A 33.5-kDa heat- and protease-resistant NADH oxidase inhibited by capsaicin from sera of cancer patients

Sera from patients with a variety of cancers, including solid carcinomas, leukemias, and lymphomas, contain a ca. 33.5-kDa protein absent from sera of healthy volunteers or patients not diagnosed as having cancer. The protein exhibits an NADH oxidase activity inhibited by 8-methyl-N-vanillyl-6-noneamide (capsaicin). The activity and the protein are resistant to digestion by proteases (trypsin, chymotrypsin, proteinase K, subtilisin) and to heat. Following protease digestion to reduce the content of major serum proteins, the 33.5-kDa protein could be detected on Western blots of SDS-PAGE transferred to nitrocellulose membranes using polyclonal antisera to a corresponding partially purified 33.5-kDa protein shed into culture media conditioned by growth of HeLa cells. No corresponding protein was seen with control sera. The findings confirm the capsaicin-inhibited NADH oxidase activity of cancer sera as a circulating marker potentially specific to sera of cancer patients and identify a ca. 33.5-kDa protein resistant to proteases and heat as the source of the circulating capsaicin-inhibited NADH oxidase activity.

A circulating form of NADH oxidase activity responsive to the antitumor sulfonylurea N-4-(methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984) specific to sera from cancer patients

Our laboratory has described a drug-responsive NADH oxidase activity of the external surface of the plasma membrane of HeLa and other cancer cells, but not from normal cells, that was shed into media conditioned by the growth of cancer cells such as HeLa. The shed form of the activity exhibited the same drug responsiveness as the plasma membrane-associated form. In this study, sera from tumor-bearing and control rats, cancer patients, normal volunteers, and patients with diseases other than cancer were collected and assayed for a cancer-specific form of NADH oxidase responsive to the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). With sera from tumor-bearing rats and cancer patients, LY181984 added at a final concentration of 1 microM either inhibited or stimulated the activity. With sera from control rats, normal volunteers, or patients with disorders other than cancer, the drug was without effect on the NADH oxidase activity of the sera. The activity altered by the antitumor sulfonylurea was present both in freshly collected sera and in sera stored frozen. Inhibition was half maximal at about 30 nM LY181984. The sulfonylurea-altered activity was found in sera of nearly 200 cancer patients including patients with solid cancers (e.g., breast, prostate, lung, ovarian) and with leukemias and lymphomas. We postulate that the serum presence of the antitumor sulfonylurea-responsive NADH oxidase represents an origin due to shedding from the patient's cancer. If so, the antitumor-responsive NADH oxidase would represent the first reported cell surface change universally associated with all forms of human cancer.

Identification, purification, and characterization of a PA700-dependent activator of the proteasome

The activity of the intracellular protease, the proteasome, is modulated by a number of specific regulatory proteins. One such regulator, PA700, is a 700,000-Da multisubunit protein that activates hydrolytic activities of the proteasome via a mechanism that involves the ATP-dependent formation of a proteasome-PA700 complex. Four subunits of PA700 have been shown previously to be members of a protein family that contains a consensus sequence for ATP binding, and purified PA700 expresses ATPase activity. We report here the identification, purification, and initial characterization of a new modulator of the proteasome. The modulator has no direct effect on the activity of the proteasome, but enhances PA700 activation of the proteasome by up to 8-fold. This activation is associated with the formation of a proteasome/PA700-containing complex that is significantly larger than that formed in its absence. The modulator has a native Mr of approximately 300,000, as determined by gel filtration chromatography, and is composed of three electrophoretically distinct subunits with Mr values of 50,000, 42,000, and 27,000 (p50, p42, and p27, respectively). Amino acid sequence analysis of the subunits shows that p50 and p42 are members of the same ATP-binding protein family found in PA700. The p50 subunit is identical to TBP1, a protein previously reported to interact with human immunodeficiency virus Tat protein (Nelbock, P., Dillion, P. J., Perkins, A., and Rosen, C. A. (1990) Science 248, 1650-1653), while the p42 subunit seems to be a new member of the family. The p27 subunit has no significant sequence similarity to any previously described protein. Both p50 and p42, but not p27, were also identified as components of PA700, increasing the number of ATP-binding protein family members in this complex to six. Thus, p50 and p42 are subunits common to two protein complexes that regulate the proteasome. The PA700-dependent proteasome activator represents a new member of a growing list of proteins that regulate proteasome activity.

