This project contains a program aimed at gaining a better understanding of the regulation of nutrient transport in untransformed and transformed animal cells in culture. Outlined are culture conditions that will be used to cause large increases in transport activity in intact chick embryo and hamster cells. Methods for the preparation of membrane vesicles retaining carrier activity are described. Membrane vesicles are used to characterize carrier activity in a system free of metabolic factors and as a primary step in carrier purification. Selective labeling of carriers is based upon incorporations of radioactive tracers into membrane proteins during culture periods known to cause major increases and decreases of carrier activity. Methods for selective extraction of membrane proteins are also outlined as is the possible development of artificial assay systems, reconstitution of transport in liposome preparations. Electrophoresis and autoradiography are to be used through purification and reconstitution studies in attempts to identify the carriers. The possibilities that modification of plasma membranes and subsequent degradation contribute to control is discussed and methods designed to test the possibility are described. Efforts are to be made to compare untransformed ("normal") cells with their transformed counterparts.