Alternate energy transduction routes in chemically skinned rabbit psoas muscle fibres: a further study of the effect of MgATP over a wide concentration range

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Abstract
Complex stiffness data were studied over an extended range of MgATP concentrations (3 µm-5mm) in single fibres of Ca2+-activated, chemically skinned adult rabbit psoas. The data were analysed in terms of a model involving three exponential processes, the presence of which was previously observed in fully activated muscles. As fibres were transferred from a rigor solution into solutions of gradually increasing MgATP concentration, the three processes appeared sequentially, each with a uniqueK m. The order of appearance as MgATP increases is (1) the slowest of the three processes [designated process (A)], (2) the fastest of the three processes [designated (C)], and (3) process (B), which occupies the middle range of frequencies; theK ms are approximately 10 µm, 0.2mm, and 0.8mm, respectively. The single phase advance [process (A)] remaining at very low substrate concentrations was found to be better described by a distribution of rate constants than by a single rate constant. The influence of substrate concentration on these processes is examined and two parallel hydrolysis routes are suggested as a possible mechanism.