PubMed · 8753216
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M Ikemoto. 1995. [Arginase].. https://pubmed.ncbi.nlm.nih.gov/8753216/
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Chronic venous ulcers, an example of abnormal wound healing, show chronic inflammation with defective matrix deposition which together with the underlying vascular pathology, result in delayed healing. L-arginine is known to be metabolized by one of two pathways: nitric oxide synthase (NOS), producing nitric oxide (NO), or arginase, producing ornithine. NO is involved in many pathological conditions including vascular and inflammatory disorders. This study therefore investigated the distribution, level and activity of NOS and arginase in chronic venous ulcers in comparison with normal skin, using immunocytochemistry, western blotting, and enzyme assays. The results demonstrated an increased distribution of both NOS and arginase in chronic venous ulcer tissue compared with normal skin, with inflammatory cells and vascular endothelial cells as the main sources. These data were confirmed by western blot analysis, which showed increased levels of both enzymes in chronic venous ulcers. Moreover, there was significantly increased activity of both total NOS (p<0.04) and inducible NOS (p<0.05) in chronic venous ulcer tissue compared with normal skin, and significantly increased activity of arginase (p<0.01) in chronic venous ulcer tissue in comparison with normal skin. NO is known to combine with hydroxyl free radicals forming peroxynitrite, a potent free radical which causes tissue destruction. NO overexpression in chronic venous ulcers may be involved directly or indirectly (through production of peroxynitrite) in the pathogenesis and delayed healing of chronic venous ulcers, through its effects on vasculature, inflammation, and collagen deposition. Arginase is known to enhance matrix deposition. Thus, increased levels of arginase in chronic venous ulcers could contribute to the pathogenesis of lipodermatosclerosis associated with chronic venous insufficiency, predisposing to the formation of chronic venous ulcers and also to matrix cuff formation around blood vessels.
Human red blood cells (RBCs) are considered to play a significant role in both blood pressure (BP) regulation and tissue oxygenation, because they can bind as well as release previously bound nitric oxide (NO) from hemoglobin (Hb) and other intracellular components. Two reports indicate that the human RBC possesses nitric oxide synthase (NOS) activity-by the accumulation of nitrite across a membraned chamber in one and by the hydrolysis of labeled L-arginine, presumably to labeled L-citrulline, in the other. Furthermore, NOS proteins have been identified by immunoblot in RBCs. If true, the presence of NOS activity would convert the human RBC to a donor with limited ability to bind exogenously generated NO. In considering the importance of the question of the presence or not of NO synthetic capacity of this cell in BP regulation and tissue perfusion, whether human RBCs are, indeed, able to hydrolyze L-arginine to L-citrulline, the coproduct of NO was explored. RBC samples collected from control subjects were assayed for NOS activity by incubation of homogenized cellular fractions with labeled tritiated L-arginine in the presence of 0.5 mmol/L NADPH. By this method, the amino acid coproduct of NO, tritiated L-citrulline, would be recovered in the supernatant after removal of unused substrate by cationic resin treatment. At first, activity appeared to be present in the RBC supernatant but not in the pellet. However, activity was not suppressed by known inhibitors of NOS, whereas activity was suppressed by norvaline, an inhibitor of arginase activity with no known effect on NOS. By contrast, RBC arginase activity was not inhibited by N(omega)-nitro-L-arginine, NG-methyl-L-arginine, or aminoguanidine, known inhibitors of NOS, but was inhibited by norvaline. The label recovered by thin-layer chromatography was determined not to be tritiated L-citrulline but was instead tritiated L-ornithine, the product of arginase activity. Thus the enzymatic hydrolysis of L-arginine was not caused by NOS but was a result of the action of the enzyme arginase, which abounds in this cell. However, proteins interacting with antibodies to the endothelial and inducible isoforms of NOS were detected in human RBCs by immunoblot. Together, these findings indicate that human RBCs collected from normal adult individuals possess proteins that react with monoclonal antibodies to the Inducible and endothelial isoforms of NOS, but the proteins are without catalytic activity.
The products of three genes named CARGRI, CARGRII, and CARGRIII were shown to repress the expression of CAR1 and CAR2 genes, involved in arginine catabolism. CARGRI is identical to UME6 and encodes a regulator of early meiotic genes. In this work we identify CARGRII as SIN3 and CARGRIII as RPD3. The associated gene products are components of a high-molecular-weight complex with histone deacetylase activity and are recruited by Ume6 to promoters containing a URS1 sequence. Sap30, another component of this complex, is also required to repress CAR1 expression. This histone deacetylase complex prevents the synthesis of the two arginine catabolic enzymes, arginase (CAR1) and ornithine transaminase (CAR2), as long as exogenous nitrogen is available. Upon nitrogen depletion, repression at URS1 is released and Ume6 interacts with ArgRI and ArgRII, two proteins involved in arginine-dependent activation of CAR1 and CAR2, leading to high levels of the two catabolic enzymes despite a low cytosolic arginine pool. Our data also show that the deletion of the UME6 gene impairs cell growth more strongly than the deletion of the SIN3 or RPD3 gene, especially in the Sigma1278b background.