This study aimed to clarify the mechanisms contributing to ontogenetic differences in red locomotor muscle metabolic heat production in regionally endothermic tunas. To address this, the scaling of citrate synthase (CS), cytochrome c oxidase (COX) and pyruvate kinase (PK), enzymes involved in cellular respiration, in the red and white locomotor muscle of young (~ 2 to ~ 16 months of age) Pacific bluefin tuna (Thunnus orientalis) during the ontogeny of red muscle endothermy was investigated. On a mass-specific basis (units g⁻¹ muscle tissue), CS activity scaled negatively with body mass with scaling coefficients of −0.12 for red muscle and −0.21 for white muscle, whereas COX activity did not scale in either muscle type and PK activity scaled positively in white muscle, with a scaling coefficient of 0.09, but did not scale in red muscle. Thus, proxies for mass-specific metabolic heat production potential from cellular respiration either decreased or remained constant in the red muscle during the ontogeny of red muscle endothermy. In contrast, total red muscle mass and total CS and COX activities all scaled positively with body mass, with scaling coefficients of 0.90, 0.78 and 0.92, respectively, and each of these correlated positively with the magnitude of the red muscle thermal excess. Thus, increasing total, but not mass-specific, metabolic heat production capacity contributed to the increasing red muscle thermal excess with increasing body size in juvenile T. orientalis. Additionally, transcript abundance was a poor predictor of enzyme activity. Thus, transcriptional regulation played a limited role in determining the enzymes’ scaling relationships.

本研究旨在阐明导致区域吸热金枪鱼红色运动肌肉代谢产热个体遗传差异的机制。为了解决这个问题，在年轻人（约 2 至约 16 个月大的红白运动肌）中，柠檬酸合酶 (CS)、细胞色素c氧化酶 (COX) 和丙酮酸激酶 (PK) 这些参与细胞呼吸的酶的缩放) 研究了太平洋蓝鳍金枪鱼 ( Thunnus orientalis ) 在红肌吸热个体发育过程中的情况。在特定质量的基础上（单位 g ^-1肌肉组织），CS 活动与体重呈负相关，红肌的比例系数为 -0.12，白肌的比例系数为 -0.21，而 COX 活动在任何一种肌肉类型中都没有比例，PK 活动在白肌中呈正比例，比例系数为0.09，但没有在红肌中缩放。因此，在红肌吸热的个体发育过程中，来自细胞呼吸的质量特异性代谢产热潜力的代理在红肌中降低或保持不变。相比之下，总红肌质量和总 CS 和 COX 活动都与体重成正比，比例系数分别为 0.90、0.78 和 0.92，并且这些系数中的每一个都与红肌热过剩的大小呈正相关。因此，增加总量，但不增加特定质量，T.东方人。此外，转录本丰度是酶活性的不良预测指标。因此，转录调控在确定酶的标度关系方面发挥的作用有限。