Coenzyme Specificity of Enzymes in the Oxidative Pentose Phosphate Pathway of Gluconobacter oxydans

The coenzyme specificity of enzymes in the oxidative pentose phosphate pathway of Gluconobacter oxydans was investigated. By investigation of the activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) in the soluble fraction of G. oxydans, and cloning and expression of genes in Escherichia coli, it was found that both G6PDH and 6PGDH have NAD/NADP dual coenzyme specificities. It was suggested that the pentose phosphate pathway is responsible for NADH regeneration in G. oxydans.     

Consumption of NADPH for 2-HG Synthesis Increases Pentose Phosphate Pathway Flux and Sensitizes Cells to Oxidative Stress

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Assessment of the Role of the Glutathione and Pentose Phosphate Pathways in the Protection of Primary Cerebrocortical Cultures from Oxidative Stress

Abstract: Reactive oxygen species have been implicated in neuronal injury associated with various neuropathological disorders. However, little is known regarding the relationship between antioxidant enzyme capacity and resultant toxicity. The antioxidant pathways of primary cerebrocortical cultures were directly examined using a novel technique that measures pentose phosphate pathway (PPP) activity, which is enzymatically coupled to glutathione peroxidase (GPx) detoxification of hydrogen peroxide (H₂O₂). PPP activity was quantified from data obtained by gas chromatography/mass spectrometry analysis of released labeled lactate following metabolic degradation of [1,6-¹³C₂,6,6-²H₂]glucose by cerebrocortical cultures. The antioxidant capacity of these cultures was systematically evaluated using H₂O₂, and the resultant toxicity was quantified by lactate dehydrogenase release. Exposure of primary mixed and purified astrocytic cultures to H₂O₂ caused stimulation of PPP activity in a concentration-dependent fashion from 0.25 to 22.2% and from 6.9 to 66.7% of glucose metabolized to lactate through the PPP, respectively. In the mixed cultures, chelation of iron before H₂O₂ exposure was protective and resulted in a correlation between PPP saturation and toxicity. Conversely, addition of iron, inhibition of GPx, or depletion of glutathione decreased H₂O₂-induced PPP stimulation and increased toxicity. These results implicate the Fenton reaction, reflect the pivotal role of GPx in H₂O₂ detoxification, and contribute to our understanding of the etiological role of free radicals in neuropathological conditions.     

A Metabolic Shift toward Pentose Phosphate Pathway Is Necessary for Amyloid Fibril- and Phorbol 12-Myristate 13-Acetate-induced Neutrophil Extracellular Trap (NET) Formation

Neutrophils are the main defense cells of the innate immune system. Upon stimulation, neutrophils release their chromosomal DNA to trap and kill microorganisms and inhibit their dissemination. These chromatin traps are termed neutrophil extracellular traps (NETs) and are decorated with granular and cytoplasm proteins. NET release can be induced by several microorganism membrane components, phorbol 12-myristate 13-acetate as well as by amyloid fibrils, insoluble proteinaceous molecules associated with more than 40 different pathologies among other stimuli. The intracellular signaling involved in NET formation is complex and remains unclear for most tested stimuli. Herein we demonstrate that a metabolic shift toward the pentose phosphate pathway (PPP) is necessary for NET release because glucose-6-phosphate dehydrogenase (G6PD), an important enzyme from PPP, fuels NADPH oxidase with NADPH to produce superoxide and thus induce NETs. In addition, we observed that mitochondrial reactive oxygen species, which are NADPH-independent, are not effective in producing NETs. These data shed new light on how the PPP and glucose metabolism contributes to NET formation.     

Activation of γ-Aminobutyrate Production by Chloroplastic H2O2 Is Associated with the Oxidative Stress Response

A series of N-substituted aryl and alkyl carbamates (RNHCOOR′; R: aryl, alkyl; R′: aryl, alkyl) was prepared and screened for inhibitory activity toward the germination of oat seeds. The activity of each compound was compared with that of chlorpropham (isopropyl 3-chlorocarbanilate). Some of the synthetic carbamates possessing the N-(phenylthio)methyl group, PhSCH₂NHCOOR´, showed inhibitory activity close or comparable to that of chlorpropham.     

