Arkansas Children's Nutrition Center, Little Rock, AR 72202, USA.
Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72202, USA.
Int J Mol Sci. 2022 Apr 26;23(9):4747. doi: 10.3390/ijms23094747.
Myoglobin (Mb)-mediated oxygen (O) delivery and dissolved O in the cytosol are two major sources that support oxidative phosphorylation. During intense exercise, lactate (LAC) production is elevated in skeletal muscles as a consequence of insufficient intracellular O supply. The latter results in diminished mitochondrial oxidative metabolism and an increased reliance on nonoxidative pathways to generate ATP. Whether or not metabolites from these pathways impact Mb-O associations remains to be established. In the present study, we employed isothermal titration calorimetry, O kinetic studies, and UV-Vis spectroscopy to evaluate the LAC affinity toward Mb (oxy- and deoxy-Mb) and the effect of LAC on O release from oxy-Mb in varying pH conditions (pH 6.0-7.0). Our results show that LAC avidly binds to both oxy- and deoxy-Mb (only at acidic pH for the latter). Similarly, in the presence of LAC, increased release of O from oxy-Mb was detected. This suggests that with LAC binding to Mb, the structural conformation of the protein (near the heme center) might be altered, which concomitantly triggers the release of O. Taken together, these novel findings support a mechanism where LAC acts as a regulator of O management in Mb-rich tissues and/or influences the putative signaling roles for oxy- and deoxy-Mb, especially under conditions of LAC accumulation and lactic acidosis.
肌红蛋白（Mb）介导的氧（O）输送和细胞质中的溶解 O 是支持氧化磷酸化的两个主要来源。在剧烈运动期间，由于细胞内 O 供应不足，骨骼肌中乳酸（LAC）的产生会升高。后者导致线粒体氧化代谢减少，对生成 ATP 的非氧化途径的依赖增加。这些途径中的代谢产物是否会影响 Mb-O 结合仍有待确定。在本研究中，我们采用等温滴定量热法、O 动力学研究和紫外可见光谱法来评估 LAC 对 Mb（氧合和脱氧 Mb）的亲和力，以及 LAC 在不同 pH 值条件（pH 6.0-7.0）下对氧合 Mb 中 O 释放的影响。我们的结果表明，LAC 强烈结合氧合和脱氧 Mb（仅对后者在酸性 pH 值下）。同样，在存在 LAC 的情况下，检测到从氧合 Mb 中释放出更多的 O。这表明，随着 LAC 与 Mb 结合，蛋白质的结构构象（靠近血红素中心）可能发生改变，这同时触发了 O 的释放。总之，这些新发现支持了一种机制，即 LAC 作为富含 Mb 的组织中 O 管理的调节剂，并且/或者影响氧合和脱氧 Mb 的假定信号作用，特别是在 LAC 积累和乳酸酸中毒的情况下。
