Characterization and Partial Purification of an Inducible Protein Related to Hexose Proton Cotransport of Chlorella vulgaris

Abstract

Cells of C. vulgaris induced for hexose transport contain a membrane-bound protein component that is missing in non-induced cells. This was shown by double labeling experiments with [14C]phenylalanine and [3H]phenylalanine applying the method of Kolber and Stein. The specific protein is completely absent from soluble fractions. An enrichment of the double-labeled peak was observed in membrane fractions enriched in plasmalemma. The best purification was obtained when cell walls were purified; the residual membranes attached to the walls contained the transport protein with a 12-times-higher specific activity than the crude extract. The transport protein had the characteristics of an intrinsic membrane protein. Its MW was 30,000 on sodium dodecylsulfate gels. The protein did not show sugar binding activity. Induced cells lose their state of induction with a half-life of about 4 h; 7 h after induction the double-labeled transport protein is no longer detectable.