after leupeptin, the formation of autophagosomes and the sequestration of cytoplasmic enzymes were inhibited but the vacuolar uptake of acid phosphatase and cathepsin D continued to increase for several hours. When cycloheximide was injected 1 h after leupeptin, losses of lactic dehydrogenase and aldolase proteins were observed in autophagic vacuoles isolated 1 and 2 h later.
Acid Phosphatase↗
Structures and functions of lysosomal thiol proteinases and their endogenous inhibitor.
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Amino Acid Sequence↗
Transformation of leukotriene D4 catalyzed by lysosomal cathepsin H of rat liver.
Among several intracellular protease tested, cathepsin H transformed leukotriene D4 to E4 with a release of glycine in a stoichiometric quantity. Under the optimal conditions the rate of leukotriene D4 transformation by cathepsin H was about 3% of the hydrolysis rate of alpha-N-benzoyl-DL-arginine-2-naphthylamide which is commonly utilized as a very efficient substrate to test the peptidase activity of the enzyme. Leukotriene C4 was not transformed to leukotriene D4 by cathepsin H. Neither cathepsin B nor C was active with leukotrienes C4 and D4.
Animals↗
A new sensitive and convenient assay of ornithine aminotransferase.
A new radioisotopic assay for ornithine aminotransferase with [U-14C]ornithine as a substrate was developed. The dihydroquinazolinium compound formed was extracted from the reaction mixture with n-butanol and an addition of high concentration of sodium sulfate. This assay is sensitive and convenient and more than 50 assays can be done in one day without any special apparatus. The activities of ornithine aminotransferase in rat liver and human lymphoblastoid cells could be measured at nanomole levels by this method. Thus, the assay should be useful for measurement of OAT activity in cultured cells and for studies on the metabolic bases of the different types of ornithine aminotransferase deficiency: vitamin B6-responsive and -nonresponsive types.
Animals↗
Purification and characterization of thiol proteinase inhibitor from rat liver.
A thiol proteinase inhibitor was purified from rat liver by essentially the same procedure as reported previously (Kominami, E., Wakamatsu, N., and Katunuma, N. (1981) Biochem. Biophys. Res. Commun. 99, 568-575), but without heat treatment. The purified inhibitor appears homogeneous on polyacrylamide gel electrophoresis with and without sodium dodecyl sulfate and displayed no multiple forms. The inhibitor has Mr = 12,500 and contains 50.5% of polar amino acid residues, 9.3% aromatic amino acids, and no tryptophan. The presence of 2 half-cystines/molecule and the absence of free thiol groups indicate that the inhibitor possesses one disulfide bridges. The inhibitor inhibits cathepsin H by forming an enzyme-inhibitor complex in a molar ratio of 1:1. It inhibits most thiol proteinases such as cathepsin H, L, B, and C, papain, and ficin, but not calcium-activated neutral proteinase or serine proteinases or carboxyl proteinases. The inhibitor was found in various rat tissues. Immunological diffusion analysis with anti-liver thiol proteinase inhibitor serum indicated that the rat liver inhibitor is immunologically identical with the inhibitors from other rat tissues. On subcellular fractionation of rat liver, the thiol proteinase inhibitor was recovered in the cytosol fraction.
Amino Acids↗
Comparison of properties of thiol proteinase inhibitors from rat serum and liver.
