The biosynthesis of C14- labeled lipids by isolated spermatozoa of man and fish
Minassian, Elaine Shakay
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The incorporation of C14 label into the lipids of the spermatozoa of man and fish (the alewife, Alosa pseudoharengus,) was studied. Washed spermatozoa of man and the alewife were incubated in vitro under aerobic conditions with glucose-C14 (r.1.). The sperm cells were extracted with chloroform-methanol, and the crude lipid extracts were purified to remove radioactive contaminants. The lipid extracts were fractionated into the major classes of lipids by column chromatography and further separated by thin-layer chromatography. Glycerides, phosphatides and cholesterol were isolated and identified and their radioactivity was determined. C14 label was found exclusively in the lycerol portion of the glycerolipids of the spermatozoa of both man and the alewife. The rates of incorporation of glucose-C14 into the total lipids were 54.4 ummoles/1010 human spermatozoa/hour and 1.8 ummoles/10^10 alewife spermatozoa/hour. In the sperm lipids of both species the glycerides were the most actively labeled components with the diglycerides having the highest specific activities and the triglycerides being the most abundant components. Whereas in human spermatozoa the glyceride content was 20% of the total lipids, in the alewife spermatozoa the fraction constituted only 4% Cholesterol, 14 - 15% of the total sperm lipids in both species, was not labeled. The polyglycerophosphatide fraction was the most abundant and the most actively C14-labeled component in the phosphatides of alewife spermatozoa. Most of the radioactivity incorporated in the phosphatides of human spermatozoa was found in the lecithin and cephalin fractions. Lecithin was the phosphatide of highest specific activity. By means of infrared spectroscopy, evidence of the presence of plasmalogen was found in the phosphatides of human, but not of alewife spermatozoa. Unlike mammalian spermatozoa, fish spermatozoa have poor glycolytic capacity. Nevertheless, the present work shows that fish spermatozoa can utilize glucose for the synthesis of glyceride glycerol at adequate rates. The demonstration of the biosynthesis of lipids from glucose by the spermatozoa of man and fish suggests that sperm may utilize carbohydrate not only for the maintenance of motility through the energy generated by glycolysis, but also for the replenishment of lipid reserves.
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