Abstract:
Boar sperm oxidatively metabolized fructose, glucose, glycerol, glycerol3-phosphate and lactate to CO<emph type="8">2 but pyruvate producedonly small amounts of CO<emph type="8">2 and this was almost completelyprevented when endogenous glycolytic metabolism was inhibited. Lactate was thepreferred substrate over fructose, glycerol and glycerol 3-phosphate and whenlactate was offered in the presence of pyruvate, lactate was preferentiallyoxidized to CO<emph type="8">2. The rate of oxidation of fructose,glycerol and glycerol 3-phosphate was approximately halved in the presence ofequi-molar concentrations of lactate and the metabolism of lactate wasprogressively decreased in the presence of increasing concentrations ofmersalyl, an inhibitor of lactate transport. Sperm maintained a high energycharge potential when incubated with lactate as substrate in the presence orabsence of bromopyruvate, an inhibitor of endogenous glycolytic metabolism.This evidence confirms that it is lactate, rather than pyruvate, that entersthe mitochondria thereby constituting a lactate-pyruvate transportsystem in these cells for regenerating cytoplasmic nicotinamide adeninedinucleotide (NAD <emph type="7">+). Electrophoretic examination of thelactate dehydrogenase isozymes from sperm and several other tissues of theboar showed that sperm contained almost entirely an isozyme which was notpresent in the other tissues.