Ashby B, Wernick E, Holmsen H
J Biol Chem. 1983 Jan 10;258(1):321-5.
Thrombin-stimulated platelet secretion is accompanied by a 30% reduction in the steady state level of cytosolic ATP, a breakdown that proceeds through ADP, AMP, IMP, and inosine to hypoxanthine. The ATP to hypoxanthine conversion could be blocked at the stage of AMP deamination by incubation of platelet-rich plasma for 6 h with 200 microM coformycin, a transition-state analog inhibitor of AMP deaminase. Abolition of AMP deaminase activity had no effect on thrombin-induced secretion from the dense granules, alpha-granules, or acid hydrolases measured in gel-filtered platelets. Coformycin treatment had no effect on thrombin-stimulated lactate production, even when oxidative phosphorylation was blocked by antimycin A, nor on the rate of thrombin-stimulated glycogenolysis. In addition, although it was clear that the adenylate energy charge was maintained by activation of AMP deaminase following thrombin treatment, the adenylate energy charge was also maintained in coformycin-treated platelets, albeit after a short lag, by stimulated ATP production and equilibration through the adenylate kinase reaction. Hydrogen peroxide brings about similar adenylate degradation which could also be inhibited by coformycin. The results indicate that AMP deamination and secretion, although temporally related, are not coupled. The role of AMP deaminase appears to be to maintain the adenylate energy charge in the absence of stimulation of ATP production or to buffer the adenylate charge before ATP production is stimulated.
凝血酶刺激的血小板分泌伴随着胞质ATP稳态水平降低30%，这种分解过程通过ADP、AMP、IMP和肌苷直至次黄嘌呤。通过将富含血小板的血浆与200微摩尔的助间型霉素（一种AMP脱氨酶的过渡态类似物抑制剂）孵育6小时，可在AMP脱氨阶段阻断ATP向次黄嘌呤的转化。AMP脱氨酶活性的消除对凝血酶诱导的致密颗粒、α颗粒或在凝胶过滤血小板中测量的酸性水解酶的分泌没有影响。助间型霉素处理对凝血酶刺激的乳酸生成没有影响，即使氧化磷酸化被抗霉素A阻断时也是如此，对凝血酶刺激的糖原分解速率也没有影响。此外，虽然很明显凝血酶处理后通过激活AMP脱氨酶维持腺苷酸能荷，但在助间型霉素处理的血小板中，尽管有短暂延迟，通过刺激ATP生成并通过腺苷酸激酶反应达到平衡，腺苷酸能荷也得以维持。过氧化氢会导致类似的腺苷酸降解，这也可被助间型霉素抑制。结果表明，AMP脱氨和分泌虽然在时间上相关，但并非偶联的。AMP脱氨酶的作用似乎是在不刺激ATP生成的情况下维持腺苷酸能荷，或在刺激ATP生成之前缓冲腺苷酸荷。
