Biomedical subjects

T Grune

Publications and source records attributed to T Grune.

At least 73 records · Page 4Linked to original sources

PubMed1998

Dose- and wavelength-dependent oxidation of crystallins by UV light--selective recognition and degradation by the 20S proteasome.

The lens of the human eye is a suitable model for age-related alterations at the molecular level. Age-related cataract formation is closely related to the accumulation of oxidatively altered proteins. In this study the influence of UV-A, UV-B, and UV-C irradiation on the proteolytic susceptibility of alpha-, betaL-, and betaH-crystallins by the isolated 20S proteasome was investigated. The proteins were irradiated with 280, 300, and 350 nm monochromatic light. Changes of the physical properties of the crystallins were characterized by absorbance measurements at 280 nm, fluorescence spectra, and SDS-PAGE-electrophoresis. The proteolytic susceptibility of crystallins was maximal after irradiation at 280 nm and three- to fivefold lower at 300 nm. Irradiation at 350 nm was not able to initiate proteolysis, probably due to protein-aggregate formation of higher molecular weight, as shown by SDS-PAGE. The damage of crystallins by UV-C light might be a signal for its proteolytic degradation by the 20S proteasome, whereas UV-B and UV-A do not increase the proteolytic susceptibility to the same extent but promote the formation of crosslinked proteins. Therefore, irradiation with UV, which is not followed by an increase in the proteolytic susceptibility, is accompanied by the formation of crosslinked proteins. It was concluded, that also long UV-B and UV-A may be involved in age-related alterations of the human lens and cataract formation.

Crystallins↗

PubMed1998

Does long-term treatment of renal anaemia with recombinant erythropoietin influence oxidative stress in haemodialysed patients?

BACKGROUND: Patients with end-stage renal failure undergoing haemodialysis (HD) are exposed to oxidative stress. Increased levels of malondialdehyde (MDA) were demonstrated in plasma of uraemic patients, indicating accelerated lipid peroxidation (LPO) as a consequence of multiple pathogenetic factors. The aim of our investigation was to examine the role of renal anaemia in oxidative stress in HD patients. METHODS: MDA and 4-hydroxynonenal (HNE) were measured in three groups of patients undergoing HD: group I comprised eight patients with a blood haemoglobin (Hb) < 10 g/dl (mean Hb = 8.1+/-1.3 g/dl), and group II were eight patients with a Hb > 10 g/dl (mean Hb=12.4+/-1.9g/dl); none of these 16 patients had been treated with human recombinant erythropoietin (rHuEpo). Group III comprised 27 patients with a mean Hb of 10.5+/-1.6 g/dl after long-term rHuEpo treatment. RESULTS: Mean plasma concentrations of both MDA and HNE were significantly higher (P<0.0001) in all 43 HD patients than in 20 healthy controls (MDA 2.85+/-0.25 vs 0.37+/-0.03 microM, HNE 0.32+/-0.03 vs 0.10+/-0.01 microM). Comparing the three groups, it was shown that HD patients with a Hb <10 g/dl had significantly higher plasma levels of LPO products (MDA 3.81+/-0.86 microM, HNE 0.45+/-0.07 microM) than HD patients with a Hb >10g/dl (MDA 2.77+/-0.58 UM, HNE 0.25+/-0.05 microM), and than HD patients treated with rHuEpo (MDA 2.50+/-0.12 microM, HNE 0.29+/-0.03 microM). Furthermore, an inverse correlation between plasma concentration of LPO products and haemoglobin levels was seen (r=0.62, P<0.0001). CONCLUSION: Radical generation in HD patients might be caused in part by renal anemia itself. Treatment with rHuEpo may decrease radical generation effectively in HD patients due to the increase in the number of red blood cells and blood haemoglobin concentration.

Adult↗

PubMed1998

Metabolism of 4-hydroxynonenal, a cytotoxic lipid peroxidation product, in thymocytes as an effective secondary antioxidative defense mechanism.

