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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Variations in apparent mass of mammalian fast-type myosin light chains correlate with species body size, from shrew to elephant

Department of Oral Biology, The Ohio State University, Columbus, Ohio

Submitted 6 February 2006 ; accepted in final form 4 August 2006

A recent study (Bicer S and Reiser PJ. J Muscle Res Cell Motil 25: 623–633, 2004) suggested considerable variation in the apparent molecular mass (M_a), deduced from electrophoretic mobility, in fast-type myosin light chains (MLCF), especially MLC1F, among mammalian species. Furthermore, there was an indication that MLC1F M_a generally correlates with species body mass, over an 4,000-fold range in body mass. The results also suggested that M_a of other low-molecular-weight myofibrillar proteins is less variable and not as strongly correlated with body mass among the same species. The objective of this study was to test the hypotheses that the M_a of MLCs does, in fact, vary and correlate with species body mass. The electrophoretic mobilities of MLCF isoforms from 19 species, varying in size 500,000-fold, were quantitated. The results confirm that the M_a of MLC1F and MLC2F vary significantly among mammals, spanning a very broad range in body mass; the MLC1F M_a varies more than that of other low-molecular-weight myofibrillar proteins; and there is a significant correlation between species body mass and MLC1F M_a. Differences in MLC1F M_a among five species can be accounted for by differences in the reported amino acid sequence, especially the length of a common polyalanine region near the NH₂-terminal actin-binding site. The possibility that the differences in MLC1F sequence among mammalian species, in and adjacent to the actin-binding region, are related to differences in modulation of cross-bridge kinetics in species with diverse locomotion kinetics is discussed.

isoforms; contractile proteins; myofibrillar proteins; body mass; scaling

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