Pentose phosphate pathway,glutathione-dependent enzymes and antioxidant defense during oxidative stress in diabetic rodent brain and peripheral organs: effects of stobadine and vitamin E

The aim of the present study was to investigate the effects of treatment with antioxidant stobadine (ST) on the activities of enzymes related with pentose phosphate pathway and glutathione-dependent metabolism and the other markers of oxidative stress in brain and peripheral organs of diabetic rats, and to compare the effects of ST treatment alone with the effects of treatments with another antioxidant vitamin E and ST plus vitamin E. Rats were made diabetic by the injection of streptozotocin (STZ; 55 mg/kg IP), and, 2 days later, some control and diabetic rats were left untreated or treated with ST (24.7 mg/kg/day, orally), vitamin E (400–500 U/kg/day, orally), or both substances together. In the brain, although 6-phosphogluconate dehydrogenase activity (6-PGD) did not change, glucose-6-phosphate dehydrogenase activity (G-6PD) was markedly increased in diabetic rats compared with controls; only combined treatment with ST and vitamin E produced a partial prevention on this alteration. The aorta G-6PD and 6-PGD of diabetic rats were 52% and 36% of control values, respectively. Neither single treatments with each antioxidant nor their combination altered the G-6PD and 6-PGD in aorta of diabetic rats. Glutathione peroxidase (GSHPx) activity was increased by STZ-diabetes in brain, heart, and kidney. In diabetic brain, vitamin E alone or combination with ST kept GSHPx at normal levels. Diabetes-induced stimulation in GSHPx did not decrease in response to the treatment with vitamin E in heart and kidney, but was greatly prevented by ST alone. The activity of glutathione reductase (GR) was decreased in brain and heart of diabetic rats. The treatment with each antioxidant or with a combination of both agents completely prevented this deficiency and resulted in further activation of GR in diabetic tissues. Glutathione S-transferase (GST) activity did not significantly change in diabetic brain and aorta. GST was stimulated by all treatment protocols in the brain of diabetic rats and was depressed in aorta of control rats. Catalase (CAT) was activated in diabetic heart but depressed in diabetic kidney. Diabetes-induced abnormalities in CAT activity did not respond to vitamin E alone in heart, was moderately ameliorated by the treatment with this vitamin in kidney, and was completely prevented by ST alone in both tissues. Superoxide dismutase (SOD) activity of brain and heart was unchanged by the diabetes but inhibited in diabetic kidney after the treatment ST alone or ST plus vitamin E. The lipid peroxidation (MDA) was increased in diabetic brain and heart. ST or vitamin E alone partly prevented diabetes-induced increase in MDA in brain and heart; however, antioxidant combination achieved a completely amelioration in MDA of these tissues of diabetic rats. Kidney MDA levels were similar in control and untreated diabetic animals. ST and vitamin E treatments, when applied separately or together, significantly reduced kidney MDA in both control and diabetic rats; and the combined effect of antioxidants was greater than that of each alone. These results are consistent with the degenerative role of hyperglycemia on cellular reducing equivalent homeostasis and antioxidant defense, and provide further evidence that pharmacological intervention of different antioxidants may have significant implications in the prevention of the prooxidant feature of diabetes and protects redox status of the cells.     

Oxidative stress in the aging substantia nigra and the etiology of Parkinson's disease

Parkinson's disease prevalence is rapidly increasing in an aging global population. With this increase comes exponentially rising social and economic costs, emphasizing the immediate need for effective disease‐modifying treatments. Motor dysfunction results from the loss of dopaminergic neurons in the substantia nigra pars compacta and depletion of dopamine in the nigrostriatal pathway. While a specific biochemical mechanism remains elusive, oxidative stress plays an undeniable role in a complex and progressive neurodegenerative cascade. This review will explore the molecular factors that contribute to the high steady‐state of oxidative stress in the healthy substantia nigra during aging, and how this chemical environment renders neurons susceptible to oxidative damage in Parkinson's disease. Contributing factors to oxidative stress during aging and as a pathogenic mechanism for Parkinson's disease will be discussed within the context of how and why therapeutic approaches targeting cellular redox activity in this disorder have, to date, yielded little therapeutic benefit. We present a contemporary perspective on the central biochemical contribution of redox imbalance to Parkinson's disease etiology and argue that improving our ability to accurately measure oxidative stress, dopaminergic neurotransmission and cell death pathways in vivo is crucial for both the development of new therapies and the identification of novel disease biomarkers.     

