A new principle of regulation of enzymic activity. Activation and regulation of human polymorphonuclear leukocyte collagenase via disulfide-thiol exchange as catalysed by the glutathione cycle in a peroxidase-coupled reaction to glucose metabolism

Myocardial Connective Tissue Alterations

There is a complex network of collagen throughout the heart. It is composed of a hierarchy of fibrils and fibers ranging from 10 nm to 2–3 microns in diameter. This network can be broken down by ischemia, adriamycin administration, or disulfide administration in laboratory animals. Following loss due to coronary artery ligation, the ischemic area begins bulging within 3 h. General loss of portions of the collagen matrix is induced by intravenous oxidizing glutathione, and results in marked diffuse ventricular dilatation. Generalized collagen loss in the ventricles, as induced by disulfide administration or adriamycin infusion, persists for 6 months at which time evidence of some replacement is visible, and evidence of diffuse fibrosis is present. In humans, cardiac dilatation occurs in a variety of disease states without overstretch of sarcomeres. This presumes rearrangement of the muscle bundles, which can only occur with marked alterations of the collagen matrix. Ventricular dilatation, associated with viral myocarditis or puerperal cardiomyopathy, may persist for months, suggesting the collagen loss, as with the experimental animals, takes many months to repair. The cardiac dilatation may ameliorate, or, in some patients, deteriorate into heart failure. The animal experiments with loss of the collagen matrix, ventricular dilatation, and failure to replace the matrix for many months provide an explanation for persistent cardiac dilatation in various human diseases.

Mixed results with mixed disulfides

A period of research with Helmut Sies in the 1980s is recalled. Our experiments aimed at an in-depth understanding of metabolic changes due to oxidative challenges under near-physiological conditions, i.e. perfused organs. A major focus were alterations of the glutathione and the NADPH/NADP(+) system by different kinds of oxidants, in particular formation of glutathione mixed disulfides with proteins. To analyze mixed disulfides, a test was adapted which is widely used until today. The observations in perfused rat livers let us believe that glutathione-6-phosphate dehydrogenase (G6PDH), i.a. might be activated by glutathionylation. Although we did not succeed to verify this hypothesis for the special case of G6PDH, the regulation of enzyme/protein activities by glutathionylation today is an accepted posttranslational mechanism in redox biology in general. Our early experimental approaches are discussed in the context of present knowledge.

Accelerated ageing experiments with crosslinked and conventional ultra-high molecular weight polyethylene (UHMW-PE) stabilised with alpha-tocopherol for total joint arthroplasty

Samples of untreated ultra-high molecular weight polyethylene (UHMW-PE), UHMW-PE sterilized with gamma-rays in nitrogen atmosphere (conventional UHMW-PE, widely used for articulating surfaces in endoprostheses) and UHMW-PE, which has been crosslinked by electron beam irradiation and annealed subsequently, were stabilized with alpha-tocopherol and aged in air at 120 degrees C as well as in 10% aqueous hydrogenperoxide with 0.04 mg/ml FeCl3 as catalyst at 50 degrees C. The oxidative degradation was monitored with the help of infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), solubility measurements and size exclusion chromatography (SEC) and were compared to unstabilized samples. When aged in air at 120 degrees C, the crosslinked UHMW-PE showed a slightly slower increase of the carbonyl (CO)-number (according to DIN 53383) in FTIR than conventional UHMW-PE. A stabilisation with 0.4% w/w alpha-tocopherol resulted in an increase of lifetime by a factor of approx. 40 for all samples. Ageing in 10% aqueous H2O2 at 50 degrees C yielded similar results for all three unstabilised samples. The addition of the natural antioxidant alpha-tocopherol led to a prolongation of lifetime by a factor of approx. 2.5. A linear loss of alpha-tocopherol was detected during ageing. An increase of crystallinity as well as lamella thickness during ageing was observed with the help of DSC. The two-phase structure of crosslinked UHMW-PE with two melting endotherms at 114 degrees C and 137 degrees C was replaced very quickly by a single melting point at 130 degrees C. This effect was delayed with the stabilized samples. In the solubility and SEC measurements, a severe molecular degradation and drop of molar mass of all materials could be observed after ageing in H2O2, leading to a complete destruction and, in case of crosslinked UHMW-PE, to a serious damage of the molecular network, respectively.