Identification and purification of a 90-kDa membrane-bound endogenous inhibitor of multicatalytic proteinase from human erythrocytes

We have identified and purified an endogenous inhibitor of multicatalytic proteinase (MCP) from human erythrocyte membranes. The inhibitor showed a molecular mass of 90 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The inhibitor protein was purified from the erythrocyte membranes using Heparinagarose and hydroxylapatite chromatography and the size exclusion on a Biogel A 1.5 m column in the presence of high salt. The 90-kDa protein inhibited all three peptidase activities of MCP; trypsin-like, chymotrypsin-like and peptidyl glutamyl peptide hydrolyzing (PGPH). However, it failed to cause any significant inhibition of caseinolytic activity of MCP, suggesting that the regulation of proteinase and peptidase activities is distinct. The inhibition of the chymotrypsin-like activity was noncompetitive. The results suggest that the 90-kDa inhibitor protein may be an important regulator of membrane-bound MCP.

Multienzyme control serum (Seraclear-HE) containing human enzymes from established cell lines and other sources. 2: Evaluation as candidate working enzyme Reference Material for alanine and aspartate aminotransferases

Seraclear-HE, containing seven enzyme analytes from human sources, was evaluated as an intermethod calibrator for aspartate aminotransferase (AST) and alanine aminotransferase (ALT) to transfer Reference Method values to seven routine methods, including one based on hydrogen peroxide detection for possible unification of values (interlaboratory comparability of data). The commutabilities of AST from erythrocytes and ALT from a hepatoma cell line were studied between the consensus methods of Japan Society of Clinical Chemistry (chosen as the Reference Methods) and each of the automated routine methods at reaction temperatures of 30 degrees C and 37 degrees C. For AST, calibration of patients' sera with Seraclear-HE decreased average intermethod variation (CV) from 12% to 2%; for ALT, the decrease was from 20% to 3%. For both enzymes, Seraclear-HE was judged to be commutable between the Reference Methods and each of the methods investigated. The limitations for such use are discussed.

Multienzyme control serum (Seraclear-HE) containing human enzymes from established cell lines and other sources. 1: Preparation and properties

We have developed a new multienzyme control serum, Seraclear-HE, which was designed to function not only as an accuracy and precision control serum but also as an intermethod calibrator for unifying interlaboratory clinical enzyme data in terms of reference method values. Seraclear-HE contains as analytes the following enzymes of human origin only: aspartate aminotransferase (AST, EC 2.6.1.1) and lactate dehydrogenase (LD, EC 1.1.1.27) from erythrocytes; alanine aminotransferase (ALT, EC 2.6.1.2) from a hepatoma cell line; alkaline phosphatase (ALP, EC 3.1.3.1) from an amnion cell line; creatine kinase (CK, EC 2.7.3.2) from an embryo kidney cell line; gamma-glutamyltransferase (GGT, EC 2.3.2.2) from a macrophage cell line; and amylase (AMY, EC 3.2.1.1) from urine and saliva. The seven partly purified enzymes were lyophilized in partially delipidated human serum containing sucrose (50 g/L), pyridoxal 5'-phosphate (30 mmol/L), and other stabilizers. The material is stable for at least 2 years at temperatures < or = 10 degrees C. For two concentrations of this preparation, reference method values (mainly International Federation of Clinical Chemistry and Japan Society of Clinical Chemistry) obtained at both 30 degrees C and 37 degrees C are assigned.

Carbidopa/levodopa and selegiline do not affect platelet mitochondrial function in early parkinsonism

Previous studies have demonstrated impaired complex I activity in platelets from Parkinson's disease (PD) patients who were receiving levodopa and other medications for their disease. Eleven patients with early PD underwent three sequential plateletphereses: while on no medication, after receiving carbidopa/levodopa for 1 month, and after receiving carbidopa/levodopa plus selegiline for 1 additional month. As expected, carbidopa/levodopa and selegiline significantly improved motor function in these patients. Treatment with carbidopa/levodopa alone and carbidopa/levodopa plus selegiline did not affect the activities of complexes I, II/III, and IV and citrate synthetase. These observations support the hypothesis that impaired complex I activity in PD patients is a characteristic of the disease and not due to medications.

