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Carbon Dioxide Fixation by Bovine Semen, Washed Spermatozoa, and Seminal Plasma¹

Department of Dairy Science, The Pennsylvania State University, University Park 16802

ABSTRACT

Radioactive carbon dioxide, released by acidifying NaH¹⁴CO₃ in a side arm of a Warburg flask, was incorporated by whole semen, washed spermatozoa, and seminal plasma. When the incubation mixture was fractionated into supernatant, total lipids, nucleic acids, and protein, radioactivity was recovered in both the supernatant and total lipid fractions of whole semen but only in the supernatant of washed spermatozoa. Fixation of ¹⁴CO₂ by washed spermatozoa was significantly less in Krebs-Ringer-phosphate buffer, pH 7.4, than in Krebs-Ringer buffer, pH 7.4. When pyruvate was not added, there was little or no CO₂ fixation by washed spermatozoa; however, substantial ¹⁴CO₂ incorporation occurred in the presence of 15mM pyruvate. Increasing pyruvate above 15mM resulted in no significant additional increase in CO₂ fixation. Malic enzyme activity was found in acetone powder extracts of washed bovine spermatozoa, and NADP⁺ and MnCl₂ were required for maximal activity.

¹ Authorized for publication as Paper 3851 in the Journal Series of the Pennsylvania Agricultural Experiment Station. Supported in part by Public Health Service Grant HD 00039-06.