Activation of matrix metalloproteinases by peroxynitrite-induced protein S-glutathiolation via disulfide S-oxide formation

Oxidative stress may cause tissue injury through activation of the precursors of matrix metalloproteinase (proMMPs). In this study, we observed glutathione (GSH)-dependent proMMP activation induced by peroxynitrite, a potent oxidizing agent formed during inflammatory processes. Peroxynitrite strongly activated all three types of purified human proMMPs (proMMP-1, -8, and -9) in the presence of similar concentrations of GSH. Of the potential reaction products between peroxynitrite and GSH, only S-nitroglutathione (GSNO(2)) caused proMMP activation. Extensive S-glutathiolation of the proMMP protein occurred during activation of proMMP by peroxynitrite and GSH, as shown by radiolabeling studies with [(35)S]GSH or [(3)H]GSH. Evidence of appreciable S-glutathiolation persisted even after dithiothreitol and protein-denaturing treatment, however, suggesting that some S-glutathiolation did not occur through formation of simple mixed disulfide. Matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry indicated that not only peroxynitrite plus GSH but also synthetic GSNO(2) produced dithiothreitol-resistant S-glutathiolation of the synthetic peptide PRCGVPD, which is a well conserved Cys-containing sequence of the propeptide autoinhibitory domain of proMMPs. PRCGVPD S-glutathiolation is presumed to be formed through glutathione disulfide S-oxide (GS(O)SR), based on the m/z 1064. Our results illustrate a unique mechanism of oxidative proMMP activation and oxidative tissue injury during inflammation.

Thiol-based antioxidants

The thiol redox status of intracellular and extracellular compartments is critical in the determination of protein structure, regulation of enzyme activity, and control of transcription factor activity and binding. Thiol antioxidants act through a variety of mechanisms, including (1) as components of the general thiol/disulfide redox buffer, (2) as metal chelators, (3) as radical quenchers, (4) as substrates for specific redox reactions (GSH), and (5) as specific reductants of individual protein disulfate bonds (thioredoxin). The composition and redox status of the available thiols in a given compartment is highly variable and must play a part in determining the metabolic activity of each compartment. It is generally beneficial to increase the availability of specific antioxidants under conditions of oxidant stress. Cells have devised a number of mechanisms to promote increased intracellular levels of thiols such as GSH and thioredoxin in response to a wide variety of stresses. Exogenous thiols have been used successfully to increase cell and tissue thiol levels in cell cultures, in animal models, and in humans. Increased levels of GSH and other thiols have been associated with increased tolerance to oxidant stresses in all of these systems and in some cases, with disease prevention or treatment in humans. A wide variety of thiol-related compounds have been used for these purposes. These include thiols such as GSH and its derivatives, cysteine and NAC, dithiols such as lipoic acid, which is reduced to the thiol form intracellularly, and "prothiol" compounds such as OTC, which are enzymatically converted to free thiols within the cell. In choosing a thiol for a specific function (e.g., protection of lung from oxidant exposure or protection of organs from ischemia reperfusion injury), the global effects must also be considered. For example, large increases in free thiols in the circulation are associated with toxic effects. These effects may be the result of thiyl radical-mediated reactions but could also be due to destabilizing effects of increases in thiol/disulfide ratios in the plasma, which normally is in a more oxidized state than intracellular compartments. Changes in the thiol redox gradient across cells could also adversely affect any transport or cell signaling processes, which are dependent on formation and rupture of disulfide linkages in membrane proteins. Therapeutic thiol administration has been shown to have great potential, and its efficacy should be increased by selecting compounds and methods of delivery that will minimize perturbations in the thiol status of regions external to the targeted areas.

Regulation of gene expression by reactive oxygen

Reactive oxygen intermediates are produced in all aerobic organisms during respiration and exist in the cell in a balance with biochemical antioxidants. Excess reactive oxygen resulting from exposure to environmental oxidants, toxicants, and heavy metals perturbs cellular redox balance and disrupts normal biological functions. The resulting imbalance may be detrimental to the organism and contribute to the pathogenesis of disease and aging. To counteract the oxidant effects and to restore a state of redox balance, cells must reset critical homeostatic parameters. Changes associated with oxidative damage and with restoration of cellular homeostasis often lead to activation or silencing of genes encoding regulatory transcription factors, antioxidant defense enzymes, and structural proteins. In this review, we examine the sources and generation of free radicals and oxidative stress in biological systems and the mechanisms used by reactive oxygen to modulate signal transduction cascades and redirect gene expression.

Cardiac dilatation associated with collagen alterations

There is a complex collagen network in the heart. Various components have been identified and generally on the basis of form and position some functions have been ascribed to one or another of these components. Since the various components all appear to be connected in a hierarchial network of some type assigning function is not difficult but demonstrating a given function is somewhat hazardous. We have demonstrated that two I.V. infusions of disulfide reagents one week apart activates a collagenolytic system that results in near complete loss of the collagen struts that interconnect myocytes, the collagen struts that connect capillaries to all adjacent myocytes and the weave complex that surrounds groups of myocytes. Increases in pre load or afterload result in responses indicating that the disulfide treated animals generate pressure equal to or greater than the control hearts, thus, the treatment has no affect on either myocyte contractility or force delivery to the ventricle. However, static pressure volume measurements in the disulfide treated animals are shifted far to the right indicating marked dilatation of the ventricle and increase in distensibility. This indicates that the weave complex contributes to the initial rectilinear portion of the pressure volume curve.