The metabolism of the aldehydic lipid peroxidation product, 4-hydroxynonenal (HNE),was studied in suspensions of mouse thymocytes. Thymocytes are characterized by low lipid peroxidation in comparison with other cell types notwithstanding their high content of arachidonic acid. In our study a very high capacity of HNE metabolism in thymocytes was observed: 27.7 nmol/mg w.w./min. That is about the same HNE degradation rate as determined in liver cells or small intestinal enterocytes, which are the cells with the by far highest capacity for the degradation of HNE and other aldehydic lipid peroxidation products in comparison with other cell types. The primary and secondary HNE metabolites in thymocytes were identified and quantified after the addition of 100 microM HNE to thymocyte suspensions: the glutathione-HNE conjugate, the hydroxynonenoic acid, the 1,4-dihydroxynonene, water, and the glutathione-dihydroxynonene conjugate. Furthermore, the HNE binding to proteins was measured. The very rapid HNE degradation in thymocytes besides the high amounts of lipophilic chain-breaking antioxidants is postulated to be an important secondary antioxidative mechanism and the main factor for the low accumulation of lipid peroxidation products in these cells.1668

Aldehydes↗

PubMed1998

Parenteral selenium supplementation in critically ill patients--effects on antioxidant metabolism.

Decreased plasma selenium (Se) levels are common in critically ill patients. Oxidative stress is regarded as one possible cause of the Se deficiency. We investigated in 20 critically ill patients with decreased plasma selenium concentrations the antioxidant metabolism during parenteral selenium supplementation (week 1: 2 x 500 micrograms; week 2:1 x 500 micrograms, week 3:3 x 100 micrograms sodium selenite). As marker of oxidative stress we measured the plasma malondialdehyde levels on days 0, 1, 3, 7, 14, and 21. The content of reduced and oxidized glutathione as well as the leucocyte activity marker elastase were estimated on the same days. Initial plasma Se levels were considerably decreased (0.44 +/- 0.1 mumol/l, mean +/- SEM). After one day of supplementation Se concentrations were in the reference range. Plasma malondialdehyde levels and the ratio of oxidized and reduced glutathione were initially elevated and decreased beginning on day 3 of supplementation. The mean elastase level was 113 +/- 10 micrograms/l on day 0. On day 3 elastase values decreased significantly (85 +/- 13 micrograms/l, p < 0.05; day 21, 19 +/- 7 micrograms/l, p < 0.001). Antioxidant metabolism showed significant changes beginning after 72 hours of therapy. This latency may be explained with the induction of the enzyme glutathione peroxidase. The lowered plasma Se concentrations measured in the critically ill patients and the significant effects on antioxidant metabolism during supplementation emphasized the importance of selenium administration in these patients.

Adult↗

PubMed1997

Detection of 8-hydroxydeoxyguanosine in K562 human hematopoietic cells by high-performance capillary electrophoresis.

A method for the detection of 8-hydroxydeoxyguanosine by high-performance capillary electrophoresis (HPCE) was developed. Separations were performed in an uncoated silica capillary (44 cm x 75 microns i.d.) with a P/ACE system with diode-array detector. The separation of purine deoxynucleosides and 8-hydroxydeoxyguanosine was optimized with regard to pH, temperature, applied potential and hydrodynamic injection time. Optimum conditions were 20 mM borate buffer (pH 9.5), 25 degrees C, 25 kV, 20 s load and detection at 254 nm. This method allowed the detection of 8-hydroxydeoxyguanosine in the presence of a 10(5)-fold higher amount of deoxyguanosine. Isolated nuclei from K562 human hematopoietic cells were treated with 15 mM hydrogen peroxide for 2 h. The nuclei were extensively dialyzed and DNA was isolated, enzymatically hydrolyzed to the deoxynucleosides and analyzed by HPCE. DNA from hydrogen peroxide treated nuclei had a 4-fold higher content of 8-hydroxydeoxyguanosine than untreated controls. HPCE analysis of 8-hydroxydeoxyguanosine is fast and simple. Furthermore, it requires a very small sample volume, which makes it useful for biomedical and clinical applications.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed1997

Evaluation of purine nucleotide loss, lipid peroxidation and ultrastructural alterations in post-hypoxic hepatocytes.

