Temperature dependence of amino acid transport in ehrlich ascites cells: with results which bear on the A-L distinction

Abstract

We have examined the temperature dependence of maximal flux, JM, the half-saturation value, Km, and of the linear components, k, of the initial transport flux for -methionine, -tryptopah, glycine, -alanine, [alpha]-aminoisobutyric acid and -phenylalanine in Ehrlich ascites cells. For -alanine, [alpha]-aminoisobutyric acid and -phenylalanine we examined the initial flux in transport and in exchange for cells in Na+-containing and in Na+-free media.The maximal flux in transport falls with decrease in temperature, the activation energies falling in the range 11-20 kcal/mole.The Km decreased with decrease in temperature for -phenylalanine and -tryptophan with apparent activation energies of 20 and 15 kcal/mole respectively, For -methionine, glycine and -alanine the Km showed no dependence on temperature whereas for [alpha]-aminoisobutyric acid in increased as the temperature fell. For all amino acids, the Km appeared to be more variable a parameter of the initial flux than was the maximal flux.The results for the linear component of the uptake, k, also were highly variable, but k did decrease with a fall in temperature with activation energies falling in the range 5.8-17.7 kcal/mole.