Pericellular substrates of human mast cell tryptase: 72,000 dalton gelatinase and fibronectin

Migrating cells degrade pericellular matrices and basement membranes. For these purposes cells produce a number of proteolytic enzymes. Mast cells produce two major proteinases, chymase and tryptase, whose physiological functions are poorly known. In the present study we have analyzed the ability of purified human mast cell tryptase to digest pericellular matrices of human fibroblasts. Isolated matrices of human fibroblasts and fibroblast conditioned medium were treated with tryptase, and alterations in the radiolabeled polypeptides were observed in autoradiograms of sodium dodecyl sulphate polyacrylamide gels. It was found that an M(r) 72,000 protein was digested to an M(r) 62,000 form by human mast cell tryptase while the plasminogen activator inhibitor, PAI-1, was not affected. Cleavage of the M(r) 72,000 protein could be partially inhibited by known inhibitors of tryptase but not by aprotinin, soybean trypsin inhibitor, or EDTA. Fibroblastic cells secreted the M(r) 72,000 protein into their medium and it bound to gelatin as shown by analysis of the medium by affinity chromatography over gelatin-Sepharose. The soluble form of the M(r) 72,000 protein was also susceptible to cleavage by tryptase. Analysis using gelatin containing polyacrylamide gels showed that both the intact M(r) 72,000 and the M(r) 62,000 degraded form of the protein possess gelatinolytic activity after activation by sodium dodecyl sulphate. Immunoblotting analysis of the matrices revealed the cleavage of an immunoreactive protein of M(r) 72,000 indicating that the protein is related to type IV collagenase. Further analysis of the pericellular matrices indicated that the protease sensitive extracellular matrix protein fibronectin was removed from the matrix by tryptase in a dose-dependent manner. Fibronectin was also susceptible to proteolytic degradation by tryptase. The data suggest a role for mast cell tryptase in the degradation of pericellular matrices.

Role of Glutathione Peroxidase in Rheumatoid Arthritis: Analysis of Enzyme Activity and DNA Polymorphism

Aberrant expression of the antioxidant enzyme glutathione peroxidase (GPx) could contribute to the etiology of rheumatoid arthritis (RA). However, previous enzyme activity studies examining this relationship were inconclusive. Indirect evidence for this relationship derives from the known efficacy of gold therapy in RA, since gold compounds specifically inhibit GPx. The hypothesis that variants of GPx are associated with RA was examined by two approaches: enzyme activity analysis and restriction fragment length polymorphism (RFLP) association analysis. No significant difference was found in whole blood GPx activity between 28 RA patients and 36 controls. GPx activity appeared to be independent of sex, race, or type of drug treatment. However, a statistically significant difference was found with respect to treatment responsiveness. RA patients classified as good responders to gold therapy, but who were no longer taking gold, had a significantly higher GPx activity compared to both the controls and good responders currently on gold therapy. Aberrantly high GPx activity could contribute to RA by generating excess oxidized glutathione, a potent collagenase activator. Gold therapy would reduce GPx activity to normal levels. The restriction enzyme Pvu II in conjunction with a GPx gene probe identified a useful RFLP (Al, 22 kbp; A2, 15 kbp) with allelic frequencies of A1 and A2 equal to 0.11 and 0.89, respectively, in the control population. No statistically significant association, however, could be demonstrated between this allelic variant of the GPx gene and RA.

Selenium in rheumatic diseases

Selenium is involved in several important biochemical pathways relevant to rheumatic diseases. Experimental and clinical studies suggest that selenium modulates the inflammatory and immune responses. Patients suffering from inflammatory rheumatic diseases often have low selenium levels, but this finding does not correlate with disease severity. Selenium supplementation needs stricter selection criteria and better ascertainment of dose to obtain a stimulatory or inhibitory effect relevant to the disease state. Prevention of marginal selenium deficiency by moderate supplementation might enhance host defense mechanisms.

