Triosephosphate isomerase from young and old Turbatrix aceti.

Triosephosphate isomerase (EC 5.3.1.1) has been purified from young and old Tubatrix aceti. The enzyme shows a sharply lower specific activity in homogenates from old nematodes compared to similar preparations from young animals. However, when the enzyme activity of the respective homogenates was adjusted to the same level, equal amounts of antiserum (prepared to pure “young” triosephosphate isomerase) were required to remove the activity. Therefore, the lower specific activity observed in “old” homogenates was due to the presence of less enzyme and not to “altered” enzyme. The same results were obtained by immunotitrations of pure preparations of “young” and “old” enzyme. Moreover, in contrast to results reported for other enzymes, the specific activity of “old” triosephosphate isomerase, during purification, rose to the same value as that of pure “young” enzyme. The evidence indicates that altered triosephosphate isomerase does not exist in old T. aceti. The above results contradict the idea of an “error theory” in which all proteins would develop altered sequences. Pure triosephosphate isomerase (old or young) from T. aceti consists of two subunits, each of molecular weight 26,500. No isozymes could be detected.