N. K. Sarkar

THE EFFECT OF AGE ON THE VARIATIONS OF DEOXYRIBONUCLEIC ACID, RIBONUCLEIC ACID AND TOTAL NUCLEOTIDES IN LIVER, BRAIN AND MUSCLE OF RAT.

Abstract The effect of age beginning from infancy to advanced age on the variations in the concentrations of deoxyribonucleic acid, ribonucleic acid and total nucleotides in liver, brain and muscle of rats was studied. The concentrations of DNA, RNA, and nucleotides in rat embryonic tissues were also determined. In the brain and muscles of very young rats the DNA and RNA concentrations are remarkably high and drop sharply and extensively, right from there with increasing age. In the liver the DNA and RNA concentrations show an increase after birth and drop rapidly thereafter, and then follow the same pattern of changes as noted in the case of muscle or brain. In muscle and brain tissues of rat embryo the concentrations of DNA and RNA are much higher than are found in corresponding tissues of young rats while in liver tissue of rat embryo their concentrations are much less. In young adults (100–400 g) the DNA and RNA do not undergo very significant change and in old age the RNA concentration goes up and the DNA concentration goes down, slightly in both cases. If the DNA and RNA values are expressed per organ, their values (contents) in liver show a steady increase with age. The total nucleotide concentration in brain is considerably higher than that found in muscle and liver. In muscle its concentration is higher than that found in liver.

Nucleic acid and protein metabolism in Tribolium confusum Duval: I. The variation of nucleic acid and nucleotide concentration in Tribolium confusum in relation to different stages of its life cycle

Summary The variation of deoxyribonucleic acid, ribonucleic acid and free nucleotide concentrations in Tribolium confusum , Duval in relation to different morphological changes has been studied. Considerable variation in the concentration of the two nucleic acids have been found in the embryonic stage as well as during larval phase. The concentrations of the two nucleic acids show, in the beginning, a sharp steady increase, then reach the maximum heights and finally drop rapidly. They remain constant thereafter until the insects are transformed into pupae. When the variation of DNA, RNA and growth with age are all considered together it becomes evident that in insects RNA synthesis precedes protein synthesis (growth) and follows DNA synthesis. The results also indicate that protein synthesis can be considered as an index of growth. It has been noted that the concentrations of free nucleotides measured by optical density determination method and by chemical method (see the experimental section) agree very well when applied to TCA-extracts obtained from insects, upto 14 days old (i.e. as long as the insect can be considered as larva), but when applied to TCA-extracts obtained from pupae or adult insects the results differ widely. The optical density of such TCA-extracts show a steady and sharp increase with age, between 16 to 30 days. This sharp increase in optical density as we have noted suggests that during this period a new compound is synthesised in these insects which interferes with the absorption of the nucleotides at 260 m μ . Addition of uric acid to RNA does not change the absorption of RNA at 260 m μ whereas addition of catechol, a dihydroxyphenolic compound does so. This might be considered to indicate that a compound which can interfere with the absorption of nucleotide at 260 m μ is being continuously synthesised in the insect during the latter stages of its life cycle. In all probability this compound appears to be a polyphenolic compound, the isolation and characterization of which are now being investigated and will be reported separately.

Biochemical changes in progressive muscular dystrophy: I. Nucleic acid metabolism in normal and dystrophic rabbit and mouse liver, brain and muscle☆