Oxidative shielding and the cost of reproduction

Life‐history theory assumes that reproduction and lifespan are constrained by trade‐offs which prevent their simultaneous increase. Recently, there has been considerable interest in the possibility that this cost of reproduction is mediated by oxidative stress. However, empirical tests of this theory have yielded equivocal support. We carried out a meta‐analysis to examine associations between reproduction and oxidative damage across markers and tissues. We show that oxidative damage is positively associated with reproductive effort across females of various species. Yet paradoxically, categorical comparisons of breeders versus non‐breeders reveal that transition to the reproductive state is associated with a step‐change reduction in oxidative damage in certain tissues and markers. Developing offspring may be particularly sensitive to harm caused by oxidative damage in mothers. Therefore, such reductions could potentially function to shield reproducing mothers, gametes and developing offspring from oxidative insults that inevitably increase as a consequence of reproductive effort. According to this perspective, we hypothesise that the cost of reproduction is mediated by dual impacts of maternally‐derived oxidative damage on mothers and offspring, and that mothers may be selected to diminish such damage. Such oxidative shielding may explain why many existing studies have concluded that reproduction has little or no oxidative cost. Future advance in life‐history theory therefore needs to take account of potential transgenerational impacts of the mechanisms underlying life‐history trade‐offs.     

Roles of sirtuins in the regulation of antioxidant defense and bioenergetic function of mitochondria under oxidative stress

Abstract

In addition to serving as the power house of mammalian cells, mitochondria are crucial for the maintenance of cellular homeostasis in response to physiological or environmental changes. Several lines of evidence suggest that posttranslational modification (PTM) of proteins plays a pivotal role in the regulation of the bioenergetic function of mitochondria. Among them, reversible lysine acetylation of mitochondrial proteins has been established as one of the key mechanisms in cellular response to energy demand by modulating the flux of a number of key metabolic pathways. In this article, we focus on the role of Sirt3-mediated deacetylation in: (1) flexibility of energy metabolism, (2) activation of antioxidant defense, and (3) maintenance of cellular redox status in response to dietary challenge and oxidative stress. We suggest that oxidative stress-elicited down-regulation of Sirt3 plays a role in the pathophysiology of diabetes, cardiac hypotrophy, mitochondrial diseases, and age-related diseases. Besides, the physiological role of newly identified lysine acylation mediated by Sirt5 and its biochemical effects on oxidative metabolism are also discussed. Moreover, we have integrated the regulatory function of several protein kinases that are involved in the phosphorylation of mitochondrial enzymes during oxidative stress. Finally, the functional consequence of the synergistic regulation through diverse protein modifications is emphasized on the maintenance of the bioenergetic homeostasis and metabolic adaptation of the animal and human cells. Together, we have provided an updated review of PTM in mitochondrial biology and their implications in aging and human diseases through an intricate regulation of energy metabolism under oxidative stress.     

一氧化氮对盐胁迫下小麦幼苗根生长和氧化损伤的影响

0.05和0.10 mmol/L一氧化氮(NO)供体硝普钠(sodium mtropmsside,SNP)处理明显减轻NaCl浓度为150 mmo1/L左右的盐胁迫对小麦幼苗根生长的抑制效应,其中0.05mmol/L的SNP效果最明显;0.30mmol/L以上的SNP处理对根抑制无明显缓解作用;当NaCl浓度大于300 mmol/L时,各种浓度的SNP均不能减轻盐胁迫对根生长的抑制.以N O清除剂血红蛋白(hemoglobin,Hb)以及NOx-,K3Fe(CN)6等为对照,观察到0.05 mmol/L的SNP能不同程度地提高150mmo/L盐胁迫下小麦幼苗根尖细胞中超氧化物歧化酶(SOD)、过氧化物酶(POD)和抗坏血酸过氧化物酶(ascorbateperoxidase,APX)活性,明显降低MDA、H2O2和O2-.的积累,阻断盐胁迫诱导的根尖细胞DNA片段化,表明NO能有效缓解盐胁迫引起的小麦幼苗根尖细胞的氧化损伤.     