The cysteine switch: a principle of regulation of metalloproteinase activity with potential applicability to the entire matrix metalloproteinase gene family

The general applicability of the "cysteine-switch" activation mechanism to the members of the matrix metalloproteinase (MMP) gene family is examined here. All currently known members of the MMP gene family share the characteristic that they are synthesized in a latent, inactive, form. Recent evidence suggests that this latency in human fibroblast collagenase (HFC) is the result of formation of an intramolecular complex between the single cysteine residue in its propeptide domain and the essential zinc atom in the catalytic domain, a complex that blocks the active site. Latent HFC can be activated by multiple means, all of which effect the dissociation of the cysteine residue from the complex. This is referred to as the "cysteine-switch" mechanism of activation. The propeptide domain that contains the critical cysteine residue and the catalytic domain that contains the zinc-binding site are the only two domains common to all of the MMPs. The amino acid sequences surrounding both the critical cysteine residue and a region of the protein chains containing two of the putative histidine zinc-binding ligands are highly conserved in all of the MMPs. A survey of the literature shows that many of the individual MMPs can be activated by the multiple means observed for latent HFC. These observations support the view that the cysteine-switch mechanism is applicable to all members of this gene family. This mechanism is unprecedented in enzymology as far as we know and offers the opportunity for multiple modes of physiological activation of these important enzymes. Since conditions in different cells and tissues may match those necessary to effect one of these activation modes for a given MMP, this may offer metabolic flexibility in the control of MMP activation.

Characterization and activation of procollagenase from human polymorphonuclear leucocytes. N-terminal sequence determination of the proenzyme and various proteolytically activated forms

Procollagenase of human polymorphonuclear leucocytes was purified to homogeneity using a rapid and reproducible method. The purification procedure included affinity chromatography on zinc chelate Sepharose, ion exchange chromatography on Q-Sepharose fast flow, followed by affinity chromatography on orange Sepharose and finally a gel-permeation step on Sephacryl S-300. It was shown by SDS/PAGE, under reducing conditions, that the latent collagenase of human polymorphonuclear leucocytes consists of a single polypeptide chain with an apparent relative molecular mass of 85,000. Upon deglycosylation by endoglycosidase F digestion, the apparent relative molecular mass of the procollagenase was reduced to 53,000 which is similar to that of the fibroblast enzyme, and indicates a close relationship between both enzymes. Sequence data were determined by direct automated Edman degradation of the purified polymorphonuclear leucocyte procollagenase. The complete sequence of the propeptide region (residue 1-120) was thereby established. The proteolytic activation of the polymorphonuclear leucocyte procollagenase by various enzymes was investigated by determining the N-terminal sequences of the intermediate and final activated forms. Activation by chymotrypsin and cathepsin G led to the active form (Mr 64,000) by cleaving 79 N-terminal residues from the proenzyme. Trypsin activates in a two-step process. Cleavage of 48 N-terminal residues led to a still latent Mr 70,000 species. The final active form (Mr 65,000) was obtained by splitting off 20 additional N-terminal residues.

Activation of hepatocyte protein kinase C by redox-cycling quinones

The effects of quinone-generated active oxygen species on rat hepatocyte protein kinase C were investigated. The specific activity of cytosolic protein kinase C was increased 2-3-fold in hepatocytes incubated with the redox-cycling quinones, menadione, duroquinone or 2,3-dimethoxy-1,4-naphthoquinone, without alterations in particulate protein kinase C specific activity or Ca2+- and lipid-independent kinase activities. Redox-cycling quinones did not stimulate translocation of protein kinase C; however, activated protein kinase C was redistributed from cytosol to the particulate fraction when quinone-treated hepatocytes were exposed to 12-O-tetradecanoylphorbol 13-acetate (TPA). Quinone treatment did not alter cytosolic phorbol 12,13-dibutyrate (PDBu) binding capacity, and the cytosol of both control and quinone-treated hepatocytes exhibited a Kd for PDBu binding of 2 nM. Quinone-mediated activation of cytosolic protein kinase C was reversed by incubation with 10 mM-beta-mercaptoethanol, dithiothreitol or GSH, at 4 degrees C for 24 h. Furthermore, protein kinase C specific activity in control cytosol incubated in air increased by over 100% within 3 h; this increase was reversed by thiol-reducing agents. Similarly, incubation of partially-purified rat brain protein kinase C in air, or with low concentrations of GSSG in the presence of GSH, resulted in a 2-2.5-fold increase in Ca2+- and lipid-dependent kinase activity. In contrast with the effects of the redox-cycling quinones, when hepatocytes were treated with the thiol agents N-ethylmaleimide (NEM), p-benzoquinone (pBQ) or p-chloromercuribenzoic acid (pCMB), the cytosolic Ca2+- and lipid-dependent kinase activity was significantly inhibited, but the particulate-associated protein kinase C activity was unaffected. The Ca2+- and lipid-independent kinase activity of both the cytosolic and particulate fractions was significantly stimulated by NEM, but was unaffected by pBQ and pCMB. These results show that hepatocyte cytosolic protein kinase C is activated to a high-Vmax form by quinone-generated active oxygen species, and this effect is due to a reduction-sensitive modification of the thiol/disulphide status of protein kinase C.

