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Macrophage oxidation of L-arginine to nitrite and nitrate: nitric oxide is an intermediate 总被引:117,自引:0,他引:117
Previous studies have shown that murine macrophages immunostimulated with interferon gamma and Escherichia coli lipopolysaccharide synthesize NO2-, NO3-, and citrulline from L-arginine by oxidation of one of the two chemically equivalent guanido nitrogens. The enzymatic activity for this very unusual reaction was found in the 100,000g supernatant isolated from activated RAW 264.7 cells and was totally absent in unstimulated cells. This activity requires NADPH and L-arginine and is enhanced by Mg2+. When the subcellular fraction containing the enzyme activity was incubated with L-arginine, NADPH, and Mg2+, the formation of nitric oxide was observed. Nitric oxide formation was dependent on the presence of L-arginine and NADPH and was inhibited by the NO2-/NO3- synthesis inhibitor NG-monomethyl-L-arginine. Furthermore, when incubated with L-[guanido-15N2]arginine, the nitric oxide was 15N-labeled. The results show that nitric oxide is an intermediate in the L-arginine to NO2-, NO3-, and citrulline pathway. L-Arginine is required for the activation of macrophages to the bactericidal/tumoricidal state and suggests that nitric oxide is serving as an intracellular signal for this activation process in a manner similar to that very recently observed in endothelial cells, where nitric oxide leads to vascular smooth muscle relaxation [Palmer, R. M. J., Ashton, D. S., & Moncada, S. (1988) Nature (London) 333, 664-666]. 相似文献
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The antitumor antibiotic netropsin has been co-crystallized with a double-helical B-DNA dodecanucleotide of sequence: C-G-C-G-A-A-T-T-BrC-G-C-G, and the structure of the complex has been solved by X-ray diffraction at a resolution of 2.2 A. The structure has been refined independently by Jack-Levitt and Hendrickson-Konnert least-squares methods, leading to a final residual error of 0.257 by the Jack-Levitt approach (0.211 for two-sigma data) or 0.248 by the Hendrickson-Konnert approach, with no significant difference between refined structures. The netropsin molecule displaces the spine of hydration and fits snugly within the minor groove in the A-A-T-T center. It widens the groove slightly and bends the helix axis back by 8 degrees, but neither unwinds nor elongates the double helix. The drug molecule is held in place by amide NH hydrogen bonds that bridge adenine N-3 and thymine O-2 atoms, exactly as with the spine of hydration. The requirement of A X T base-pairs in the binding site arises because the N-2 amino group of guanine would demand impermissibly close contacts with netropsin. It is proposed that substitution of imidazole for pyrrole in netropsin should create a family of "lexitropsins" capable of reading G X C-containing base sequences. 相似文献
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Summary A brief review is presented of the Vester-Ulbricht -decay Bremsstrahlen hypothesis for the origin of optical activity, and of subsequent experiments designed to test it. Certain of our experiments along these lines, begun in 1974 and involving the irradiation of racemic and optically active amino acids in a 61.7 KCi90Sr–90Y Bremsstrahlen source, have now been completed and are described. After 10.89 years of irradiation with a total Bremsstrahlen dose of 2.5×109 rads, crystallinedl-leucine, norleucine, and norvaline suffered 47.2, 33.6, and 27.4% radiolysis, respectively, but showed no evidence whatsoever of asymmetric degradation.d- andl-Leucine underwent about 48% radiolysis and showed 2.4–2.9% radioracemization. Other samples in solution were too severely degraded to analyze. Probable intrinsic reasons for the failure of the Vester-Ulbricht mechanism to afford asymmetric radiolysis in the present and related experiments involving -decay Bremsstrahlen are enumerated.A portion of this material was presented at the 7th International Conference on the Origins of Life, Mainz, FRG, July 10–15, 1983 相似文献
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Reduced synthesis of basement membrane heparan sulfate proteoglycan in streptozotocin-induced diabetic mice 总被引:4,自引:0,他引:4
D H Rohrbach C W Wagner V L Star G R Martin K S Brown J W Yoon 《The Journal of biological chemistry》1983,258(19):11672-11677
In diabetes, certain basement membranes become thicker yet more porous than normal. To identify possible changes in the basement membrane, we have grown the Engelbreth-Holm-Swarm tumor, a tissue that produces quantities of basement membrane in normal mice and in streptozotocin-treated, insulin-deficient, diabetic mice. The level of laminin, a basement membrane-specific glycoprotein, and the level of total protein were slightly elevated in the diabetic tissue. In contrast, the level of the basement membrane specific heparan sulfate proteoglycan was only 20% of control. The synthesis of this proteoglycan was also reduced in the diabetic animals, while the synthesis of other proteoglycans by tissues such as cartilage was normal. The synthesis of the heparan sulfate proteoglycan in diabetic animals was inversely related to plasma glucose levels showing an abrupt decrease above the normal range of plasma glucose. Insulin restored synthesis to normal but this required doses of insulin that maintained plasma glucose at normal levels for several hours. Since the heparan sulfate proteoglycan in the basement membrane restricts passage of proteins, its absence could account for the increased porosity of basement membrane in diabetes. A compensatory synthesis of other components could lead to their increased deposition and the accumulation of basement membrane in diabetes. 相似文献
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Reduced glutathione (GSH) inhibited catalase activity in a dose-dependent manner. DL-dithiothreitol (DL-DTT) and dithioerythritol (DTE) also inhibited catalase activity. The inhibition of catalase by GSH and DL-DTT could be reduced by NADPH. Polyacrilamide gel electrophoresis demonstrated the inhibition was partially reversible. The inhibition of catalase by GSH appeared to be partly due to superoxide radicals, since it was inhibited by active manganese superoxide dismutase, but not by heat-inactivated enzyme. Other chemical species also appear to take part in the inhibition, but they could not be identified. 相似文献