Oxidative Stress and Antioxidant Responses in Young Leaves of Mulberry Plants Grown Under Nitrogen, Phosphorus or Potassium Deficiency

The aim of this study was to associate the generation of reactive oxygen species （ROS） with Induced antloxidant responses and disturbed cellular redox environment in the nitrogen-（N）, phosphorus-（P）, or potassium-（K） deftcient mulberry （Morus alba L. var. Kanva-2） plants. The indicators of oxidative stress and cellular redox environment and antioxldant defense-related parameters were analyzed. Oeficlency of N, P or K suppressed growth, accelerated senescence, and decreased concentrations of chloroplastic pigments and glutathione. Lipid peroxidation and activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase were also increased in these N, P, or K deprived plants. Concentration of hydrogen peroxide Increased in plants deficient in N or P. Oeficlency of N or P particularly altered the cellular redox environment as indicated by changes in the redox couples, namely ascorbic acid/total ascorbate decreased in P-, glutathione sulfydryl/total glutathione decreased in N-, and Increased in P-deficient plants. Activity staining of native gels for superoxide dismutase revealed Increased activity as Indicated by Increased intensity of bands, and induction of few new isoforms in P- and K-deficient plants. Oifferences in the patterns of superoxide dismutase isoforms and redox status （ascorbic acid/total ascorbate and glutathlone sulfydryl/total glutathione） Indicate that N-, P-, or K-deficiency altered antioxidant responses to varying extents in mulberry plants.     

Salicylic Acid Application Mitigates Oxidative Damage and Improves the Growth Performance of Barley under Drought Stress

Drought is a severe environmental constraint, causing a significant reduction in crop productivity across the world. Salicylic acid (SA) is an important plant growth regulator that helps plants cope with the adverse effects induced by various abiotic stresses. The current study investigated the potential effects of SA on drought tolerance efficacy in two barley (Hordeum vulgare) genotypes, namely BARI barley 5 and BARI barley 7. Ten-day-old barley seedlings were exposed to drought stress by maintaining 7.5% soil moisture content in the absence or presence of 0.5, 1.0 and 1.5 mM SA. Drought exposure led to severe damage to both genotypes, as indicated by phenotypic aberrations and reduction of dry biomass. On the other hand, the application of SA to drought-stressed plants protected both barley genotypes from the adverse effects of drought, which was reflected in the improvement of phenotypes and biomass production. SA supplementation improved relative water content and proline levels in drought-stressed barley genotypes, indicating the osmotic adjustment functions of SA under water-deficit conditions. Drought stress induced the accumulation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide (O₂ ^•− ), and the lipid peroxidation product malondialdehyde (MDA) in the leaves of barley plants. Exogenous supply of SA reduced oxidative damage by restricting the accumulation of ROS through the stimulation of the activities of key antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX). Among the three-applied concentrations of SA, 0.5 mM SA exhibited better mitigating effects against drought stress considering the phenotypic performance and biochemical data. Furthermore, BARI barley 5 showed better performance under drought stress than BARI barley 7 in the presence of SA application. Collectively, our results suggest that SA played a crucial role in improving water status and antioxidant defense strategy to protect barley plants from the deleterious effects of water deficiency.     

Analysis of catalase mutants underscores the essential role of CATALASE2 for plant growth and day length‐dependent oxidative signalling

Three genes encode catalase in Arabidopsis. Although the role of CAT2 in photorespiration is well established, the importance of the different catalases in other processes is less clear. Analysis of cat1, cat2, cat3, cat1 cat2, and cat2 cat3 T‐DNA mutants revealed that cat2 had the largest effect on activity in both roots and leaves. Root growth was inhibited in all cat2‐containing lines, but this inhibition was prevented by growing plants at high CO₂, suggesting that it is mainly an indirect effect of stress at the leaf level. Analysis of double mutants suggested some overlap between CAT2 and CAT3 functions in leaves and CAT1 and CAT2 in seeds. When plants had been grown to a similar developmental stage in short days or long days, equal‐time exposure to oxidative stress caused by genetic or pharmacological inhibition of catalase produced a much stronger induction of H₂O₂ marker genes in short day plants. Together, our data (a) underline the importance of CAT2 in basal H₂O₂ processing in Arabidopsis; (b) suggest that CAT1 and CAT3 are mainly “backup” or stress‐specific enzymes; and (c) establish that day length‐dependent responses to catalase deficiency are independent of the duration of oxidative stress.     

