INTRACELLULAR ORGANIZATION - EVOLUTIONARY ORIGINS AND POSSIBLE CONSEQUENCES TO METABOLIC-RATE CONTROL IN VERTEBRATES

We adopt the position that metabolism originated at (or near) mineral surfaces prior to the origin of the first cells. Based on current views of the organization of contemporary animal cells we speculate that the metabolism of the immediate ancestors of eukaryotic cells required these non-biological surfaces, but that the latter were subsequently replaced by membranes, and nuclear and cytoplasmic matrix proteins which, we argue, remain as required participants in the intermediary metabolism of contemporary eukaryotic cells. The idea that such an intracellular organization could have provided a fundamental means by which to control metabolic rate at the level of the intact animal is considered next. In the case of vertebrates we suggest that the organismic level of control might operate through the rate of capillary blood flow, as proposed in the Flow Theory of Coulson (1986): by controlling the rate at which the organized enzyme arrays within the cells arc perfused with substrate, cellular metabolic rates could be set throughout the organism in an integrated fashion. Although there are problems with this linkage the interesting possibility arises that the metabolic rate of individual cells may be subservient to the organism, being driven not so much by the well known intracellular controls of concentration-based-biochemistry as by the flow of nutrients through the cells.