Developmental Changes in Rat Liver Xanthine Oxidase(s) and Its Intracellular Distribution

Developmental change and subcellular distribution of xanthine oxidase in the rat liver were examined. The specific activity of the fetal liver xanthine oxidase increased sharply to the levels of the adult liver on the day of the birth. After birth, the activity dropped rapidly and on the 14th day after birth it was about 1/4 of adult level. Then the activity was regained and around 28th day after birth it was about the same as in adult level. In the livers from 80 days old rats, about 60% of total xanthine oxidase activity was found in soluble fraction and the rest was distributed among particulate fractions including microsomal, lysosomal, mitochondrial and nuclear fractions. In contrast to the adult livers 80%. of total xanthine oxidase activity in fetal liver was found to be in particulate fractions. From kinetic studies of xanthine oxidases in particulate and soluble fractions it was suggested that xanthine oxidase in soluble fraction and xanthine oxidase in particulate fraction might be different in their natures of protein molecule.