| Abstract: | The presence and biosynthesis of the testis-specific isozyme of lactate dehydrogenase (LDH-X) in cells at various stages of spermatogenesis have been examined. Enrichment of testicular cells in various stages of spermatogenesis has been achieved by two methods: (1) cell separation by velocity sedimentation in the Elutriator rotor and (2) γ irradiation of testes to eliminate specific classes of testicular cells. Separation of cells from immature mice indicated that cells prior to the midpachytene stage contain no LDH-X. Measurement of LDH-X levels in cells separated from adult mice and in testicular homogenates prepared at various times after irradiation indicated that the highest level of LDH-X per cell (normalized for DNA content) was in spermatids. Synthesis of LDH-X was determined, after in vivo injection of 3H]valine, by measurement of the radioactivity in LDH-X precipitated with specific antiserum. After irradiation, the rate of LDH-X synthesis remained constant, despite the loss of early primary spermatocytes. In separated cells, the rate of LDH-X synthesis was highest in late pachytene spermatocytes, lower in round spermatids, and even lower, but still significant, in elongated spermatids. Therefore, the synthesis of LDH-X begins at a specific point during spermatogenesis, the midpachytene stage of spermatocyte development, and continues throughout spermatid differentiation. |
