Identification and Characterization of a Thermolabile Antigen (TLAa,Enolase) in Saccharomyces cerevisiae

Five kinds of proteins of Saccharomyces cerevisiae were recently purified to a homogeneous state and identified as yeast cell surface antigens (TLAa, TLAb, TLAc, TLAd, and TLAe), but their physiological functions remained uncertain. In this paper, TLAa was identified as a yeast enolase (EC 4.2.1.11) from the following evidence: (1) molecular weights and amino acid compositions of both proteins were similar, (2) the N-terminal 22 amino acid sequences of both proteins were the same (3), TLAa had enolase activity, and (4) the authentic yeast enolase gave a positive reaction with anti-TLAa serum in the Ouchterlony immunodiffusion test and the immunoblotting test. Two isoproteins of TLAa (enolase) were separated by non-denatured polyacrylamide gel electrophoresis and detected by immunoblotting with anti-TLAa serum. The contents of the two isoproteins varied depending on the following culture conditions: glucose starvation, growth in the presence of non-fermentable carbon sources, and growth in media containing sodium chloride and 2-deoxyglucose. The contents did not vary, however, with heat shock treatment or with growth in media containing sodium azide, tunicamycin, or sorbitol. These results showed that TLAa was a cytoplasmic antigen, and that its synthesis was regulated by some environmental stresses.