Test for missynthesis of lactate dehydrogenase in aging mice by use of a monospecific antibody

Comparison of specific activities of enzymes from young and old dogs and mice

Aldolases A and B (EC 4.1.2.13) and liver cytoplasmic superoxide dismutase (EC 1.15.1.1) have been purified from young and old dogs and mice. The specific activities of these enzymes were measured and show no diminution with age. In addition, dog aldolase B, dog liver superoxide, and mouse liver aldolase were titrated in crude extracts with specific antisera. No accumulation of cross-reacting material with age was detected. The electrophoretic mobilities of these enzymes and the susceptibilities of dog aldolases A and B to trypsin digestion were also unchanged. These results are additional evidence that the accumulation of inactive enzymes is not an invariable concomitant of aging.

Analysis of the translational capacity of the male accessory gland during aging in Acheta domesticus

The protein synthesizing capacity of the male cricket accessory gland was inspected for changes associated with aging by analysis of organs from young (2 weeks post-imaginal molt), middle-aged (4 and 6 weeks) and senescent (8 weeks) animals. Total RNA content and the percentage of ribosomes in polysomes show an increase up to 4 weeks and then a steady decline. The rates of protein synthesis by young and old glands incubated in vitro were comparable, although the old glands were significantly less efficient in precursor uptake and therefore showed lower incorporation levels. The overall picture appears to be one of a steady but unspectacular decline in protein synthesizing capacity in aging animals. The quality of the secretory proteins formed by young and old glands was inspected by SDS--polyacrylamide gel electrophoresis and by isoelectric focusing, using both wide and narrow pH-range gels. While some differences in the banding patterns of isoelectric focusing gels were detected, they were eliminated by the inclusion of Triton X-100 in the gels. No other evidence for age-associated qualitative or quantitative changes was detected, strongly suggesting that proteins from young and old glands are identical.

Aldolase B in the liver of senescent rats

The process of enzymatic aging was studied in livers of adult and senescent rats for aldolase B. No "cross-reacting material" was found in livers of 27 to 30-month-old rats, estimated by the ratio aldolase activity-antigen amount. The activity towards the two substrates of aldolase, fructose 1,6-diphosphate and fructose 1-phosphate did not vary in senescent animals. Moreover, other physico-chemical properties of the enzyme such as thermal inactivation, immunological reactivity and Michaelis constant remain unchanged. These results provide arguments against the occurrence of errors in protein synthesis as a cause of aging.

Evidence contrary to the protein error hypothesis for in vitro senescence

A strain of diploid fibroblasts, obtained from the skin of a male infant, was cultured in vitro and cells were tested throughout their lifespan for the appearance of altered glucose-6-phosphate dehydrogenase (G-6-PD) detected either by thermostability studies or by immunotitration. No significant difference was found in the proportion of thermolabile enzyme in 31 young cultures (4.8 +/- 1%, S.E.), in comparison with that in 19 old cultures (4.9 +/- 1%, S.E.). Old cultures had ceased active cell division (49-60 doublings); DNA replication, measured by [3H]thymidine uptake over a period of 24 hours, was limited to less than 5% of these cells. Young cells (5-22 doublings) had a [3H]thymidine labeling index of 75-85%. Titration of G-6-PD activity in extracts of young and old cells with neutralizing antibody directes specifically against G-6-PD failed to detect an increment of enzymatically defective G-6-PD in old cells. The thermostability studies were capable of detecting altered G-6-PD in skin fibroblasts from a female heterozygous for a thermolabile mutant of G-6-PD, and in fibroblasts treated with a proline analogue, azetidine carboxylic acid. The immunotitration technique was also capable of detecting catalytically altered G-6-PD from the thermolabile mutant and G-6-PD inactivated with N-ethylameimide. These findings argue against a protein error catastrophe as the cause of in vitro clonal senescence.