Use of 14CO2 ratios in metabolic assessment of human spermatozoa

Comparison of 14CO2 production for [1-14C], [2-14C] and [3-14C] pyruvate indicates the metabolic fate of pyruvate. Assuming that all pyruvate oxidized enters the TCA cycle via pyruvate dehydrogenase, the ratio of steady state 14CO2 production, [2-14C] pyruvate: [3-14C] pyruvate, determines the probability that specific citrate carbons will complete a turn of the TCA cycle. Comparing this probability and the 14CO2 production from [1-14C] pyruvate estimates the flux pyruvate to products derived from acetate that do not enter the TCA cycle. Data was collected for human sperm metabolizing glutamine and pyruvate over a four-hour period. The ratio of 14CO2 production, [2-14C] pyruvate: [3-14C] pyruvate even when correction was made for the fact that not all carbon derived from [2-14C] pyruvate that enters the TCA cycle is converted to CO2. 14CO2 production from [U-14C] glutamine was linear for glutamine concentration below 0.5 mM. In conclusion, CO2 ratios methods are applicable in metabolic analysis of small samples of human sperm where metabolite measurements are impractical