Oxidative stress in biological systems and its relation with pathophysiological functions: the effect of physical activity on cellular redox homeostasis

The body of evidence from the past three decades demonstrates that oxidative stress can be involved in several diseases. This study aims to summarise the current state of knowledge on the association between oxidative stress and the pathogenesis of some characteristic to the biological systems diseases and aging process. This review also presents the effect of physical activity on redox homeostasis. There is strong evidence from studies for participation of reactive oxygen and nitrogen species in pathogenesis of acute and chronic diseases based on animal models and human studies. Elevated levels of pro-oxidants and various markers of the oxidative stress and cells and tissues damage linked with pathogenesis of cancer, atherosclerosis, neurodegenerative diseases hypertension, diabetes mellitus, cardiovascular disease, atherosclerosis, reproductive system diseases, and aging were reported. Evidence confirmed that inflammation contributes widely to multiple chronic diseases and is closely linked with oxidative stress. Regular moderate physical activity regulates oxidative stress enhancing cellular antioxidant defence mechanisms, whereas acute exercise not preceded by training can alter cellular redox homeostasis towards higher level of oxidative stress. Future studies are needed to clarify the multifaceted effects of reactive oxygen/nitrogen species on cells and tissues and to continue study on the biochemical roles of antioxidants and physical activity in prevention of oxidative stress-related tissue injury.     

The overexpression of NADPH-producing enzymes counters the oxidative stress evoked by gallium,an iron mimetic

Gallium (Ga), an iron (Fe) mimetic promoted an oxidative environment and elicited an antioxidative response in Pseudomonas fluorescens. Ga-stressed P. fluorescens was characterized by higher amounts of oxidized lipids and proteins compared to control cells. The oxidative environment provoked by Ga was nullified by increased synthesis of NADPH. The activity and expression glucose 6-phosphate dehydrogenase (G6PDH) and isocitrate dehydrogenase-NADP (ICDH) were stimulated in Ga-cultures. The induction of isoenzymes of these dehydrogenases was also evident in the Ga-stressed cells. Although superoxide dismutase (SOD) activity was significantly enhanced in Ga-stressed cultures, catalase activity experienced a marked diminution. Fe metabolism appeared to be severely impeded by Ga toxicity. This is the first demonstration of the oxidative stress evoked by Ga to be neutralized by a reductive environment generated via the overexpression of NADPH-producing enzymes.     

Oxidative stress as regulatory factor for fatty-acid-induced uncoupling involving liver mitochondrial ADP/ATP and aspartate/glutamate antiporters of old rats

Palmitate-induced uncoupling, which involves ADP/ATP and aspartate/glutamate antiporters, has been studied in liver mitochondria of old rats (22-26 months) under conditions of lipid peroxidation and inhibition of oxidative stress by antioxidants--thiourea, Trolox, and ionol. It has been shown that in liver mitochondria of old rats in the absence of antioxidants and under conditions of overproduction of conjugated dienes, the protonophoric uncoupling activity of palmitate is not suppressed by either carboxyatractylate or aspartate used separately. However, the combination of carboxyatractylate and aspartate decreased uncoupling activity of palmitate by 81%. In this case, palmitate-induced uncoupling is limited by a stage insensitive to both carboxyatractylate and aspartate. In the presence of antioxidants, the palmitate-induced protonophoric uncoupling activity is suppressed by either carboxyatractylate or aspartate used separately. Under these conditions, palmitate-induced uncoupling is limited by a stage sensitive to carboxyatractylate (ADP/ATP antiporter) or aspartate (aspartate/glutamate antiporter). In the absence of antioxidants, the uncoupling activity of palmitate is not suppressed by ADP either in the absence or in the presence of aspartate. However, in the presence of thiourea, Trolox, or ionol ADP decreased the uncoupling activity of palmitate by 38%. It is concluded that in liver mitochondria of old rats the development of oxidative stress in the presence of physiological substrates of ADP/ATP and aspartate/glutamate antiporters (ADP and aspartate) results in an increase of the protonophoric uncoupling activity of palmitate.     

