Some studies on cellular fractions of the adductor muscle of Pecten maximus

Abstract

Summary The oxidative enzymes of subcellular fractions from the striated and smooth portions of the adductor muscle of Pecten maximus were studied. The investigation also included electron microscopic studies on tissue specimens and on the subcellular fractions. The concentration of mitochondria was low in both the types of muscles. Evidence was produced of an association of the fractions studied with the mitochondria of cells and what is described as “microsome” fractions. The difference spectra of the “mitochondrial” fraction (P10) of the striated adductor muscle revealed a set of cytochromes, essentially similar to those present in corresponding fraction of vertebrate cells. Treatment of this fraction with carbon monoxide produced spectral changes contributing further support to the occurrence of cytochrome a3. Cytochrome c was isolated from the striated adductor muscle. It was spectroscopically very similar to horse heart cytochrome c. The very weak difference spectrum of P10 of the smooth muscle was predominated by an absorption at 435 mμ. The difference spectra of the “microsome” fractions (P105) of the striated and smooth adductor muscles showed an insignificant absorption except for a distinct maximum at 432–435 mμ. The activities of various parts of the respiratory chain were determined. The subcellular fractions from the striated adductor muscle showed higher enzymic activities than the corresponding fractions from the non-striated adductor muscle. In all the tissue fractions studied the NADH-cytochrome c reductase activity predominated. P10 of the striated muscle showed relatively low rates of NADH and succinate oxidation compared with the NADH- and succinate-cytochrome c reductase and cytochrome c oxidase activities. This was taken to indicate a rate limiting step around cytochrome c in the electron transport chain. The role of these various enzymes in the overall functioning of the tissues is discussed.