1. Hypoxic alterations in isolated rat hepatocytes were demonstrated by a 90% ATP loss during 60 min of ischaemia and temporary increases of nucleotide degradation products. 2. The oxidative stress during reoxygenation was demonstrated in these cells by a decrease in reduced glutathione (GSH) concentration (30%) and a threefold increase in lipid peroxidation products such as 4-hydroxynonenal and thiobarbituric acid-reactive substances (TBA-RSs). The tremendous GSH loss could not be balanced by the slight oxidized glutathione (GSSG) increase during reoxygenation. 3. For the first time the involvement of free radicals was directly demonstrated using electron spin resonance (ESR) spectroscopy in reoxygenated liver cells. Using the spin trap 5,5-dimethylpyrroline-1-oxide (DMPO), a carbon-centred radical and the adduct of the hydroxyl radical could be detected during early reoxygenation. 4. Morphological alteration of cells was observed, beginning during hypoxia and increasing during post-hypoxic reoxygenation. Electron microscopic findings of hypoxic and post-hypoxic cell damage included pyknosis of nuclei, spherical transformation of mitochondria and increased number of vesicles.

Aldehydes↗

PubMed1997

Breakdown of oxidized proteins as a part of secondary antioxidant defenses in mammalian cells.

The degradation of oxidized proteins is an essential part of antioxidant defenses against free radical attack. Selective degradation of oxidatively damaged proteins allows proteolytic systems to function directly in the removal of useless cellular debris and therefore prevent the accumulation of potentially toxic fragments or large aggregates of cross-linked proteins. The degradation of oxidized proteins in dividing mammalian cells after hydrogen peroxide treatment has been demonstrated. Cells are able to increase proteolysis rates after treatment with moderate levels of oxidants. The role of proteasome in the removal of oxidized proteins has been demonstrated by treatment of cells with an anti-sense oligodesoxynucleotide to the proteasome C2 subunit gene. This treatment decreases the proteasome content of the cells and prevents increased proteolysis rates after hydrogen peroxide treatment. Thus proteasome clearly plays a role in the removal of oxidized proteins. As part of antioxidant defenses the proteasome provides a second line of defense against the numerous radicals and oxidants which contact cells during their lifetime. The degradation of oxidatively damaged proteins enables-cells to recover from a moderate oxidant attack.

Animals↗

PubMed1997

Differential response of oxygen radical metabolism in rat heart, liver and kidney to cyclosporine A treatment.

OBJECTIVE AND DESIGN: The study was designed to elucidate whether cyclosporine A (Cy A) induces oxidative stress in heart, liver and kidney. MATERIAL AND TREATMENT: Male Wistar rats were treated with NaCl (n = 7), cremophor (vehicle for Cy A: n = 7) and 30 mg/kg b.w. Cy A in cremophor (n = 7) daily for 4 weeks. METHODS: Oxidized (GSSG) and reduced (GSH) glutathione, lipid peroxides and superoxide dismutase were measured in the organs. RESULTS: Increases in GSSG [nmol/mg prot.] and a compensatory rise in total GSH [nmol/mg prot.] indicating Cy A-induced oxidative stress were found in kidney (0.39 +/- 0.09 vs. 0.47 +/- 0.14 vs. 0.64 +/- 0.18; 20.71 +/- 3.86 vs. 21.07 +/- 3.86 vs. 28.14 +/- 3.37) and liver (0.51 +/- 0.11 vs. 0.51 +/- 0.09 vs. 0.65 +/- 0.25; 33.35 +/- 5.06 vs. 32.88 +/- 5.12 vs. 44.12 +/- 6.06) but not in heart. CONCLUSION: Cy A-induced oxidative stress may contribute to the hepatotoxicity and nephrotoxicity of this drug. After heart transplantation, accelerated allograft atherosclerosis limits transplantation success. We did not find any evidence that Cy A induces oxidative stress in the heart which might favour atherogenesis.

Animals↗

PubMed1997

Intracellular metabolism of 4-hydroxynonenal in primary cultures of rabbit synovial fibroblasts.

The intracellular metabolism of 4-hydroxynonenal (HNE), a secondary product of lipid peroxidation and mediator of inflammation, which was found in the joints of patients with rheumatoid arthritis, was investigated in primary cultures of rabbit synovial fibroblasts. A consumption rate of 27.3 nmol/min x 10(6) cells was measured for the cultivated fibroblasts. It could be shown, that 4-hydroxynonenal enters the synovial fibroblasts and is metabolized mainly oxidatively to 4-hydroxynonenoic acid, intermediates of the tricarboxylic acid cycle and water and by formation of the glutathione-HNE adduct. The share of protein-bound HNE was about up to 8% of the total added HNE after 10 min of incubation. All metabolites accumulates intracellularly within the incubation time except of 4-hydroxynonenal itself. An increase of 4-hydroxynonenoic acid could be detected also extracellularly during the intracellular metabolism of 4-hydroxynonenal. Therefore, an involvement of synovial fibroblasts in the secondary antioxidant defense system of the joints during conditions of higher HNE concentrations like rheumatoid arthritis is suggested.

