Suarez Raul K, Darveau Charles A
Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106-9610, USA.
J Exp Biol. 2005 May;208(Pt 9):1627-34. doi: 10.1242/jeb.01503.
Metabolic control analysis has revealed that flux through pathways is the consequence of system properties, i.e. shared control by multiple steps, as well as the kinetic effects of various pathways and processes over each other. This implies that the allometric scaling of flux rates must be understood in terms of properties that pertain to the regulation of flux rates. In contrast, proponents of models considering the scaling of branching or fractal-like systems suggest that supply rates determine metabolic rates. Therefore, the allometric scaling of supply alone provides a sufficient explanation for the allometric scaling of metabolism. Examination of empirical data from the literature of comparative physiology reveals that basal metabolic rates (BMR) are driven by rates of energy expenditure within internal organs and that the allometric scaling of BMR can be understood in terms of the scaling of the masses and metabolic rates of internal organs. Organ metabolic rates represent the sum of tissue metabolic rates while, within tissues, cellular metabolic rates are the outcome of shared regulation by multiple processes. Maximal metabolic rates (MMR, measured as maximum rates of O2 consumption, VO2max) during exercise also scale allometrically, are also subject to control by multiple processes, but are due mainly to O2 consumption by locomotory muscles. Thus, analyses of the scaling of MMR must consider the scaling of both muscle mass and muscle energy expenditure. Consistent with the principle of symmorphosis, allometry in capacities for supply (the outcome of physical design constraints) is observed to be roughly matched by allometry in capacities for demand (i.e. for energy expenditure). However, physiological rates most often fall far below maximum capacities and are subject to multi-step regulation. Thus, mechanistic explanations for the scaling of BMR and MMR must consider the manner in which capacities are matched and how rates are regulated at multiple levels of biological organization.
代谢控制分析表明，代谢途径中的通量是系统特性的结果，即由多个步骤共同控制，以及各种途径和过程之间的动力学相互作用。这意味着通量率的异速生长缩放必须根据与通量率调节相关的特性来理解。相比之下，考虑分支或类分形系统缩放的模型支持者认为，供应率决定代谢率。因此，仅供应的异速生长缩放就为代谢的异速生长缩放提供了充分的解释。对比较生理学文献中的实证数据进行考察发现，基础代谢率（BMR）由内脏器官内的能量消耗率驱动，并且BMR的异速生长缩放可以根据内脏器官的质量和代谢率的缩放来理解。器官代谢率代表组织代谢率的总和，而在组织内，细胞代谢率是多个过程共同调节的结果。运动期间的最大代谢率（MMR，以最大耗氧率VO2max衡量）也呈异速生长缩放，也受多个过程的控制，但主要归因于运动肌肉的耗氧。因此，对MMR缩放的分析必须考虑肌肉质量和肌肉能量消耗的缩放。与对称生长原理一致，观察到供应能力的异速生长（物理设计限制的结果）与需求能力（即能量消耗）的异速生长大致匹配。然而，生理速率通常远低于最大能力，并且受到多步骤调节。因此，对BMR和MMR缩放的机制解释必须考虑能力匹配的方式以及在生物组织的多个层面上速率是如何调节的。