Abstract In muscles, livers and brains of rabbits as well as in mice, exhibiting progressive nutritional and hereditary muscular dystrophy, a regular increase in DNA and RNA concentrations are noted. Contrary to this, free nucleotide concentration steadily decreases. In acute stage of the disease a three fold increase in DNA and a two fold increase in RNA over the control values in skeletal muscle of rabbits are observed. In mice these changes are a little less marked. In guinea-pigs, exhibiting the same degree of nutritional dystrophy, DNA is only increased while RNA does not show any significant change. Protein concentration too gradually declines and in acute stage of dystrophy it is decreased by 26–28 per cent of the control value. These changes of nucleic acid, free nucleotide and protein concentrations in all tissues can be reversed to normal levels by supplying adequate amount of vitamin E with the diet to the rabbits and guinea-pigs which had 60–70 per cent of the disease. From the results presented in the paper, it may be concluded that of the two nucleic acids, at least, one of them (DNA) shows a steady increase in the concentration in skeletal muscle as well as in other organs like liver and brain of rabbits and mice exhibiting either nutritional or hereditary muscular dystrophy. DNA changes can be considered as an index of the degree of the disease progressed.

THE EFFECT OF AGE ON THE VARIATIONS OF NUCLEASE ACTIVITIES AND THEIR POSSIBLE FUNCTIONS IN RAT LIVER.

Abstract The measurement of the activities of different nucleases in homogenates and mitochondria of rat liver reveals that their activities are greatly increased if the determinations are carried out either in the presence of Triton X-100 or after freezing and thawing. The relative increases in the activities of these enzymes in mitochondria are considerably higher than those in homogenates if the activities are measured in the presence of Triton X-100. When the effect of age on the activities of these enzymes in the livers of rats is studied, it is found that their activities are much higher in the livers of very young and old rats. In young adult rat livers the activities of these enzymes are much less and during the period beginning from 10 weeks to 10 months, no significant changes in their activities could be observed. On the basis of the results obtained in the course of this investigation, it has been suggested that these enzymes might be in some unknown way involved in the synthesis of DNA and RNA in very young rats, while in old age they act exclusively as degradive enzymes.

Effect of age on the incorporation of C14 thymidine into DNA, catalysed by soluble extract of rat liver☆

Abstract The ability of rat liver (high speed supernatant fraction) to synthesise DNA when two stranded DNA acts as a primer, decreases steadily with age whereas it increases progressively if heat-denatured DNA is used as a primer. The ability of the hepatectomized rat liver to synthesise DNA also increases after hepatectomy with time when two-stranded DNA acts as a primer but on and after 4th day of hepatectomy, this activity begins to drop and continues to decline thereafter until it reaches the level of activity observed before hepatectomy. On the other hand, if heat-denatured DNA is used as a primer the activity at first decreases, then increases steadily until it reaches the level of activity observed before hepatectomy. The reaction depends on Mg++ and cannot be replaced by any other metal, its action can however be stimulated by adding Ca++ but not by any other metal.

Effects of metallic ions and reducing agents on the incorporation of amino acids into soluble ribonucleic acid and microsomal protein

Abstract The [14C]leucine incorporation into soluble RNA catalysed by leucine-activating enzyme, present in the high-speed supernatant fraction prepared from rat-liver homogenate, increased by two- to three-fold in the presence of Co2+ compared with that found in the presence of Mg2+ alone. Cobalt cannot be replaced by any other metal. This cobalt-activated amino acid-incorporating system is very strongly inhibited by Ni2+ and other reducing agents like cysteine, glutathione, and, to a lesser extent, by ascorbic acid. Incorporation of 14C is also inhibited by EDTA but is not blocked by cystine and methionine. The incorporation of 14C into s-RNA can also be catalysed by the high-speed supernatant fractions prepared from rat Walker tumour and Sarcoma 180. Another three-fold increase in the incorporation of 14C could be obtained when the various high-speed supernatant fractions are dialysed before use. This cobalt-activated, incorporating system is independent of ATP, but gives rise to hydroxamic acid formation when the high-speed supernatant fraction of rat liver is incubated with [12C]leucine, Co2+ and hydroxylamine in the absence of ATP. This system requires the presence of high-speed supernatant fraction and cannot be replaced by RNA and albumin. The incorporation in vivo of [14C]leucine into proteins can also be enhanced by 25–35% if the [14C]amino acid is administered to rats, along with Co2+ and this effect of Co2+ could not be duplicated by any other metal.