The inhibition of a tumour cell surface protease in vivo and its re-activation by oxidation

Colonic tumour cells possess a cell surface protease capable of binding 9-aminoacridine to its active centre, thus locating cells when viewed under a fluorescence microscope. In vivo and in frozen sections, the enzyme is masked by a protein inhibitor. This inhibitor can be displaced by formaldehyde fixation of the tissue and then replaced by adding a fresh extract of colon or lung tissue. The inhibitor is modified by oxidation; provided by air, oxidized glutathione or potassium permanganate, resulting in a change in conformation in the inhibitor and this then results in the enzyme binding the fluorescent probe. The effect of oxidation can be reversed by dithiothreitol. It is proposed that these changes are brought about by a disulphide exchange acting on the inhibitor which indirectly controls the activity of the cell surface enzyme in vivo. The steps described above can be conveniently followed on sections of tissue mounted on a microscope slide; this has the advantage that the same cells can be monitored during a sequence of reactions. It is believed that these techniques could well be applied to other enzyme systems than the tumour protease described in this study.

Respiratory burst facilitates the digestion of Escherichia coli killed by polymorphonuclear leukocytes

We examined factors that may limit degradation of bacterial protein of Escherichia coli S15 killed by polymorphonuclear leukocytes (PMN). Both human and rabbit PMN degraded up to 40% of [14C]amino acid-labeled protein of ingested and killed E. coli in 2 h as determined by loss of acid-precipitable radioactivity. In contrast, equally bactericidal broken-PMN preparations or isolated granules degraded only about 10% of bacterial protein regardless of pH. To determine whether activation of the respiratory burst contributes to digestion, we compared degradation by intact PMN in room air and under N2. Depletion of O2 by N2 flushing had no effect on the bactericidal activity of either human or rabbit PMN but reduced degradation by approximately 50%. Protein degradation during phagocytosis was also reduced in the presence of cyanide or azide, inhibitors of myeloperoxidase (MPO). PMN of two patients with chronic granulomatous disease ingested and killed E. coli S15 as well as did normal PMN but degraded bacterial protein as did normal PMN incubated under N2. The low degradative activity of PMN disrupted by sonication could be raised to nearly the level of intact PMN incubated in room air by preincubation of the PMN with 10(-7) M formyl-methionyl-leucyl-phenylalanine (fMLP) before sonication and by pretreatment of E. coli with MPO. Depletion of O2 or chloride during these preincubations with formyl-methionyl-leucyl-phenylalanine respectively, virtually abolished and markedly diminished stimulation of bacterial protein degradation. We conclude that enhanced MPO-mediated O2 metabolism of intact PMN plays a role in the digestion of killed E. coli.

Degradation of human glomerular basement membrane by stimulated neutrophils. Activation of a metalloproteinase(s) by reactive oxygen metabolites

We examined the role of reactive oxygen metabolites in the degradation of human glomerular basement membrane (GBM) by stimulated human neutrophils. Neutrophils stimulated with phorbol myristate acetate (PMA) caused a significant degradation of GBM over 3 h resulting in 11.4 +/- 0.9% (SEM), n = 11 release of hydroxyproline compared with 0.3 +/- 0.09%, n = 11 release by unstimulated neutrophils. Superoxide dismutase, a scavenger of superoxide, did not inhibit the GBM degradation, whereas catalase, a scavenger of hydrogen peroxide, caused a marked inhibition (-60 +/- 7%, n = 4, P less than 0.001) of hydroxyproline release. Neither alpha-1 proteinase inhibitor, an inhibitor of elastase, nor soya bean trypsin inhibitor, an inhibitor of cathepsin G, caused any significant inhibition of GBM degradation. GBM degradation by cell-free supernatants obtained from stimulated neutrophils was markedly impaired in the presence of metal chelators EDTA (-72 +/- 7, n = 6, P less than 0.001) and 1,10,phenanthroline (-85 +/- 5%, n = 3, P less than 0.001). Considering these results, we postulated that reactive oxygen metabolites generated by the stimulated neutrophils activate a latent GBM degrading metalloproteinase(s). GBM degradation by supernatants obtained from incubations with catalase, azide, an inhibitor of myeloperoxidase, and methionine and taurine, scavengers of hypochlorous acid, was markedly reduced. Our data thus indicate that degradation of the GBM by PMA-stimulated neutrophils is due to activation of a latent metalloproteinase by hypochlorous acid or a similar oxidant generated by the myeloperoxidase-hydrogen peroxide-halide system.

