Abstract
When deprived of D-glucose for 24 hr, chicken embryo fibroblasts exhibit a marked increase in hexose transport activity compared with that of control cells. Scatchard analysis of [3H]cytochalasin B binding to starved cell plasma membranes (46 pmol/mg) indicated a six-fold increase compared with fed cell plasma membranes (7.5 pmol/mg). Irradiation of starved cell plasma membranes with high-intensity UV light in the presence of 0.5 microM [3H]cytochalasin B resulted in covalent labeling of polypeptides of Mr 52,000 and 46,000. In fed cell plasma membranes irradiated under the same conditions, both polypeptides were labeled but at greatly decreased levels. In fact, labeling of the Mr 52,000 polypeptide was barely detectable. The amount of D-glucose-sensitive [3H]cytochalasin B covalent insertion into these membrane components was increased 11 +/- 2 (n = 4)-fold in starved versus fed cell plasma membranes. Photoaffinity labeling of both polypeptides in starved cell plasma membranes was inhibited by D-glucose, 3-O-methylglucose, 2-deoxyglucose, cytochalasin B, and cytochalasin A but not by D-sorbitol, L-glucose, or cytochalasin E. Half-maximal inhibition of labeling of the Mr 52,000 polypeptide occurred at 8 mM D-glucose whereas, for the Mr 46,000 polypeptide, half-maximal inhibition occurred at 40 mM D-glucose. It is concluded that (i) two hexose transport proteins, one of Mr 46,000 and one of Mr 52,000, have been identified in chicken embryo fibroblasts and (ii) the increased affinity labeling of these transporter components after cell starvation may reflect increased numbers of transporters in the plasma membrane.