AN ALTERED T-2-BETA TRANSLOCASE OF THE GLUCOSE-6-PHOSPHATASE SYSTEM IN THE MEMBRANE OF THE ENDOPLASMIC-RETICULUM FROM LIVERS OF EHRLICH-ASCITES-TUMOR-BEARING MICE

The inhibitory interactions of orthophosphate (P-i) with the glucose-6 -phosphatase system of intact microsomes derived from the livers of no rmal and Ehrlich-ascites-tumour-bearing mice reveal the appearance of a novel form of the T-2 beta translocase component of the glucose-6-ph osphatase system in tumour-stressed mice. Kinetic studies, with and wi thout 20 mM P-i, show a strictly classical competitive inhibition, wit h a K-i,K-P1, of 4.2 mM, with disrupted microsomes from both control a nd tumour-bearing mouse liver. Inhibition was also observed with intac t microsomes from livers of control mice, and contributions by both co mpetitive and non-competitive components of inhibition were quantified by calculation of K-is,K-P1 and K-ii,K-Pi values respectively. Howeve r, little inhibition was noted with intact microsomes from the livers of tumour-bearing mice. It is concluded that this novel form of T2B is less able to transport P-i, from the cytosol to the endoplasmic retic ulum lumen, perhaps because of the tumour-related increased K-m for P- i transport in this direction.