Aldehydes↗

PubMed1997

Increased levels of 4-hydroxynonenal modified proteins in plasma of children with autoimmune diseases.

Analysis of serum samples of healthy children (n = 11) and children with Systemic Lupus Erythematosus (SLE), (n = 21) was performed by SDS-PAGE and immunoblot with an antibody directed against proteins modified by lipid peroxidation (LPO) product 4-hydroxynonenal (HNE). A single major stained protein band was detected. By comparison of the molecular weights in nonreducing and reducing SDS-PAGE was found that the main protein modified by HNE is immunoglobulin G. Significantly higher concentrations of the aldehyde modified protein were found in children with high disease activity of SLE measured by SLE disease activity index (SLEDAI). Lipid peroxidation measured by malondialdehyde and 4-hydroxynonenal concentrations show an enhanced level of both compounds also in patients with the active autoimmune disease. Therefore, it can be assumed that free radical mediated processes play a pathophysiological role in the active phase of SLE and HNE-modified serum proteins are a further parameter for the detection of in vivo LPO.

Adolescent↗

PubMed1997

Increased lipid peroxidation in children with autoimmune diseases.

To examine the role of oxidative damage in children and adolescents with autoimmune diseases, we compared blood serum levels of the lipid peroxidation (LPO) products 4-hydroxynonenal (HNE) and malondialdehyde (MDA) in 22 children with systemic lupus erythematosus (SLE), 13 children with focal type of scleroderma, and 21 health controls. In order to study the influence of disease activity in SLE on serum LPO product levels, the SLE group was divided into one group with active disease (n = 11) and one group with non-active disease (n = 11) according to SLEDAI-score, 15.1 and 1.8, respectively. SLE patients with active SLE (146 +/- 14 nmol/l, median 145 nmol/l) have significantly higher HNE levels compared to controls (61 +/- 10 nmol/l, median 52 nmol/l), whereas the MDA serum levels are similar to those of the control group, 1.94 +/- 0.18 mumol/l (median: 2.02 mumol/l) and 1.58 +/- 0.11 mumol/l (median: 1.52 mumol/l), respectively. Children with SCL had HNE and MDA levels similar to the control group.

Adolescent↗

PubMed1997

Models for the regulation of purine metabolism in rat hepatocytes: evaluation of tracer kinetic experiments.

Metabolic pathways are characterized by numerous regulatory mechanisms. Their study calls for the determination of the metabolite concentrations as well as the flux rates. Corresponding experiments using purified enzymes and an artificial environment frequently yield results that differ from findings for in vivo systems. To be more realistic, the tracer kinetic experiments presented here involved intact isolated hepatocytes. It is necessary to establish mathematical models to deduce the flux rates. With the presumption of metabolic steady-state conditions, the flux rates are determined by a possibly stiff system of linear differential equations. For the first time, the flux rate determination in the purine metabolism of rat hepatocytes was accomplished by applying a combination of a nonlinear least-square fit and a numerical integration. Because of the complexity of this pathway, it was necessary to use three different tracers requiring three partial models. By ensuring their compatibility and using a fit of high statistical quality, the experimental situation could be described adequately. Our flux rate analysis confirmed earlier experimental findings and also allows much more insight into the regulatory mechanisms of the metabolism studied.

Adenine↗

PubMed1997

Inhibition of NADPH oxidase-mediated superoxide radical formation in PMA-stimulated human neutrophils by 4-hydroxynonenal--binding to -SH and -NH2 groups.

4-Hydroxynonenal (HNE), a major lipid peroxidation product, effectively inhibits the superoxide radical formation by NADPH oxidase of phorbol myristate acetate (PMA)--stimulated human PMNL. The I50 value for the inhibition of NADPH oxidase-mediated superoxide radical formation by 4-hydroxynonenal was found to be 19 microM. The HNE inhibition involves the reaction with both -SH and -NH2 groups. Superoxide formation as final result of the NADPH oxidase cascade was almost completely restored by addition of dithiothreitol. In presence of hydroxylamine only a minor restoration of superoxide radical formation was found. A combination of dithiothreitol and hydroxylamine yielded the greatest recovery. Two other aldehydes with the same chain length as HNE but different binding to lysine, histidine and cysteine residues, trans-2,3-nonenal and nonanal, gave I50 values for the inhibition of NADPH oxidase-mediated superoxide formation rate of 110 microM or > 300 microM, respectively.

