Enzyme adaptation as a biochemical probe of development and aging

Effect of dietary restriction on hepatic and renal phosphoenolpyruvate carboxykinase induction in young and old Fischer 344 rats

Food restriction is known to ameliorate many of the adverse physiologic effects of age. In this study, we have examined the effect of food restriction on the induction of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK) in liver and kidney following a 12-h fasting period in young (6 month) and old (24 month) ad libitum-fed and food-restricted male Fischer 344 rats. In the liver, following the 12-h fast, the activity of PEPCK increased approximately 2-fold in the young ad libitum fed rats and 3-fold in the young restricted animals. However, PEPCK activity remained unchanged in response to the 12-h fast in the 24 month old ad libitum fed rats. In the old restricted rats, the induction of PEPCK mimicked that of the young rats (PEPCK activity increased 2-fold within the 12-h fasting period). Therefore, dietary restriction not only enhanced the induction response in the liver in young rats, but also restored the induction of hepatic PEPCK in the old animals. In the kidney, there was no effect of age or dietary restriction on the induction of PEPCK as the activity of renal PEPCK did not change in response to the 12-h fast in any of the four groups of rats.

Effects of dietary protein level on hepatic microsomal mixed-function oxidase systems during aging in two generations of Syrian hamsters

Syrian hamsters were fed one of three levels of lactalbumin (10, 20, or 40%) from 4 weeks of age. Parents (F0 generation) and their offspring (F1 generation) remained for life on the parental diet. Randomly selected hamsters from both generations were killed at 0, 6, 18, 30, and 60 weeks to evaluate hepatic microsomal drug metabolism systems. Microsomal protein content rose with increased dietary protein in both generations of females at 30 and 60 weeks and in both generations of males at 18 weeks. Microsomal protein rose during life, but the timing and magnitude of the increase varied with sex, diet, and generation. Cytochrome P-450 content increased with elevation in dietary protein at most measurement times in females and at all measurement times in F1 generation males. Hepatic aryl hydrocarbon hydroxylase (AHH) and aniline hydroxylase (ANH) activities were influenced by dietary protein, primarily at 6, 18, and 30 weeks, and these values tended to decline between maturity and senescence. AHH generally increased as dietary protein rose, except at 30 weeks, at which time the group fed the medium protein level usually had the highest activity. ANH activity was either elevated in groups fed the 20 or 40% lactalbumin levels or depressed in these groups at 6 and 18 weeks when these values were influenced by dietary protein. The effects depended upon sex and generation. Age effects on hepatic microsomal metabolism in hamsters varied by sex and dietary protein and were somewhat different than those reported for other rodents.

Age-dependent gene induction in quail oviduct X. Alterations on the post-transcriptional level (enzymic aspect)

In quail oviducts the rate of synthesis of avidin, the biological end-point marker for the molecular events caused by progesterone, decreases with age. The cause of the reduced capacity of avidin induction has been studied on the molecular biological level polyadenylation of RNA which is one step in the process of post-transcriptional modification of heterogeneous nuclear RNA resulting in the formation of functional mRNA molecules. This novel approach was biochemically possible after the discovery of the poly(A) anabolic enzyme (poly(A) polymerase) and the two poly(A) catabolic enzymes (endoribonuclease IV and 5'-exoribonuclease). These enzymes are involved in the synthesis and degradation of the poly(A) segment of mRNA in vitro and most likely also in poly(A) metabolism in intact cell systems. Enzymatically controlled poly(A) metabolism of mRNA is regulated by the following interrelations: poly(A)-associated proteins and endoribonuclease IV; labilizing factor and poly(A)-associated proteins; 5'-exoribonuclease in cooperation with endoribonuclease IV and poly(A) polymerase. A close correlation between high levels of poly(A) catabolic enzymes and low rate of protein synthesis which was established in cell culture systems, seems also to be partially the biochemical cause for the reduced avidin synthesis in aging quail oviduct.

Age-related changes in inducible mouse liver enzymes: ornithine decarboxylase and tyrosine aminotransferase

The time required to induce two inducible hepatic enzymes, ornithine decarboxylase (ODC) and tyrosine aminotransferase (TAT), by growth hormone and dexamethasone, respectively, increases with age. Specific activity at the peak of induction is the same for all ages. On the other hand, for basal TAT the specific activity per unit of TAT antigen was found to decrease considerably with age. The half-life of ODC was determined after cycloheximide administration. The apparent half-life at the peak of ODC induction increases from 15 minutes in 3-4-month-old mice to 30 minutes in 24-month-old animals. Loss of efficiency in the protein degradation system is implicated in this phenomenon as no apparent differences could be observed in the susceptibility of ODC and TAT from young or old mice to chymotrypsin. ODC and TAT are activated by temperatures of up to 37 degrees C and 50 degrees C, respectively. ODC is inactivated at 50 degrees C while TAT is inactivated at 76 degrees C. "Young" ODC and TAT are more readily activated or inactivated by heating than the "old" enzymes.

Age-related changes in the hepatic endoplasmic reticulum: a quantitative analysis

Morphometric analysis demonstrated a twofold increase in the surface area of the hepatic endoplasmic reticulum in Fischer 344 rats between 1 and 20 months of age, followed by a significant decrease in this parameter between 20 and 30 months. These changes are attributed to the smooth-surfaced endoplasmic reticulum, since neither the rough-surfaced variety nor the Golgi membranes underwent any significant change in surface area as a function of the age of the animal.

Age-related changes associated with the induction of o-pyrocatechuic acid carboxylase in Aspergillus ornatus

Mycelial mats of Aspergillus ornatus grown on cellulose xanthate membranes placed on a defined agar medium showed o-pyrocatechuic acid carboxyalse activity which could be induced to over six times its basal level by the addition of 0.1% L-tryptophan to the medium. Exposure of mature mycelial mats to cyclohexamide prior to induction indicated that de novo protein synthesis was required for this induction to occur. The effect of age of this enzyme adaptation process was investigated by transferring membranes and mats of variuos ages from defined medium to fresh defined medium plus 0.1% L-tryptophan With increasing mycelial age, the basal enzyme activity level remained relatively unchanged while the level to which the enzyme could be induced decreased significantly. This decrease was linear when plotted against the mean cell age of mycelium, conforming to a general model of age-dependent modifications of the enzyme adaptation process proposed by Adelman. Several possible explanations of this phenomenon are discussed.