The effect of age on the protein degradation system in the nematode Turbatrix aceti.
The administration of 0.2% of the amino acid analogues canavanine and 6-fluorotryptophan to young nematode cultures caused the appearance of inactive but antigenically reactive aldolase molecules at levels comparable to those found in old untreated cultures. Concomitant with the rapid appearance of inactive enzyme molecules a rapid rate of mortality could be detected. Mortality, however, ceased when a massive disappearance of inactive molecules could be observed. Subsequently, mortality resumed at a rate similar to that found in untreated cultures. The NaH14CO3 method of Swick and Ip (J. Biol. Chem., 249 (1974) 6836-6841) was used to estimate the half-life of proteins. The half-life of total soluble proteins in old and intermediate age animals was 4 times and 2.5 times longer, respectively, than that of young nematodes. No differences could be discerned in the half-lives of total proteins between analogue-treated and control animals of young and intermediate ages. However, the rate of disposal of inactive molecules was slower in intermediate age as compared to young animals as it was closely related to the general rate of protein degradation in the different age groups. The results suggest that (a) the proportion of inactive enzyme molecules encountered in old animals is potentially detrimental, (b) the decline in efficiency of the degradation system in older animals may account for the accumulation of altered protein molecules in aging organisms.