Biochemical Characterization of Boar Sperm Cytochrome Oxidase
Cytochrome oxidase was isolated from boar sperm midpieces by extraction and fractionation with ammonium sulfate in the presence of cholate. The enzyme was further purified to apparent homogeneity by the DEAE-cellulose column chromatography in the presence of 0.3% Triton X-100.
The purified enzyme exhibited oxidized and reduced optical spectra similar to those of the bovine heart and rat liver cytochrome oxidases. However, the sperm oxidase was found to contain much higher amounts of subunits I,II and III than the other smaller subunits. Interestingly, we found that the sperm oxidase was much more acid-stable than the bovine heart and rat liver counterparts. The optimum pH for the sperm oxidase catalyzing the electron transfer from ferrocytochrome c to cytochrome a was around pH 4.8, and those for the bovine heart and rat liver were 6.2 and 6.8 respectively. In addition, we found that Ca2+ ion (10-100 μM) inhibited the activity of the sperm oxidase, whereas stimulated those of the bovine heart and rat liver enzymes.
The peculiar properties of sperm cytochrome oxidase may be due to the fact that the well-packed chromosomes in the sperm headpiece do not function so that the nuclear gene-coded subunits are deficient in the sperm cytochrome oxidase. The finding that the sperm oxidase was more acid-stable is an example of structure-function coordination, and will be discussed from the viewpoint of chemiosmotic theory and the unique structure and functions of the sperm mitochondria.
KeywordsAmmonium Sulfate Cytochrome Oxidase Intermembrane Space Bovine Heart Cytochrome Oxidase Activity
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