Isolation of a complex of respiratory burst oxidase components from resting neutrophil cytosol

The respiratory burst oxidase of neutrophils is a multicomponent enzyme, dormant in resting cells, that catalyzes the reduction of oxygen to O2- at the expense of NADPH. In the resting neutrophil, some of the components of the oxidase, including proteins p47phox and p67phox, are in the cytosol, while the rest are in a fraction that usually copurifies with plasma membrane. Recent evidence has suggested that at least some of the cytosolic oxidase components exist as a complex. We have now purified such a complex from the cytoplasm of resting neutrophils using an affinity column prepared with an antibody that recognizes the C-terminal decapeptide of p47phox. Immunoblotting showed that the complex contained both p47phox and p67phox. When supplemented with recombinant p67phox, the complex displayed considerable activity in a cell-free oxidase-activating system, and even without added p67phox, the complex could more than double O2- production in an oxidase-activating system supplemented with suboptimal amounts of cytosol. Isolation of the complex was blocked by preincubating the affinity column with CFSTKRKLASAV, the peptide against which the antibody was raised. On gel filtration, the complex migrated with a molecular weight of 240-300K, similar to that observed with whole neutrophil cytosol. The p47phox/p67phox ratio in the gel-filtered complex was approximately 1 to 1. These results indicate that in resting neutrophil cytosol, p47phox and p67phox exist as a complex.

Identification, purification, and characterization of a high molecular weight, ATP-dependent activator (PA700) of the 20 S proteasome

In order to identify protein complexes consisting of the proteasome and specific proteasome regulators, crude soluble lysates of red blood cells were fractionated by gel filtration chromatography and by velocity sedimentation centrifugation. The fractionated lysates were then tested for the relative distribution of proteasome activity, proteasome protein, and protein of a known proteasome activator, PA28. At least two proteasome complexes containing PA28 were identified. One of these complexes had an apparent molecular weight of approximately 1,750,000, and appeared to have much more proteasome activity than could be accounted for by its relative concentrations of proteasome and PA28 protein. We hypothesized that this complex contained another activator of the proteasome, and we sought to purify this activator from extracts of red blood cells. A proteasome activator with an apparent molecular weight of approximately 700,000 was identified, purified, and characterized. This activator, termed PA700, greatly stimulated the peptidase activities of the proteasome in an ATP-dependent fashion. PA700 was composed of about 16 polypeptides ranging in molecular weight from 20,000 to 100,000. The ATP-dependent activation of the proteasome by PA700 was closely linked to the formation of a high molecular weight complex that required no additional ATP for activated proteolysis. These results indicate that PA700 is a regulatory protein of the proteasome and is a component of at least one high molecular weight proteasome-containing complex occurring in cell extracts.

Activation factors of neutrophil NADPH oxidase complex

Professional phagocytes, neutrophils, possess a unique membrane-associated NADPH oxidase system, dormant in resting cells, which becomes activated upon exposure to the appropriate stimuli and catalyzes the one-electron reduction of molecular oxygen to superoxide, O2-. Oxidase activation involves the assembly, in the plasma membrane, of membrane-bound and cytosolic constituents of the oxidase system, which are disassembled in the resting state. The oxidase system consists of two plasma membrane-bound components; low-potential cytochrome b558, which is composed of two subunits of 22 kDa and 91 kDa, and a flavoprotein related to the electron transport between NADPH and heme-binding domains of the oxidase. Recent reports have indicated that FAD-binding sites of the oxidase are contained in cytochrome b558 (flavocytochrome b558). At least two cytosolic components, 67 kDa protein and a phosphorylated 47 kDa protein, are known to translocate to the plasma membrane, ensuring assembly of an active O2(-)-generating NADPH oxidase system. More recently, the membrane (Raps) and cytosolic (Racs) GTP-binding proteins have been established as essential to oxidase assembly. It is the purpose of this review to focus on recent data concerning the regulatory mechanisms which lead to organization and activation of the neutrophil NADPH oxidase system.

