Nucleic acid metabolism of mammalian spermatozoa

K A ABRAHAM & P M BHARGAVA

Regional Research Laboratory, Hyderabad-9, India

Published in: Biochemical Journal, 1963, 86, 298-307.

Abstract:

The absence of ribonucleic acid from spermatozoa has been reported by several workers (Brachet, 1933; Mauritzen, Roy & Stedman, 1952; White, Leslie & Davidson, 1953; Mann; 1954; Daoust & Clermont, 1955; Bhargava, Bishop & Work, 1959a). RNA is considered to be an essential component of all protein-synthesizing systems. Therefore the demonstration that suspensions of spermatozoa can incorporate radioa.ctive amino acids into their proteins (Bhargava., 1957; Bhargava., Bishop & Work, 1959b) was of interest. Martin & Brachet (1959), on the basis of microradioautographic studies, concluded that this incorporation did not actually take place in the spermatozoa but occurred in the cell debris or bacteria contained initially in the semen. Recent work (Abraham & Bhargava, 1963; P. T. Iype, K. A. Abraham & P. M. Bhargava, unpublished. work) has, however, demonstrated that the above mentioned incorporation occurs in the spermatozoa and represents synthesis of spermatozoal proteins; this work has also afforded an explanation for the negative findings of Martin & Brachet (1959). It therefore appeared to be of interest to re-investigate the reported absence of RNA from spermatozoa.

In most of the earlier experiments, the RNA estimations were made on small quantities of semen. In the investigation by Bhargava.et al., (l959a) the lower limit of detection of RNA in bull spermatozoa was 0.1 % of the deoxyribonucleic acid, of 0.033% of the dry weight of the cells. It therefore seemed possible that spermatozoa might contain a small amount of RNA, which could have escaped detection in earlier investigations with conventional analytical techniques. The presence of even traces of RNA in spermatozoa would be significant from the point of view of protein thesis by these cells. Recent investigations suggest that the code for the determination of the sequence of amino acids in a protein molecule is carried from the DNA in the form of a short-lived RNA, the ‘messenger RNA’ (Brenner, Jacob & Meselson, 1961; Gros et al. 1961). Both the ‘messenger RNA’ and the ‘soluble RNA’ (which is believed to carry the activated amino acids to the site of protein synthesis), are unlikely to represent more than a small fraction of the total RNA content of somatic mammalian cells .

This paper reports studies on the incorporation of radioactive precursors of nucleic acids into the total nucleic acid fraction of bovine spermatozoa; the effect of a few inhibitors on this incorporation has also been studied. These studies show the presence of minute quantities of a. metabolically active RNA in mature bovine spermatozoa. A preliminary communication based on this work has already appeared (Abraham & Bhargava, 1961).

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Nucleic acid metabolism of mammalian spermatozoa. K A ABRAHAM & P M BHARGAVA. Biochemical Journal, 1963, 86, 298-307.

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