Modified Kidney Sodium Potassium Adenosine-Triphosphatase Kinetics in Protein Energy Malnutrition

Abstract

Erythrocyte membrane and kidney microsomal Na, K-ATPases have been shown to be elevated in children suffering from kwashiorkor and in protein energy malnourished (PEM) rats. Kinetic properties of kidney microsomal Na, K-ATPase were studied in PEM rats to understand further the mechanism of this elevated activity. From the Arrhenius plots no significant differences were seen in the critical temperature and energy of activation of Na, K-ATPase between the control (C), energy-restricted (ER), and protein-restricted (PR) rats. Changes in the apparent K0.5 values of Na+, K+, and ATP were of much smaller magnitude, and increased Vmax was found to be mainly responsible for the observed increase in Na, K-ATPase activity in PEM rats. The Hill coefficient with ATP as substrate was found to be 1.62 in all three groups. Vmax/Km: a broad index of physiological efficiency, remained unaltered with K+ as a substrate in the ER rats, but was higher by 60% in PR rats as compared with the control value. In the Na+-activated component, the physiological efficiency in protein restriction was higher by 60% in relation to energy restriction. These results lead to the conclusion that the increased Na, K-ATPase activity in kidney microsomal preparations, from PR rats is attributable to modifications in the enzyme site and that energy restriction, in fact, results in a lowering of the physiological efficiency of Na, K-ATPase by affecting the Na+-site. Altered lipid microenvironment if any, does not appear to contribute to changes in Na, K-ATPase activity in PEM since neither Arrhenius plots nor Hill coefficients (ATP) showed any modification.