PA28, an activator of the 20 S proteasome, is inactivated by proteolytic modification at its carboxyl terminus

PA28, a protein activator of the 20 S proteasome, was previously identified in soluble extracts of bovine red blood cells (Ma, C.-P., Slaughter, C. A., and DeMartino, G. N. (1992) J. Biol. Chem. 267, 10515-10523). To determine whether this regulatory protein is as widely distributed as the proteasome, PA28 content and activity were examined in various eukaryotic tissues by immunoblot analysis and by functional assays of tissue extracts. PA28 protein was present in all sources examined. PA28 activity, however, was not detected in many of these sources, including those with the highest level of PA28 protein. To determine the biochemical basis of this result, PA28 was purified from extracts of rat liver, which had high levels of PA28 protein but no PA28 activity. The resulting purified PA28 had no detectable activity but had native and subunit molecular weights indistinguishable from the active PA28 of bovine red blood cells. Using the inactivation of purified PA28 as an assay, a protein that inactivated PA28 without altering its apparent molecular weight on SDS-polyacrylamide gel electrophoresis was identified, purified, and characterized from bovine liver. It had biochemical and catalytic characteristics similar to those of lysosomal carboxypeptidase B. When leupeptin, an inhibitor of lysosomal carboxypeptidase B, was included in the buffers used for the preparation of PA28, PA28 activity was detected in tissues which otherwise failed to demonstrate this activity. A similar result was obtained when extracts were prepared in a manner that minimized disruption of lysosomes. Other carboxypeptidases such as carboxypeptidase Y and pancreatic carboxypeptidase B also inactivated PA28 without altering its apparent molecular weight. Active PA28 binds to the proteasome to form a protease-activator complex that can be isolated after velocity sedimentation centrifugation through glycerol density gradients. Carboxypeptidase-inactivated PA28 failed to form such a complex, suggesting that the carboxyl terminus of PA28 is required for binding to the proteasome. These results indicate the importance of the carboxyl terminus of PA28 for proteasome activation.

Purification and characterization of endogenous protein activator of human platelet proteasome

An endogenous activator of 20S proteasome was purified from human platelets and its effect on three peptidase activities of proteasome was studied. This activator had a molecular weight of 170 kDa, and was composed of 32 kDa polypeptides as determined by SDS-PAGE. It was highly labile upon heat treatment (56 degrees C, 20 s) and proteinase (pronase CB) digestion. Suc-LLVY-MCA degrading activity of the platelet proteasome showed positive cooperativity between two or more catalytic sites because the coefficient was 1.54 when analyzed by use of the Hill plot. The endogenous activator increased Vmax and caused a loss of cooperativity. The plot of reaction velocity as a function of activator concentration yielded a saturation curve, implying the binding of the activator to proteasome. Boc-LTR-MCA degrading activity followed Michaelis-Menten kinetics. The activator enhanced the activity by increasing Vmax and decreasing Km. In contrast, CBz-LLE-2NA degrading activity could not be analyzed according to any kinetic scheme reported so far. The activator stimulated this activity at lower substrate concentrations (below 200 microM), while it inhibited the activity at higher substrate concentrations (400-800 microM). It is concluded from these findings that the endogenous protein activator may regulate the intracellular proteasome activity by functioning as a positive allosteric effector.

Serum concentration and localization in tumor cells of proteasomes in patients with hematologic malignancy and their pathophysiologic significance

The pathophysiologic significance of proteasomes in hematologic malignancies was examined by comparison of the proteasome levels in normal subjects and patients with benign liver diseases. The serum proteasome level measured by enzyme-linked immunosorbent assay was found to be positively correlated with the tumor burden of the patients with hematologic malignancies such as acute leukemia, chronic myelogenous leukemia, non-Hodgkin's lymphoma, and myeloma. Immunohistochemical staining showed that proteasomes were strongly expressed in these tumor cells, especially in the nuclei. These data suggest that the elevated levels of serum proteasomes in these patients are derived from tumor cells, reflect the tumor burden, and so provide prognostic information. However, in patients with benign liver diseases, serum proteasome levels correlated with serum alanine aminotransferase activities, suggesting that in hematologic malignancies associated with liver injury some of the serum proteasomes may originate from hepatocytes. The marked production of proteasomes by malignant blood cells may be involved in transformation and proliferation of these cells.