Gold sodium thiomalate activates latent human leukocyte collagenase

Gold sodium thiomalate, a drug used widely in the therapy of rheumatoid arthritis, was found to be an activator of latent human polymorphonuclear leukocyte collagenase. The activation was demonstrated by two distinct and independent collagenase assays: by recording with a spectrophotometer at 227 nm the enzyme-induced increase in ultraviolet difference absorbance of native type I collagen connected to the cleavage of collagen at 37 degrees C [(1986) Eur. J. Biochem. 156, 1-4] and by SDS-polyacrylamide gel electrophoresis analysis of formation of specific products of collagen resulting from collagenase cleavage at 25 degrees C. Activation of latent collagenase by gold sodium thiomalate appeared to be of the same magnitude as by the known activator phenylmercuric chloride.

The effect of insulinomimetic agents on protein degradation in H35 hepatoma cells

A wide variety of agents are shown to mimic insulin action and inhibit rates of intracellular protein degradation in H35 hepatoma cells. For oxidizing agents such as NaNO2, H2O2 and oxidized glutathione, inhibition of protein breakdown is reversed by adding catalase. Phenylhydrazine behaves like an oxidant and mimics insulin action in a manner potentiated by superoxide dismutase and reversed by catalase. Similarly the effect of insulin itself is increased by superoxide dismutase and reduced by catalase. Sulfhydryl reagents also mimic insulin action: inhibition of protein breakdown is seen following addition of 2-mercaptoethanol or a brief pre-treatment with N-ethylmaleimide or iodoacetate. Mild pre-treatment with trypsin also inhibits subsequent rates of protein breakdown. A model is proposed suggesting that these insulinomimetic actions involve a common mechanism which links the generation of active oxygen species through the redox potential of the cell to the activation of a proteinase.

Oxygen radicals as effectors of cartilage destruction. Direct degradative effect on matrix components and indirect action via activation of latent collagenase from polymorphonuclear leukocytes

Degradation of intact cartilaginous tissue (bovine nasal cartilage) by oxygen-derived free radicals (ODFR) generated enzymatically by xanthine oxidase and hypoxanthine was studied. The degree of tissue destruction was determined by measuring the indentation under a defined compression force as well as by the loss of uronic acid- and hydroxyproline-containing matrix components. Cartilage slices altered by prior elastase treatment were more susceptible to oxygen radical attack than were intact tissue specimens. Degradation of cartilage matrix by ODFR was strongly inhibited by superoxide dismutase or catalase. Coincubation of latent collagenase from polymorphonuclear leukocytes with the ODFR-generating system led to activation of collagenolytic activity, resulting in marked degradation of the bovine cartilage slices. In further studies, activated polymorphonuclear leukocyte-collagenase was shown to degrade intact human articular cartilage to a degree of mechanical insufficiency. Thus, our assay system serves as an in vitro model of tissue damage, which may be relevant to pathophysiologic states such as rheumatoid arthritis.

On the mechanism of the chemical modification of the mitochondrial acetyl-CoA acetyltransferase by coenzyme A

The liver mitochondrial acetyl-CoA acetyltransferase (acetyl-CoA:acetyl-CoA C-acetyltransferase, EC 2.3.1.9), is involved in ketone body synthesis. The enzyme can be chemically modified and inactivated by CoASH and also by CoASH-disulfides provided glutathione is present. The unmodified enzyme shows in its denatured state 7.95 +/- 0.44 sulfhydryl groups per enzyme and in its native state 3.92 +/- 0.34 sulfhydryl groups which react with Ellmann's reagent. The modified enzyme reveals in its native state also 4.07 +/- 0.25 sulfhydryl groups per enzyme, but in its denatured state 9.10 +/- 0.51 sulfhydryl groups could be detected. Approximately four sulfhydryl groups per enzyme, unmodified or modified, can be alkylated by iodoacetamide. These results prove for each subunit the existence of two sulfhydryl groups and suggest the existence of two disulfide bridges. The CoASH modification, which should proceed at one of these disulfide groups, prevents subsequent acetylation of the enzyme and is drastically reduced in the iodoacetamide-alkylated enzyme. In the demodification of the modified enzyme, the CoASH is set free as a mixed disulfide with glutathione.

Release of thioltransferase from rabbit polymorphonuclear leucocytes by immune complex in vitro and inhibition of the enzyme by chloramphenicol

Immune complex induced the release of thioltransferase from rabbit peritoneal exudates polymorphonuclear leucocytes in vitro. The release of thioltransferase occurs from viable cells and does not depend on a cytolysis. The catalytic activity of the released enzyme with S-sulfocysteine and glutathione as substrates had a distinct optimum pH at 7.6. On the contrary, opsonized zymosan was not effective as a stimulus for the liberation of thioltransferase from polymorphonuclear leucocytes. Thioltransferase liberated by the stimulation with immune complex was inhibited by chloramphenicol, but not by bacitracin. The inhibition was non-competitive (apparent Ki of 0.2 mM).

