Identification and characterization of a thermolabile antigen (TLAb, glyceraldehyde-3-phosphate dehydrogenase) in Saccharomyces cerevisiae.

Five thermolabile antigens (TLAa, TLAb, TLAc, TLAd, and TLAe) have been purified from Saccharomyces cerevisiae. Recently, we reported that TLAa was identical with yeast enolase (EC 4.2.1.11). In this paper, TLAb was identified as yeast glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) on the following bases: (1) Mr, N-terminal amino acid sequence, and isomer number of TLAb were the same as those of GAPDH; (2) anti-TLAb serum was reactive to GAPDH in the Ouchterlony test and in sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting; and (3) TLAb possessed GAPDH enzyme activity which was inhibited by anti-TLAb serum. The effect of various growth conditions on the proportion of three TLAb isoproteins (TLAb-1, TLAb-2, and TLAb-3) was examined. The proportion of two TLAb isoproteins (TLAb-1 and TLAb-2) changed depending on the cell growth phase the carbon sources, and sodium chloride shock. It is concluded that environmental stress has a differential effect on the biosynthesis of TLAb isoproteins.