Identification and localization of a cysteinyl residue critical for the trypsin-like catalytic activity of the proteasome

Chemical modification of the proteasome with N-ethylmaleimide (NEM) was performed for the purpose of identifying amino acid residues that play a role in the enzyme's proteolytic function. Modification of the proteasome with NEM specifically and irreversibly suppressed one of the three peptidase activities of the enzyme, viz., the "trypsin-like" activity. Leupeptin, a reversible competitive inhibitor of this activity, protected the activity from NEM inactivation, suggesting that NEM modifies a residue in the leupeptin binding site. Comparisons of enzyme samples labeled with [14C]NEM either in the presence or in the absence of leupeptin allowed the identification of a proteasome subunit containing an NEM-modified, leupeptin-protected cysteinyl residue. The leupeptin protection experiments suggest that residues of this subunit contribute to the active site responsible for the proteasome's trypsin-like activity. This subunit was purified by reverse-phase high-performance liquid chromatography. Peptide mapping and N-terminal amino acid sequencing were employed to acquire information about the primary structure of the subunit, including the sequence surrounding the leupeptin-protected cysteinyl residue. The sequencing data suggest that this proteasome subunit is evolutionarily related to other proteasome subunits that have been sequenced, which show no homology to other known proteases. The assignment of a catalytic function to a member of the proteasome family supports the hypothesis that proteasome subunits represent a structurally and possibly mechanistically novel group of proteases.

Human erythrocyte contains a factor that stimulates the peptidase activities of multicatalytic proteinase complex

A novel biological factor that stimulates the peptidase activities of multicatalytic proteinase complex (MPC) has been identified and partially purified from human erythrocytes. The stimulatory factor enhances trypsin-like, chymotrypsin-like and peptidyl-glutamyl peptide hydrolyzing activity of MPC in a dose related manner. At saturating concentration of the stimulatory factor, MPC increases the activity to a different extent (10 to 56 fold) depending on the substrate used to assay the enzyme. The stimulatory factor does not hydrolyze neither amino-blocked peptides which are used to assay MPC nor typical substrates for amino and diamino-peptidases. The stimulatory factor is characterized by a high molecular mass (300 kDa) and an extreme instability since it loses the activity at 46 degrees C in 10 min and at 4 degrees C within a week. The stimulatory activity is inactivated by incubation in acidic or alkaline media, and by treatment with protease V8, but it is relatively resistant to the action of trypsin. It has been suggested that the novel stimulatory factor herein described is a protein or a protein complex which may modulate the function and the activity of MPC by association-dissociation interaction.

Monitoring the response to injury

Tissue trauma leads to a severity-dependent activation of plasma and cellular systems. This response can be recorded by determining parameters which represent the activation state of these systems. In severely injured patients with multiple trauma three out of 14 parameters measured at the time of admission proved to be indicators of subsequent septic complications with a high degree of accuracy: Fibrinopeptide A (FPA--the first split product of fibrinogen), the C3 split product C3a, and the elastase-alpha 1 proteinase inhibitor-complex (E alpha 1 PI). In a second series of multiple-injured patients with femoral fractures who did not develop clinical sepsis (N = 25) these parameters were measured continuously to evaluate the influence of injury severity and of therapeutic strategy on the further course. We found a strong correlation between injury severity (ISS) and the degree of activation. The signs of activation decreased rapidly following immediate operative fixation, and remained elevated or even increased after primary femoral traction and secondary stabilization. The operative procedure did not cause any additional activation. Complications such as infection or the formation of haematomas were reflected by raised parameter levels.

Proteasome and its novel endogeneous activator in human platelets

Proteasome, a high molecular weight multicatalytic protease, was purified from the cytosolic fraction of human platelets for the first time. The biochemical properties of the enzyme including substrate specificity, optimal pH and effects of various inhibitors were almost identical with those of other cells. During the purification with a Heparin-Sepharose chromatography, a novel endogenous activator of the protease was identified and was partially purified. The activator enhanced both chymotrypsin or trypsin like activities of the proteasome in a dose related manner and was inactivated by heating at 56 degrees C for 30 min. This newly identified activator may serve as an important regulator or cofactor of intracellular activities of the proteasome.

Multicatalytic and 26 S ubiquitin/ATP-stimulated proteases in maturing rabbit red blood cells

Rabbit red blood cells of various ages were separated on Percoll gradients and the activities of two large cytosolic proteases were measured. Both the multicatalytic protease (MCP), assayed by hydrolysis of fluorigenic peptides, and the 26 S ubiquitin/ATP-stimulated protease, assayed by degradation of ubiquitin-lysozyme conjugates, declined 3-fold or less during maturation of rabbit reticulocytes to erythrocytes. The ability of MCP to hydrolyze three classes of peptides decreased in parallel indicating that the 20 S protease is not significantly remodeled during red blood cell maturation.

