Research School of Biological Sciences, Australian National University, P. O. Box 475, Canberra ACT 2601, Australia.
Plant Physiol. 1990 Aug;93(4):1376-82. doi: 10.1104/pp.93.4.1376.
The catalytic activity of ribulosebisphosphate carboxylase (Rubisco) declined as soon as catalysis was initiated by exposure to its substrate, d-ribulose-1,5-bisphosphate (ribulose-P(2)). The decline continued exponentially, with a half-time of approximately 7 minutes until, eventually, a steady state level of activity was reached which could be as low as 15% of the initial activity. The ratio of the steady state activity to the initial activity was lower at low CO(2) concentration and at low pH. The inhibitors 6-phosphogluconate and H(2)O(2) alleviated the inactivation, increasing the final/initial rate ratio and the half-time. Varying ribulose-P(2) concentration in the range above that required to saturate catalysis did not affect the kinetics of inactivation. The affinities for CO(2) and ribulose-P(2) were unaffected by the inactivation. The decline in activity occurred with preparations of ribulose-P(2) which contained no detectable d-xylulose-1,5-bisphosphate and also with ribulose-P(2) which had been generated enzymatically immediately before use. Inclusion of an aldolase system for removing d-xylulose-1,5-bisphosphate also did not alter the inactivation process. The inactivated Rubisco did not recover after complete exhaustion of ribulose-P(2). We conclude that the inactivation is not caused by readily-reversible binding of ribulose-P(2) at a site different from the active site and that it is unlikely to be attributable to inhibitory contaminants in ribulose-P(2) preparations.
核酮糖-1,5-二磷酸羧化酶（Rubisco）一与底物 d-核酮糖-1,5-二磷酸（核酮糖-P(2)）接触就开始催化，其催化活性随即下降。这种下降呈指数式持续，半衰期约为 7 分钟，直到最终达到一个稳定的活性水平，其活性可能只有初始活性的 15%。在低 CO(2)浓度和低 pH 值下，稳态活性与初始活性的比值较低。抑制剂 6-磷酸葡萄糖酸和 H(2)O(2)可缓解失活，增加最终/初始速率比和半衰期。在高于饱和催化所需浓度范围内改变核酮糖-P(2)浓度不会影响失活动力学。CO(2)和核酮糖-P(2)的亲和力不受失活影响。活性下降发生在含有检测不到的 d-木酮糖-1,5-二磷酸的核酮糖-P(2)制剂中，也发生在使用前酶促生成的核酮糖-P(2)制剂中。加入醛缩酶系统以去除 d-木酮糖-1,5-二磷酸也不会改变失活过程。失活的 Rubisco 在核酮糖-P(2)完全耗尽后不会恢复。我们得出结论，失活不是由于核酮糖-P(2)在不同于活性部位的位点上的可逆结合引起的，而且不太可能归因于核酮糖-P(2)制剂中的抑制性杂质。
