Lynn S. Grinna

Age related changes in the lipids of the microsomal and the mitochondrial membranes of rat liver and kidney

The lipid contents of the microsomal and mitochondrial membrane fractions of liver and kidney were determined in 6 and 24 month old rats. A significant age related increase in the molar ratio of cholesterol/phospholipid was observed in all membrane fractions. A significant age related reduction of phospholipid was noted in the microsomal fractions of liver and kidney. The relative amount of phosphatidylethanolamine was found to decrease in all membrane fractions during aging. Membrane glyceride content, however, remained relatively constant with age. Significant increase in oleic acid was seen in the neutral lipid of both liver and kidney and in the polar lipid of kidney. Significant increase in docosahexaenoic acid and significant decrease in linoleic acid were seen in the polar lipid of the liver membrane fractions. Possible alterations in membrane physiochemical properties and in membrane function due to these age related lipid changes are discussed.

Age-related changes in membrane lipid content and enzyme activities

Abstract 1. 1. Microsomal and mitochondrial fractions were isolated from livers, kidneys and hearts of 6- and 24-month-old rats and the specific activities of several membrane-bound enzymes were determined. Differences were seen in the activities of the enzymes at the different ages. 2. 2. The phospholipid to protein ratios of the isolated fractions were determined. The phospholipid of the liver and kidney microsomal fractions was decreased in the old animals. No changes were seen in the ratio of membrane phospholipid to total lipid. 3. 3. Kinetic analysis was performed on two membrane-bound enzymes isolated from 6- and 24-month-old animals. Altered, perhaps inhibited, forms of the enzymes were indicated. 4. 4. It is concluded that enzyme changes observed to occur during aging are not directly correlated with in vivo phospholipid loss. The regulating influence of membrane conformation on the activity of bound enzymes, however, does appear to change.

Changes in cell membranes during aging.

Age-related changes in the morphology and composition of mammalian membranes are reviewed. Certain age-related changes in the functional character of mammalian membranes are highlighted. The need for integrated studies of membrane changes during aging is discussed.

Lipid peroxidation in livers and kidneys from young and old rats.

Abstract Lipid peroxidation was measured in young (6 months) and old (24 months) rat tissue homogenates and microsomal fractions. Decreases in lipid peroxidation were noted in homogenates and microsomes from old animals. The decreases in liver and kidney appear due to reduced ascorbic acid content and the appearance of an inhibitor in the soluble phase. In addition old kidney microsomal fractions contain a membrane associated lipid soluble inhibitor. The significance of these inhibitors and of lipid-protein interactions in the regulation of lipid peroxidation are also discussed.

Age-Related Alterations in Membrane Lipid and Protein Interactions: Arrhenius Studies of Microsomal Glucose-6-Phosphatase

Arrhenius plots of glucose-6-phosphatase (EC 3.1.3.9) activity in liver microsomes from 6-month-old rats (young) showed discontinuities at 39, 30, 20 and 12 degrees C and change in activation energy at 20 degrees C. The enzyme activity in kidney microsomes of young rats showed essentially the same thermal discontinuities. In liver microsomes of 24-month-old rats (old) the enzyme showed discontinuities at 38, 30, 24 and 16 degrees C but not at 12 degrees C and the activation energy changed at 24 degrees C. In kidney microsomes of old rats discontinuities were seen at 38, 31, 22, 16 and 12 degrees C and the activation energy was constant from 0 to 41 degrees C. These results indicate that the interactions of membrane components are altered with age.

Kinetic analysis of the age related differences in glucose-6-phosphatase activity

Abstract Kinetic analysis was performed on glucose-6-phosphatase of 6 and 24 month old rat liver and kidney microsomal fractions. In untreated microsomal fractions of old liver the enzyme displayed decrease in V. In untreated microsomal fractions of old kidney and enzyme displayed decrease in V and increase in Km. Triton X-100 and NH4OH were used to disrupt the membranes and to activate the enzyme. The treatments lowered the Km of the enzyme. The activated enzymes of the young and old liver had similar Km but the old liver still displayed a lower V. The same results were found for the kidney. Kidney membranes were found to contain about 50% latent enzyme activity which was released by the treatments. The liver did not contain latent enzyme activity. The age related reduction in glucose-6-phosphatase activity appears to be due to reduction in the amount of enzyme present in the membranes. The membranes from old animals appear to be more labile to manipulation than the membranes from young animals.

Turnover of lipid components in liver microsomes, mitochondria and plasma membrane of 6-, 12- and 24-month old rats

The turnover of lipid was examined in the livers of 6-, 12- and 24-month old rats. Heterogeneity of turnover was noted for each membrane fraction. The lipid turnover rate was highest in 12-month old rats and was the same in 6- and 24-month old rats. The higher rate of lipid turnover at 12 months was observed in both the neutral and polar lipid components of the liver membranes. In the polar lipid fractions isolated from the microsomal and mitochondrial membranes the increase in lipid turnover rate at 12 months was related to increase in the turnover of phosphatidylethanolamine.

Multiple thermal discontinuities in glucose-6-phosphatase activity

The temperature dependence of glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase EC 3.1.3.9) was studied in rat liver and kidney microsomal fractions. Arrhenius plots were non-linear and showed four distinct discontinuities in enzyme activity over the temperature range 2-41 degrees C. The discontinuities occurred at approx. 39, 30, 20 and 12 degrees C in the liver and were similar to this in the kidney. Changes in the energy of activation for the enzyme were noted at approx. 20 degrees C in both tissues. The multiple discontinuities in glucose-6-phosphatase activity are viewed as a reflection of complex reorganization and/or change in physical state of the membrane components, primarily lipid.