Aldehydes↗

PubMed1997

Metabolic fate of 4-hydroxynonenal in hepatocytes: 1,4-dihydroxynonene is not the main product.

4-Hydroxynonenal (HNE) is a major aldehydic product of lipid peroxidation known to exert several biological and cytotoxic effects. The metabolic fate of this aldehyde was investigated in hepatocytes as a cell type with a rapid HNE degradation. The experiments were carried out in rat hepatocytes at 37 degrees C at initial HNE concentrations of 1 microM-that means in the range of physiological and pathophysiologically relevant HNE levels-, 5 microM or 100 microM, respectively. About 95% of 100 microM HNE was degraded within 3 min of incubation. At 1 microM HNE the physiological level of about 0.1 to 0.2 microM was restored already after 30 sec. As primary products of HNE in hepatocytes the glutathione-HNE- 1:1-adduct, the hydroxynonenoic acid and the corresponding alcohol of HNE, the 1,4-dihydroxynon-2-ene, were identified. In contrast to previous reports, the corresponding alcohol of the HNE, 1,4-dihydroxynon-2-ene, was not the main HNE metabolite by far. The sum of these three primary HNE products accounts for about two-thirds of the total HNE degradation after 3 min of incubation. Furthermore, the beta-oxidation of hydroxynonenoic acid including the formation of water was demonstrated. The quantitative share of HNE binding to proteins, contrary to its great functional importance, is low with about 3% of total HNE consumption after 3 min incubation. The glycine-cysteine-HNE, cysteine-HNE adducts, and the mercapturic acid from glutathione-HNE adduct are not formed. In total, almost 90% of HNE degradation could be balanced by the formation of different HNE metabolites. The fast metabolism underlines the role of HNE degrading pathways in hepatocytes as one important part of the antioxidative defense system in order to protect proteins from modification by aldehydic lipid peroxidation products.

Aldehydes↗

PubMed1997

Degradation of oxidized proteins in mammalian cells.

Protein oxidation in vivo is a natural consequence of aerobic life. Oxygen radicals and other activated oxygen species generated as by-products of cellular metabolism or from environmental sources cause modifications to the amino acids of proteins that generally result in loss of protein function/enzymatic activity. Oxidatively modified proteins can undergo direct chemical fragmentation or can form large aggregates due to covalent cross-linking reactions and increased surface hydrophobicity. Mammalian cells exhibit only limited direct repair mechanisms and most oxidized proteins undergo selective proteolysis. The proteasome appears to be largely responsible for the degradation of soluble intracellular proteins. In most cells, oxidized proteins are cleaved in an ATP-and ubiquitin-independent pathway by the 20 S "core" proteasome. The proteasome complex recognizes hydrophobic amino acid residues, aromatic residues, and bulky aliphatic residues that are exposed during the oxidative rearrangement of secondary and tertiary protein structure: increased surface hydrophobicity is a feature common to all oxidized proteins so far tested. The recognition of such (normally shielded) hydrophobic residues is the suggested mechanism by which proteasome catalyzes the selective removal of oxidatively modified cell proteins. By minimizing protein aggregation and cross-linking and by removing potentially toxic protein fragments, proteasome plays a key role in the overall antioxidant defenses that minimize the ravages of aging and disease.

Amino Acids↗

PubMed1997

Identification of metabolic pathways of the lipid peroxidation product 4-hydroxynonenal in in situ perfused rat kidney.