Redox status of cultured fibroblasts. Possible relations with specific catabolic rates of proteoglycans

In cultured embyonic rat fibroblast the cytoplasmic NAD/NADH ratio was determined from the lactate/pyruvate ratio under acidic, hypoxic and lactic acid-rich conditions.

RESULTS AND CONCLUSIONS

The NAD/NADH ratio is reduced when the lactate concentration increases at pH 7.4 with and without hypoxia. At pH 6.6 this ratio is not reduced by lactate in normoxia: Conditions of aerobic glycolysis did not increase NADH. The NAD/NADH ratio was strongly lowered at pH 6.6 by lactate plus hypoxia. At low cell density this condition of hypoxic glycolysis is correlated with the increase of the specific activities of CS- and DS-proteoglycans (DS much greater than CS). But only the CS concentration was increased. Conditions of aerobic glycolysis at low cell density caused a moderate increase of both the specific activity and concentration of DS. The different regulation of the turnover of CS- and DS-proteoglycans is suggested to be based on their different synthetic capacities (CS greater than DS) on the one side and on the effect of specifically acting proteoglycanases on the other side. Maximal degradation of proteoglycans seems to be stimulated by NADH-activated proteases, supposedly thiol proteases. Lower degradation seems to be effectuated under non-reductive acidic conditions. Both these types of degradation seem stronger to affect DS-proteoglycan. Some neutral proteases seem stronger to affect CS-proteoglycan. Improved oxygen supply might reduce the CS concentration in proliferating tissue, such as in chronic inflammation, and thus reduce this process.

Solubilization and partial characterization of the intestinal receptor for Escherichia coli heat-stable enterotoxin

Binding of Escherichia coli strain 431 heat-stable enterotoxin (STa) and activation of intestinal particulate guanylate cyclase by E. coli STa were studied with rat intestinal epithelial cells and brush border membranes (BBMs). The rates of guanylate cyclase stimulation by 431 STa in cells and BBMs were rapid, with maximal levels of cyclic GMP observed within 5 min. Specific binding of 125I-labeled STa from E. coli 431 (431 125I-STa) and activation of guanylate cyclase by unlabeled 431 STa were observed with intestinal BBMs; however, neither was detected with membranes from nonintestinal tissues. The STa receptor was solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, a nondenaturing dipolar ionic detergent, in yields of approximately 50%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the detergent-solubilized receptor-431 125I-STa complex, followed by autoradiography, showed that 431 125I-STa bound to a single BBM component with a molecular weight of about 100,000. Binding of 431 STa to its solubilized receptor was saturable, specific, and essentially irreversible. Pretreatment of the soluble receptor with trypsin and pronase but not chymotrypsin decreased binding of 431 125I-STa. The 431 STa-receptor complex was dissociated by boiling in the presence of 1% sodium dodecyl sulfate, incubation with 0.5 M acetic acid, or reduction with dithiothreitol. In contrast to the residual particulate guanylate cyclase activity of detergent-treated membranes, solubilized guanylate cyclase was not stimulated by STa. Membrane structure appears to play an important role in the coordination of STa binding and stimulation of guanylate cyclase activity.

Latent collagenase of rheumatoid synovial fluid is not of granulocytic origin

The physicochemical properties of three latent collagenases derived from rheumatoid synovial fluid, polymorphonuclear leucocytes and culture medium of rheumatoid synovium were compared. It has been shown that synovial fluid enzyme is similar to that of synovium collagenase from tissue culture and differs significantly in molecular size and protein charge from granulocyte collagenase. The results indicate that the latent, trypsin-activable collagenase present in rheumatoid synovial fluid is not of granulocytic origin and seems to derive from the synovial membrane.

Histamine, 5-hydroxytryptamine and compound 48/80 activate PMN-leucocyte collagenase of the rat

Experimental pleurisy in rat and intraperitoneal injection of histamine, serotonin and the histamine releaser compound 48/80 caused changes in blood leucocyte populations. An increased number of PMN-leucocytes was observed. The peripheral blood PMN-leucocytes of non-treated rats contained collagenase mainly in the latent form. During experimental pleurisy and after treatment with histamine, serotonin and compound 48/80 activation of latent collagenase of up to 90-98% was obtained. Mepyramine, cimetidine and timegadine inhibited activation of latent collagenase by compound 48/80. It is suggested that histamine is involved in the process of activation of leucocyte collagenase in the course of inflammation.

