Hepatic lipid metabolism. Age-related changes in triglyceride metabolism.

Age-related changes in hepatic triglyceride formation have been described in developing rats. Triglyceride formation was measured in vitro in the presence of [14C]glycerol-3-phosphate, palmitate, ATP, CoA, and Mg2+ by using liver homogenates and microsomal fractions derived from various age groups of animals. Triglyceride formation was most active in one-day-old rats and then decrease with age. The increase in triglyceride formation following birth was prevented by the administration of puromycin or by denying suckling. In addition, changes in plasma and hepatic triglyceride concentrations, were also determined as functions of age. These studies suggest that the age of the animal significantly influences triglyceride metabolism.     

Sulfolipid metabolism in chlorella

When S-deficient cells of Chlorella cllipsoidea were incubated in radio-sulfate in light or in aerobic darkness for 1 hour, equal amounts of radioactivity were found in sulfolipid and glutathione but none was detected in sulfoquinovosyl glycerol which is one of the major S-compounds in this alga. No assimilation of radiosulfate was observed under anaerobic darkness.

To elucidate the function of sulfolipid in algal cells uniformly ³⁵S-labeled Chlorella cells were transferred to S-deficient culture medium or unlabeled normal culture medium and the changes of radioactivity in sulfolipid and the related compounds were followed. A) On incubating ³⁵S-labeled algal cells in S-deficient medium under photosynthetic conditions, the amounts of radioactivity in sulfate, sulfoquinovosyl glycerol and sulfolipid decreased rapidly. B) When ³⁵S-labeled cells were cultured photoautotrophically in unlabeled medium, no decrease of radioactivity was observed in sulfoquinovosyl glycerol and sulfolipid. C) A decrease of ³⁵S-sulfolipid and an increase of ³⁵S-sulfoquinovosyl glycerol were observed when the uniformly ³⁵S-labeled algal cells were illuminated in CO₂-free air.

When S-deficient Chlorella cells were incubated in ³⁵S-sulfolipid under photosynthetic conditions, significant radioactivity was found in the insoluble fraction of the cells. A similar result was observed when normal Chlorella cells were incubated in ¹⁴C-sulfolipid and CO₂-free air.

It is inferred from these observations that sulfolipid is a reservoir of sulfur and carbon compounds.

In order to ascertain if the sulfolipid is involved in the mechanism of photosynthetic oxygen evolution, the rate of photosynthesis was measured during the incubation of ³⁵S-labeled cells in a S-deficient medium. Parallelism was not observed between the rate of photosynthetic activity and the decrease of sulfolipid.

     

Acetone metabolism in sheep

1. Entry rates of acetone were estimated in normal and ketonaemic sheep by using a constant-infusion technique with [(14)C]acetone. Entry rates were less than 1mg./min. in normal and 2-6mg./min. in ketonaemic sheep. 2. Only 1-2% of plasma glucose is derived from acetone. 3. Labelling in lactate is consistent with the conversion of acetone into glucose through lactate. 4. There is significant labelling of blood but not rumen volatile fatty acids.     

Carbohydrate metabolism in Bifidobacteria

Members of the genus Bifidobacterium can be found as components of the gastrointestinal microbiota, and are believed to play an important role in maintaining and promoting human health by eliciting a number of beneficial properties. Bifidobacteria can utilize a diverse range of dietary carbohydrates that escape degradation in the upper parts of the intestine, many of which are plant-derived oligo- and polysaccharides. The gene content of a bifidobacterial genome reflects this apparent metabolic adaptation to a complex carbohydrate-rich gastrointestinal tract environment as it encodes a large number of predicted carbohydrate-modifying enzymes. Different bifidobacterial strains may possess different carbohydrate utilizing abilities, as established by a number of studies reviewed here. Carbohydrate-degrading activities described for bifidobacteria and their relevance to the deliberate enhancement of number and/or activity of bifidobacteria in the gut are also discussed in this review.     

Starch metabolism in leaves

Starch is the most abundant storage carbohydrate produced in plants. The initiation of transitory starch synthesis and degradation in plastids depends mainly on diurnal cycle, post-translational regulation of enzyme activity and starch phosphorylation. For the proper structure of starch granule the activities of all starch synthase isoenzymes, branching enzymes and debranching enzymes are needed. The intensity of starch biosynthesis depends mainly on the activity of AGPase (adenosine 5'-diphosphate glucose pyrophosphorylase). The key enzymes in starch degradation are beta-amylase, isoamylase 3 and disproportionating enzyme. However, it should be underlined that there are some crucial differences in starch metabolism between heterotrophic and autotrophic tissues, e.g. is the ability to build multiprotein complexes responsible for biosynthesis and degradation of starch granules in chloroplasts. The observed huge progress in understanding of starch metabolism was possible mainly due to analyses of the complete Arabidopsis and rice genomes and of numerous mutants with altered starch metabolism in leaves. The aim of this paper is to review current knowledge on transient starch metabolism in higher plants.     

微生物硒代谢机制研究进展

硒(Se)是人与动物生命必需的微量元素,在医学保健和工业制造方面有着广泛的应用。硒在环境中有四种价态,包括硒酸盐Se O42-(+6)、亚硒酸盐Se O32-(+4)、单质硒Se0(0)和硒化物Se2-(-2)。微生物在硒的形态转化中扮演了重要的角色,影响着环境中硒的生物地球化学循环。本文主要从自然界中硒的循环以及微生物与硒代谢机制两个方面阐述微生物对硒的生物地球化学循环的重要性。     

Folate metabolism in ageing

Important histochemical observations on the nervous system, obtained in the last years, showed characteristic changes in folic acid and in its main enzyme--dihydrofolate reductase--in the old nerve cells. In neurons, the enzymic activity gradually decreased and folic acid accumulated in ageing. Glial cells preserved or slightly increased the same folate enzyme, but folic acid markedly increased in senescence. Opinions and suggestions bound to these observations are presented.     

Ceramide metabolism in brain

Summary Ceramide is the fundamental structure and key intermediate of all sphingolipids. Biosynthesis and catabolism of brain ceramide, especially their relationship to the metabolism of more complex sphingolipids in brain, are reviewed. Human genetic diseases which involve altered ceramide metabolism are also discussed.