Nucleic acid metabolism of mammalian spermatozoa

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Abstract
The incorporation of [p32]phosphate, [8-C14]-adenine, [6-C14]orotic acid, [2-C14]thymlne and [2-C14]uracil in suspensions of washed buffalo and bull spermatozoa was studied. The first 3 of these precursors, but not thymine and uracll, are incorporated into the total nucleic acids of these spermatozoa. This incorporation was shown to be exclusively into RNA, which is present in these cells in amounts not exceeding 0.02% of their DNA. Chloramphenicol stimulates the incorporation of [P32]phosphate, [Cl4]adenine and [Cl4]orotlc acid into washed spermatozoa. Ribo-nuclease and a mixture of penicillin and streptomycin have no significant effect on this incorporation. Addition of free amino acids to the incubation medium results in a 2- to 3-fold increase in the incorporation of [p32]phosphate, [C14]adenine and [C14]orotic acid into washed spermatozoa. There is no significant loss of radioactivity from the nucleic acids on reincubation of washed P32-labelled spermatozoa in a medium containing a large excess of non-radioactive phosphate. [Cl4]Orotic acid is incorporated into washed spermatozoa at a much higher rate than in rat-testes homogenate. Seminal plasma inhibits the incorporation of nucleic acid precursors into spermatozoa. It is suggested that, during the incubation of washed bovine spermatozoa, there occurs a net synthesis of a functionally labile RNA.