Modulation of rat-liver mitochondrial acetyl-CoA acetyltransferase activity by a reversible chemical modification with coenzyme A

The mitochondrial acetyl-CoA acetyltransferase (acetoacetyl-CoA thiolase, EC 2.3.1.9) is involved in ketone body biosynthesis. In its unmodified state, referred to as transferase B in former publications (Huth, W. (1981) Eur. J. Biochem. 120, 557-562), the enzyme is characterized by the highest specific activity of 21.65 mumol/min per mg protein (direction of acetoacetyl-CoA synthesis); several forms of the enzyme with lower specific activities result from chemical modification by an apparent covalent binding of CoASH. The chemical modification results in an inactivation of the enzyme: a 2 h incubation with 0.2 mM CoASH at pH 8.1 at 30 degrees C inactivates up to 95%. Both processes, the CoASH-binding and the resulting inactivation, can be simultaneously reversed by treatment with glutathione. The specificity of inactivation is limited to CoASH and the intact sulfhydryl group is a prerequisite for this process. The enzyme exhibits a limited number (n = 3.2) of high-affinity (Ka = 26.7 microM) specific binding sites for CoASH. The inactivation-reactivation cycle of acetyl-CoA acetyltransferase by CoASH and glutathione may involve a protein disulfide-thiol exchange and represents a mode of control in modulating the amount of active enzyme.

Reversible inactivation of Saccharomyces cerevisiae glutathione reductase under reducing conditions

Glutathione reductase from Saccharomyces cerevisiae was rapidly inactivated following aerobic incubation with NADPH, NADH, and several other reductants, in a time- and temperature-dependent process. The inactivation had already reached 50% when the NADPH concentration reached that of the glutathione reductase subunit. The inactivation was very marked at pH values below 5.5 and over 7, while only a slight activity decrease was noticed at pH values between these two values. After elimination of excess NADPH the enzyme remained inactive for at least 4 h. The enzyme was protected against redox inactivation by low concentrations of GSSG, ferricyanide, GSH, or dithiothreitol, and high concentrations of NAD(P)+; oxidized glutathione effectively protected the enzyme at concentrations even lower than GSH. The inactive enzyme was efficiently reactivated after incubation with GSSG, ferricyanide, GSH, or dithiothreitol, whether NADPH was present or not. The reactivation with GSH was rapid even at 0 degree C, whereas the optimum temperature for reactivation with GSSG was 30 degrees C. A tentative model for the redox interconversion, involving an erroneous intramolecular disulfide bridge, is put forward.

Collagenase activity in the granulocytes of patients with various liver diseases

Studies were conducted on collagenase activity on peripheral granulocytes of patients with various liver diseases. Total collagenase activity increased significantly in chronic active hepatitis (CAH) and in liver cirrhosis (LC), and, in these disorders, it correlated with the extent to which hepatic fibrosis has progressed. Active collagenase activity increased in CAH, but no differences from normal controls were found in other liver diseases. These results suggest that total collagenase may reflect the degree of hepatic fibrosis, and that active collagenase may be related to chronic active hepatitis lesions.

Characterisation of beta 1-anticollagenase from human plasma and its reaction with polymorphonuclear leukocyte collagenase by disulfide/thiol interchange

A beta 1-serum component, beta 1-anticollagenase, capable of inhibiting various mammalian tissue collagenases, was isolated from human plasma by gel filtration, affinity chromatography and ion-exchange chromatography. The inhibitor contains 1-2 free sulfhydryl groups, which are a prerequiste for inhibitory activity and for binding to the thiol-Sepharose affinity support. Alkylation of beta 1-anticollagenase by iodoacetamide blocks inhibitory activity. The inhibitor was purified to apparent homogeneity and exhibited a Mr = 30500 determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The amino acid and carbohydrate composition was determined. According to its composition and the isoelectric focussing beta 1-anticollagenase is an acidic protein with an isoelectric point of 5.6. Inhibition of human leukocyte collagenase proceeds in a strong 1 : 1 stoichiometric reaction. The mechanism of this association takes place by a disulfide/thiol interchange reaction as has been previously indicated for human leukocyte collagenases in forming the latent enzyme [Macartney, H. W. and Tschesche, H. (1980) FEBS Lett. 119, 327-332]. The beta 1-anticollagenase--leukocyte-collagenase complex (latent enzyme) is activatable by disulfide-containing compounds such as cystine, oxidised glutathione, insulin, relaxin, trypsinogen and others, but not by 179,203-di(S-carboxymethyl)trypsinogen, or its trypsin derivative. Compounds containing inaccessible disulfide bonds, e.g. chymotrypsin, or sulfhydryl groups, e.g. D-penicillamine, do not activate the complex. Activation is, however, easily obtained with the oxidised-glutathione-generating system myeloperoxidase/H2O2/glutathione as was previously demonstrated for the human leukocyte latent collagenase activatable in a phagocytosis-simulated respiratory burst [Tschesche, H. and Macartney, H. W. (1981) Eur. J. Biochem. 120, 183-190].