Thiol proteinase inhibitors in rat serum were purified and their properties were compared with those of rat liver thiol proteinase inhibitor. The inhibitors in rat serum were separated into three forms (S-1, S-2, and S-3) by linear gradient elution from a DE52 column. One inhibitor (S1) was purified to homogeneity by chromatography on ficin-bound Sepharose and Sephadex G-150 columns. The apparent molecular weights of S1, S2, and S3 on Sephadex G-150 columns were 90,000, 95,000, and 160,000, respectively. Serum thiol proteinase inhibitor and liver thiol proteinase differed in the following: 1) all three forms of serum inhibitor had much higher molecular weights than the liver thiol proteinase inhibitor (Mr = 12,500); 2) no cross-reactivity was observed between serum inhibitors and liver inhibitor in tests with either antiserum inhibitor or anti-liver antiserum; 3) both serum inhibitor and liver inhibitor were specific for thiol proteinases, but had different inhibition spectra; 4) the liver inhibitor did not bind to concanavalin A-Sepharose, whereas the serum inhibitor bound and was eluted with alpha-methyl mannoside. A thiol proteinase inhibitor of high molecular weight detected in tissue homogenates inhibited papain markedly but did not inhibit cathepsin H. Its activity was diminished by perfusion of the organ, indicating that it is derived from serum.
Animals↗
Modification of rat liver fructose biphosphate aldolase by lysosomal proteinases.
In vivo proteolytic modification of liver aldolase on administration of leupeptin, a thiol proteinase inhibitor of microbial origin, is reported. When leupeptin was injected into rats, the activity of aldolase in the liver decreased to 40% of that in control rats. Molecular properties of aldolase isolated from the livers of control rats and leupeptin-treated rats indicated that a decrease of aldolase activity is attributable to hydrolysis of a peptide linkage(s) near the carboxyterminal of the enzyme. Injection of leupeptin also caused marked increase in the activities of free lysosomal proteinases, such as cathepsin A and cathepsin D and moderate increase of cathepsin B and cathepsin L. Increase in free activity of cathepsin A returned to the level of control rats by 12 hr after injection of leupeptin, whereas 36 hr was required for recovery of decreased aldolase activity. When insulin was coinjected with leupeptin, increase in the activity of free cathepsin A and decrease of activity of aldolase produced by the injection of leupeptin was prevented. These findings indicate that modification of aldolase may be due to action of a lysosomal protease(s). Incubation of the purified aldolase with the lysosomal fraction produced the same changes in properties of aldolase as those observed in vivo on injection of leupeptin. The aldolase inactivating proteinase in the lysosomal fraction was inhibited by PMSF and leupeptin and not by pepstatin. Purified cathepsin A (a serine proteinase), cathepsin B and cathepsin L (thiol proteinase) are potent inactivators of aldolase but cathepsin H and cathepsin D are not. Cathepsin A, B and L are involved in inactivation of aldolase in lysosomes. Endogenous thiol proteinase inhibitor which inhibits lysosomal thiol proteinases (cathepsin B, L and H) is found in the cytosol fraction of liver. The level of thiol proteinase inhibitor actually decreased to 60% of that in control rats in leupeptin-treated rats, suggesting that non-thiol proteinase cathepsin A is a major factor in inactivation of aldolase in lysosomes. Not only leupeptin but also other proteinase inhibitors (antipain, E-64-D, chloroquine) caused increase of labilization of the lysosomes and decrease in aldolase activity. Physiological stimuli which are known to induce the labilization of the lysosomal membrane, such as starvation and glucagon, caused slight or no significant increase of activities of free cathepsin A and D and resulted in no apparent change in aldolase activity.
Animals↗
Immunological studies on cathepsins B and H from rat liver.
The immunological properties of thiol proteinases from rat liver, cathepsin B, H, and L, were examined. Rabbit antisera were prepared against cathepsins B and H from rat liver. Anti-cathepsin B and H ser quantitatively precipitated only the corresponding enzyme protein. On immunodiffusion analysis, anti-cathepsin B serum reacted with cathepsin B, but not with cathepsin H, indicating that the three thiol proteinases are distinct. Immunoelectrophoresis using a mixture of anti-cathepsin B and anti-cathepsin H showed that the precipitin line with cathepsin B moved faster to the anode than with cathepsin H. Immunological diffusion with antisera indicated that rat liver cathepsin B and H were immunologically identical with cathepsins B and H from rat kidney, lung, spleen, brain, and heart, but different from cathepsin B or H from human or rabbit liver.
Animals↗