Heat-labile isozymes of isocitrate lyase from aging Turbatrix aceti

The temperature stabilities of pure isocitrate lyase, isolated from young and old $\text{Turbatrix aceti}$, have been compared. The “old” enzyme shows the presence of a heat-labile component lacking in the enzyme derived from young organisms. This component has been shown to be associated with two of the five isozymes comprising the isocitrate lyase. A mechanism is proposed which might account for the presence of altered enzymes in aged organisms.