Hymenolepis diminuta: The non-saturable component of methionine uptake

Abstract

Lussier P. E., Podesta R. B. and Mettrick D. F. 1982. Hymenolepis diminuta: the non-saturable component of methionine uptake. International Journal for Parasitoiogy 12: 265–270. The concentration dependence of in vitro unidirectional methionine influx by Hymenolepis diminuta was analysed by the relation: J = (J m C b ) (K t + C b ) + K d(C b ) , where J m is the maximum uptake rate, K t is the the apparent affinity constant and C b is the medium substrate concentration. The linear component was separated using an asymptotic least squares curve fitting procedure and the resulting constant, K d , is thought to be an apparent permeability coefficient. K d may be a reflection of a simple diffusive component, a second mediated component or a combination of a passive and mediated influx. The low Q 10 value of the K d 's for methionine uptake ( Q 10 = 1.31) indicated that this component is probably a reflection of diffusion within the membrane. However, the decrease in the K d component in the presence of leucine and glycine, implies that there is also a small, second, mediated component in addition to the diffusive component. K d derived from the asymptotic portion of the concentration-flux relation was compared with the residual flux of methionine after near complete inhibition of the mediated component with leucine and glycine. The K d component was found to be pH-sensitive, increasing as the pH decreased and was not affected by external sodium. Results indicate that the mediated component of methionine influx was accelerated by increasing external Na + and H + concentrations.