Transport of D-allose by isolated fat-cells: an effect of adenosine triphosphate on insulin stimulated transport.

D-allose, a glucose analogue, is not metabolized by isolated fat-cells and its distribution space at equilibrium in the cells is the same as that of triated water. Uptake of allose is inhibited by glucose and 3-O-methylglucose, stimulated by insulin and virtually eliminated by cytochalasan B. Counter transport of allose out of fat-cells against a concentration gradient can be induced by exogenous glucose but not by pyruvate. It is concluded that allose is transported into fat-cells by the same carrier mediated transport system as glucose and that it is a suitable analogue with which to study the glucose transport system. Insulin stimulated allose transport, into or out of the cell, but not basal transport, is inhibited by a brief exposure of isolated fat-cells to exogenous ATP or ADP (but not AMP or AMP-PNP). The antilipolytic effect of insulin is not affected. The ATP inhibition is slowly reversible. It is suggested that ATP phosphorylates a membrane component and thereby blocks transmission of signal from the insulin receptor to the carrier system. Indirect evidence suggests that ATP does not alter the affinity of the insulin or glucose binding sites. Insulin decreases the Km of glucose metabolism of CO2 and lipid in isolated fat-cells and increases the Vmax. However,the hormone has no effect on the Ki of glucose as an inhibitor of allose transport. The glucose analogue, 3-O-methyl-glucose, also inhibits both glucose metabolism and allose transport. The Ki for both these processes is similar and is not affected by insulin. These results support the view that the effect of insulin on glucose transport is to raise the Vmax without a change in the Km. It appears further that sugar transport is not the major rate limiting step in metabolism at high glucose concentrations in the absence of insulin, or at most glucose concentrations in the presence of the hormone.