Partial Purification and Characterization of Inducible Transport Proteins of Chlorella

Abstract

Autotrophically grown Chlorella vulgaris cells show a low rate of hexose and amino acid uptake. After pretreatment with glucose or glucose analogues the rate of uptake of hexoses and of six amino acids (catalyzed by one hexose- and two amino acid transport systems) is increased one hundred-fold or more. Induced cells possess at least two additional membrane proteins, which are detectable after radiolabelling. Their apparent molecular weight on SDS gels increases with increasing acrylamide concentration and possibly correct values were estimated by extrapolation to be about 65,000. The putative hexose transport protein does not seem to be N-glycosylated.

The proteins were enriched approximately 30fold starting from a partly purified membrane fraction and following a purification procedure worked out for E. coli lac-permease (Newman et al., 1981, J. Biol. Chem. 256, 11, 804). The purified extract from induced cells contained a protein which was detected as diffuse band after silver staining; this protein was absent from the extract of non-induced cells. The stained band corresponded to the radiolabelled proteins described above.