Human erythrocyte multicatalytic proteinase: activation and binding to sulfated galacto- and lactosylceramides

Chymotrypsin-like activity of multicatalytic proteinase (MCP) purified from human erythrocytes was selectively activated 2.5--3.5-fold by sulfated glycolipids such as galactosylceramide sulfate (SM4) and lactosylceramide sulfate (SM3) but not by other glycolipids including galactosylceramide (GalCer), lactosylceramide (LacCer), GD1a, GM1 and GM3. Heparin also selectively activated trypsin-like activity 2.5-fold, while other mucopolysaccharides did not. This proteinase molecule bound specifically and with high affinity to both SM4 and SM3, but not to GalCer, LacCer and GM3. The binding of SM4 and SM3 to the enzyme molecule was also confirmed by thin layer chromatography.

Regulation of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase expression and activity in the hypophysectomized rat ovary: interactions between the stimulatory effect of human chorionic gonadotropin and the luteolytic effect of prolactin

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyzes an obligatory step in the conversion of pregnenolone and other 5-ene-3 beta-hydroxysteroids into progesterone as well as precursors of all androgens and estrogens in the ovary. Since 3 beta-HSD is likely to be an important target for regulation by pituitary hormones, we have studied the effect of chronic treatment with LH (hCG), FSH, and PRL on ovarian 3 beta-HSD expression and activity in hypophysectomized adult female rats. Human CG (hCG) [10 IU, twice a day (bid)], ovine FSH (0.5 microgram, bid), and ovine PRL (1 mg, bid) were administered, singly or in combination, for a period of 10 days starting 15 days after hypophysectomy. In hypophysectomized rats, PRL exerted a potent inhibitory effect on all the parameters studied. In fact, PRL caused a 81% decrease in ovarian 3 beta-HSD mRNA content accompanied by a similar decrease in 3 beta-HSD activity and protein levels. In addition, ovarian weight decreased by 40% whereas serum progesterone fell dramatically from 1.92 nmol/liter to undetectable levels after treatment with PRL. Whereas hCG alone had only slight stimulatory effects on 3 beta-HSD mRNA, protein content and activity levels, treatment with the gonadotropin partially or completely reversed the potent inhibitory effects of oPRL on all the parameters measured. FSH, on the other hand, had no significant effect on 3 beta-HSD expression and activity. In situ hybridization experiments using the 35S-labeled rat ovary 3 beta-HSD cDNA probe show that the inhibitory effect of PRL is exerted primarily on luteal cell 3 beta-HSD expression and activity. On the other hand, it can be seen that hCG stimulates 3 beta-HSD mRNA accumulation in interstitial cells. The present data show that hCG and PRL exert potent and opposite cell-specific effects on ovarian 3 beta-HSD expression, activity, and content in the rat ovary. Moreover, the present study could suggest that female infertility associated with hyperprolactinemia in women could well be related, at least in part, to the potent inhibitory effect of PRL on ovarian 3 beta-HSD expression and activity.

Interaction of human erythrocyte multicatalytic proteinase with polycations

The multicatalytic proteinase from human erythrocytes (macropain, proteasome) is a large enzyme composed of at least six distinct subunits ranging in molecular masses from 20 to 30 kDa. As its name implies, this proteinase appears to contain multiple catalytic sites with differing specificities toward peptide substrates. Several polycationic substances, including polylysines, polyarginine, protamine and histone H1 markedly stimulated caseinolytic activity of the proteinase. Activation was instantaneous, and involved increasing the Vmax of the proteinase for casein. Prolonged preincubation with polylysine at 37 degrees C resulted in autolytic inactivation of the proteinase. The polylysine concentrations required for half-maximal activation or autolytic inactivation were the same. A 23 kDa subunit of the proteinase disappeared at the same rate as loss of catalytic activity, and with the same pH dependence and polylysine concentration dependence. These results suggest that polylysine perturbs the structure of the multicatalytic proteinase, resulting in increased catalytic activity toward substrates; and, with prolonged exposure, allowing autoproteolytic inactivation to occur. The 23 kDa subunit appeared to be required for expression of caseinolytic activity, and may therefore be a catalytic subunit of the complex having activity against casein.

