Parra J, Pette D
Fakultät für Biologie, Universität Konstanz, Germany.
Biochim Biophys Acta. 1995 Sep 6;1251(2):154-60. doi: 10.1016/0167-4838(95)00084-8.
Several glycolytic enzymes exist in muscle as free and structure-bound forms. A fraction of hexokinase (HK) is associated with the outer mitochondrial membrane. Phosphofructokinase (PFK) and aldolase (ALD) bind to F-actin, and AMP deaminase (AMPase) interacts with myosin. Using low-frequency stimulation (10 Hz, 24 h/d), we studied in rat fast-twitch muscle effects of contractile activity on soluble and structure-bound forms of these enzymes. Phosphoglucose isomerase (PGI), a soluble enzyme, was also examined. Fractional extraction was applied to study the intracellular distribution of soluble and bound enzyme activities 5 min, 1 h, 3 h, 1 d, and 7 d after the onset of stimulation. Confirming previous findings, total HK activity increased 7-fold in 7-d-stimulated muscles, whereas PFK, ALD, and PGI were reduced, ranging between 55% and 80% of their normal activities. AMPase activity was unaltered. At the time points studied, no changes were found in the extraction behavior of PGI and AMPase. The fraction of bound ALD increased slightly (12%). However, the distribution of HK and PFK was markedly altered. Bound PFK increased from 50% in the control to 85% in 7-d-stimulated muscles. Bound HK rose from 52% to 83% during the same time period. The increase in PFK binding was steep and occurred mainly within the first minutes and hours. The increase in HK binding occurred with some delay, but was significant in muscles stimulated for more than 1 h. In view of the altered kinetic properties of F-actin-bound PFK (alleviated allosteric inhibition by ATP) and bound HK (elevated catalytic activity), these changes are interpreted as early responses to match the metabolic demands during maximal contractile activity imposed on a muscle not programmed for sustained activity: Enhanced binding of PFK serves to accelerate glycolytic flux immediately after the onset of stimulation, whereas mitochondrial binding of HK facilitates the phosphorylation of exogenous glucose when glycogen stores have been depleted.
几种糖酵解酶在肌肉中以游离形式和与结构结合的形式存在。己糖激酶（HK）的一部分与线粒体外膜相关联。磷酸果糖激酶（PFK）和醛缩酶（ALD）与F-肌动蛋白结合，而AMP脱氨酶（AMPase）与肌球蛋白相互作用。我们使用低频刺激（10Hz，每天24小时），研究了大鼠快肌中收缩活动对这些酶的可溶性和与结构结合形式的影响。还检测了可溶性酶磷酸葡萄糖异构酶（PGI）。采用分级提取法研究刺激开始后5分钟、1小时、3小时、1天和7天可溶性和结合酶活性的细胞内分布。证实了先前的研究结果，在刺激7天的肌肉中，总HK活性增加了7倍，而PFK、ALD和PGI降低，降至其正常活性的55%至80%之间。AMPase活性未改变。在所研究的时间点，PGI和AMPase的提取行为未发现变化。结合的ALD比例略有增加（12%）。然而，HK和PFK的分布发生了明显改变。结合的PFK从对照中的50%增加到刺激7天的肌肉中的85%。在同一时期，结合的HK从52%上升到83%。PFK结合的增加很迅速，主要发生在最初的几分钟和几小时内。HK结合的增加有一定延迟，但在刺激超过1小时的肌肉中很显著。鉴于与F-肌动蛋白结合的PFK（ATP对变构抑制的缓解）和结合的HK（催化活性升高）的动力学特性发生改变，这些变化被解释为对肌肉在未进行持续活动编程的情况下施加最大收缩活动期间代谢需求的早期反应：PFK结合的增强有助于在刺激开始后立即加速糖酵解通量，而HK与线粒体的结合在糖原储备耗尽时促进外源葡萄糖的磷酸化。
