Studies on the physical state of water in living cells and model systems. XI. The equilibrium distribution coefficients of pentoses in muscle cell water: their dependence primarily on the molecular weights of the pentoses and lesser dependence on their stereospecificity

Studies of the metabolism of four pentoses (D-, and L-arabinose; D-, and L-xylose) in frog muscle at 0 degree C revealed that all are metabolized at extremely slow rates. As a result, the metabolic degradation of these pentoses does not significantly affect their equilibrium distribution in muscle cells at this temperature at least. Of the four stereoisomers, three (L-xylose, D-arabinose, L-arabinose) were found exclusively or almost exclusively in the cell water, demonstrating a rectilinear distribution pattern; the equilibrium distribution coefficients (q-values) obtained from the slopes of these rectilinear distribution curves are 0.256, 0.274, and 0.271 respectively. The fourth pentose, D-xylose, is apparently partially adsorbed. With the aid of the equation for solute distribution according to the association-induction (AI) hypothesis, the data for this sugar can also be fitted with a theoretical curve calculated on the basis of a q-value close to those for the other three pentoses. The close similarity of the q-values of pentoses which are sterically different, but have identical molecular weights, provides further confirmation of the "size rule", a prediction of the polarized multilayer (PM) theory of cell water, according to which, the q-values are as a rule primarily determined by the molecular weights of the solute and to a lesser extent dependent on its stereospecificity.