The proteasome (multicatalytic protease) is a component of the 1500-kDa proteolytic complex which degrades ubiquitin-conjugated proteins

Mammalian cells contain two large proteolytic complexes, the 650-kDa proteasome (or multicatalytic protease) and the 1500-kDa (26 S) Ubiquitin-conjugate-degrading enzyme. Since the proteasome is also required for the ATP-dependent degradation of ubiquitinated proteins, we tested whether it may be a component of the larger complex. The proteasome normally is soluble in 38% ammonium sulfate. However, after preincubation of reticulocyte extracts with ATP, several proteasome activities appeared in the 38% ammonium sulfate pellet, including the ability to degrade hydrophobic peptides and 14C-casein. Also, following preincubation with ATP, the precipitable fraction could degrade 125I-lysozyme-ubiquitin (Ub) conjugates. The activities were not present after incubation without ATP or with a nonmetabolizable ATP analog. Nondenaturing gel electrophoresis indicated the ATP-dependent appearance of a new band which degraded proteasome substrates, and reacted with an anti-proteasome monoclonal antibody on Western blot. This new band appeared larger than the proteasome and migrated similarly to the larger Ub-conjugate-degrading complex. The formation of the larger complex required factor(s) present in the 38% ammonium sulfate pellet and either the 40-80% fraction or the purified proteasome from reticulocytes or muscle. After complex formation, hydrolysis of Ub-protein conjugates and also the non-ubiquitinated substrate, casein, was stimulated severalfold by ATP, but non-metabolizable ATP analogs had little or no effect. Thus, the proteasome corresponds to component CF-3 of Ganoth et al. (Ganoth, D., Leshinisky, E., Eytan, E., and Hershkov, A. (1989) J. Biol. Chem. 263 12412-12419) and undergoes an energy-dependent association with other factors to form the 1500-kDa, ATP-requiring proteolytic complex.

Purification of human erythrocyte proteolytic enzyme responsible for degradation of oxidant-damaged hemoglobin. Evidence for identifying as a member of the multicatalytic proteinase family

Exposure of human red cells to oxidants such as phenylhydrazine, 2,4-dimethylphenylhydrazine and 4-hydrazinobenzoic acid stimulates the proteolysis of hemoglobin as evidenced by the increase in the rate of the free alanine and acid soluble amino groups released. An enzyme responsible for proteolytic degradation of oxidized hemoglobin, was purified from cytosolic fraction of erythrocytes by a DEAE-batch procedure followed by gel-filtration and ion-exchange chromatography. The final enzyme preparation produces a single band in non-denaturing polyacrylamide gel electrophoresis, and eight different bands of 23-32 kDa when subjected to polyacrylamide gel electrophoresis under denaturing conditions. The native enzyme has a molecular mass of about 700 kDa as estimated by gel filtration. The enzyme, unable to hydrolyze native hemoglobin, cleaves phenylhydrazine-treated hemoglobin into small peptides without free amino acid release. In addition, the enzyme shows an endopeptidase activity towards synthetic peptides having a tyrosine or an arginine in the P1 position, whereas it does not hydrolyze shorter peptides and those with a proline in the P1 or P2 position. The proteolytic activity of the enzyme against oxidized hemoglobin is inhibited by chymostatin and p-chloromercuribenzoate, while it is stimulated by N-ethylmaleimide and epoxysuccinylleucylamido-(4-guanidino)butane (E-64). The peptidase activity assayed on succinyl-Leu-Leu-Val-Tyr-MCA is inhibited by chymostatin, hemin, N-ethylmaleimide and p-chloromercuribenzoate. The results obtained show that in human erythrocytes oxidized hemoglobin is cleaved into peptides by a high molecular mass proteinase identified as a member of the multicatalytic proteinase family. It is also suggested that the complete degradation of oxidized hemoglobin to free amino acids requires the involvement of a further proteolytic enzyme(s) which remain(s) to be identified.

Significant amount of multicatalytic proteinase identified on membrane from human erythrocyte

Multicatalytic proteinase (MCP) was solubilized from human erythrocyte membrane with 0.1% Triton X-100 and purified to homogeneity using a combination of DEAE-cellulose, hydroxylapatite, and Ultrogel AcA34 chromatographies. This membranous MCP had similar properties to MCP purified in parallel from the cytosol. Both MCPs had a molecular mass of 570 kDa, were composed of apparently nine subunits of 22-36 kDa and had trypsin- and chymotrypsin-like activities. These activities were latent and required heating for the induction. However, slight differences were observed in the effects of reagents (DFP, monoiodoacetic acid, Mg2+, and Ca2+) between membranous and cytosolic MCP. The amount of MCP identified on membranes was estimated to be three-quarters or one-half of that found in the cytosol based on its trypsin- or chymotrypsin-like activity, respectively.