The metabolism of the cytotoxic lipid peroxidation product 4-hydroxynonenal was studied in perfused rat kidney. We investigated the total capacity of the rat kidney to metabolize 4-hydroxynonenal (HNE) and quantified the metabolites in the venous effluents as well as in the excreted urine. A rapid utilization of HNE was demonstrated, due to its immediate reactions with cellular compounds and its metabolism. During the first 3 min more than 80% of the infused HNE was metabolized in the perfused kidney. Glutathione-HNE conjugate (GSH-HNE: 35%), the corresponding alcohol 1,4-dihydroxynonene (1,4-DHN: 12%), HNE-mercapturic acid conjugate (HNE-MA: 4%), 4-hydroxynonenoic acid (HNA: 7%), tricarboxylic acid (TCA-cycle metabolites), and water (32%) were identified as primary and secondary metabolic products. We postulated that the total capacity of rat kidney to metabolize 4-hydroxynonenal with about 160-190 nmol/g wet wt/min. (initial influent concentration was 100 nmol/ml HNE) and other aldehydic products of lipid peroxidation is in the same range as that in other organs, e.g., intestine with 22 nmol/g wet wt/min (initial 70 nmol/ml HNE) (Siems et al. 1995. Life Sci. 57: 785-789) and heart with about 50 nmol/g wet wt/min (initial 10 nmol/ml HNE) (Grune et al. 1994. Cell Biochem. Funct. 12: 143-147). Compared to other organs, liver and kidney seemed to be the most important organs for the elimination of the final products of metabolism. The importance of the kidney in the formation of HNE-mercapturic acid conjugate was demonstrated (Alary et al. 1995. Chem. Res Toxicol. 8: 34-39). The selective excretion of this final metabolite of aldehyde metabolism may be of central importance in the detoxification of a number of lipid peroxidation products.

Aldehydes↗

PubMed1996

High metabolic rates of 4-hydroxynonenal in brain capillary endothelial cells during hypoxia/reoxygenation.

We measured the accumulation of 4-hydroxynonenal (HNE), a major lipid peroxidation product during hypoxia/reoxygenation of brain capillary endothelial cells (BCEC). The concentration of HNE after 2 h of hypoxia was 0.23 nmol/mg protein and rose up to 0.28 nmol/mg protein after 30 min of reoxygenation. That reflects a 1.5-fold increase, whereas aortic endothelial cells (AEC) increased the HNE level 5-fold, compared to the control. Therefore, the ability of BCEC to degrade exogenously added HNE was tested. The HNE consumption in BCEC achieved a rate of about 600 nmol.min-1.mg protein-1, about two times higher than in AEC. The higher ability of BCEC to degrade HNE is probably the reason of the 2-fold higher IC50 value against the aldehyde. Therefore, we concluded that the high ability of BCEC to degrade HNE is a substantial part of the secondary antioxidative defense of the brain.

Aldehydes↗

PubMed1996

Degradation of oxidized proteins in K562 human hematopoietic cells by proteasome.

Exposure to various forms of oxidative stress (H2O2 and O2.-) significantly increased the intracellular degradation of both "short-lived" and "long-lived" cellular proteins in the human hematopoietic cell line K562. Oxidatively modified hemoglobin and superoxide dismutase used as purified proteolytic substrates were also selectively degraded by K562 cell lysates, but exposure of these protein substrates to very high hydrogen peroxide concentrations actually decreased their proteolytic susceptibility. Our studies found little or no change in the overall capacity of cells and cell lysates to degrade "foreign" oxidized proteins after treatment of K562 cells with hydrogen peroxide or paraquat, a finding supported by proteasome Western blots and unchanged capacity of cell lysates to degrade the fluorogenic peptide succinyl-leucine-leucine-valine-tyrosine-4-methylcoumarin-7-amide. Six days of daily treatment of K562 cells with an antisense oligodeoxynucleotide directed against the initiation codon region of the human proteasome C2 subunit gene dramatically depressed hydrogen peroxide-induced degradation of metabolically radiolabeled intracellular proteins. The actual amount of proteasome in antisense-treated K562 cells was also severely depressed, as revealed by Western blots and by measurements of the degradation of the fluorogenic peptide succinyl-leucine-leucine-valine-tyrosine-4-methylcoumarin-7-amide. The degradation of oxidatively modified foreign protein substrates was also markedly depressed in lysates prepared from K562 cells treated with the proteasome C2 antisense dideoxynucleotide. The inhibitor profile for the degradation of H2O2-modified hemoglobin by K562 cell lysates was consistent with a major role for the ATP-independent 20 S "core" proteasome complex. We conclude that proteasome, probably the 20 S core proteasome complex, is primarily responsible for the selective degradation of oxidatively damaged proteins in human hematopoietic cells. Since "oxidative marking" of cellular proteins by lipoxygenase has been proposed as an important step in red blood cell maturation, it is important to determine which protease or proteases could recognize and degrade such modified substrates. Our results provide evidence that proteasome can, indeed, conduct such selective degradation and appears to be the major cellular protease capable of fulfilling such a role in maturation.

Cysteine Endopeptidases↗