Oxidative Stress and Mechanisms of Protection Against It in Bacteria

In the review contemporary data on the effects of oxidative stresses of various kinds in bacteria are summarized. A general theory of oxidative stress, peculiarities of oxidative stress in eukaryotes and prokaryotes, and natural and induced oxidative stresses are described. Data on the mechanisms of protection against oxidative stress are given, including prevention of the generation of oxidative stress, prevention of propagation of free radical chain reactions, and the mechanisms of repair of damaged DNA. The regulation of effector genes via redox-sensitive iron-containing proteins is analyzed. Special attention is given to the expression of so-called antioxidant and associated enzymes as protection mechanisms and to the space–time organization of the response of bacteria to oxidative stress.     

Increased Plasma Manganese, Partially Reduced Ascorbate,1 and Absence of Mitochondrial Oxidative Stress in Type 2 Diabetes Mellitus: Implications for the Superoxide Uncoupling Protein 2 (Ucp-2) Pathway

Oxidative stress is an important component of diabetes and its complications. Manganese (Mn), the key component of the Mitochondrial antioxidant (MnSOD), plays a key role in the superoxide uncoupling protein 2 (UCP-2) pathway in inhibiting of glucose-stimulated insulin secretion (GSIS). The interactions of Mn with ascorbate and other components of this pathway have not been defined in type-2 diabetes. Fifty established type 2 diabetics (30 males, 20 females) and 30 non-diabetics (controls; 18 males, 12 females) matched for age and sex were investigated. Dietary intake, particularly of micronutrients as assessed by 24-h dietary recall was similar between diabetics and controls. Weight and height of all subjects were determined and body mass index (BMI) computed after clinical assessment. Fasting plasma glucose, manganese, ascorbic acid, creatinine and K⁺ levels were determined; K⁺ was to assess the K⁺ channels, whereas creatinine was to assess probability of oxidative stress nephropathy. Body mass index was greater in DM than in controls (p < 0.001). Fasting plasma glucose and Mn levels (p < 0.00 and p < 0.01, respectively) were higher in diabetes than in the controls. Manganese level was greater than twice the levels in controls. Ascorbic acid was not significantly different (p > 0.05), but was 50% lower than the level in non-diabetics. Potassium like Mn and glucose was significantly higher in diabetes mellitus (DM) than in controls (p < 0.001). Creatinine was not significantly different between diabetics and controls (p > 0.05). Correlations among all parameters were not significantly different. These findings suggest absence of significant oxidative stress in the mitochondria, probably excluding a role for UCP-2-superoxide pathway in the inhibition of glucose-stimulated insulin secretion (GSIS), calling for caution in the precocious conclusion that interruption of UCP-2 activity may provide a viable strategy to improve β-cell dysfunction in type 2 diabetes mellitus.     

Deciphering the potential involvement of PXMP2 and PEX11B in hydrogen peroxide permeation across the peroxisomal membrane reveals a role for PEX11B in protein sorting

Peroxisomes have the intrinsic ability to produce and scavenge hydrogen peroxide (H₂O₂), a diffusible second messenger that controls diverse cellular processes by modulating protein activity through cysteine oxidation. Current evidence indicates that H₂O₂, a molecule whose physicochemical properties are similar to those of water, traverses cellular membranes through specific aquaporin channels, called peroxiporins. Until now, no peroxiporin-like proteins have been identified in the peroxisomal membrane, and it is widely assumed that small molecules such as H₂O₂ can freely permeate this membrane through PXMP2, a non-selective pore-forming protein with an upper molecular size limit of 300–600 Da. By employing the CRISPR-Cas9 technology in combination with a Flp-In T-REx 293 cell line that can be used to selectively generate H₂O₂ inside peroxisomes in a controlled manner, we provide evidence that PXMP2 is not essential for H₂O₂ permeation across the peroxisomal membrane, neither in control cells nor in cells lacking PEX11B, a peroxisomal membrane-shaping protein whose yeast homologue facilitates the permeation of molecules up to 400 Da. During the course of this study, we unexpectedly noted that inactivation of PEX11B leads to partial localization of both peroxisomal membrane and matrix proteins to mitochondria and a decrease in peroxisome density. These findings are discussed in terms of the formation of a functional peroxisomal matrix protein import machinery in the outer mitochondrial membrane.