The enzymic properties of rat-liver nuclei. 1. Estimation of the extent to which contaminant material contributes to the activity observed in the nuclear fraction

Abstract

An attempt was made to determine whether the succinoxidase and aldolase activities of rat-liver nuclear fractions are due to the nuclei themselves or to contaminant material. The succinoxidase activity of nuclear fractions prepared by the method of Hogeboom et al (1952) was only 1.5% of the total in the homogenate and was only slightly higher than the percentage of unbroken liver cells in the nuclear fraction. Centrifuging the nuclear fraction in a medium of graded sucrose concentration revealed a complete absence of correlation between the distribution of succinoxidase and of nuclei along the length of the centrifuge tube. In 37 fractionations by the method of Hogeboom et al the nuclear fraction carried on the average 12.5% of the total aldolase activity of the liver homogenate, the enzyme being 1.44 times as concentrated in the nuclear fraction as in the original whole tissue. The aldolase activity of 7 different nuclear fractions was always greater than the succinoxidase and bore no constant relation to it. It is unlikely that fibrous material, erythrocytes, cytoplasmic particles and insufficient washing of the nuclei contribute significant amounts to the aldolase observed in the nuclear fraction. When the nuclear fraction was centrifuged in a medium of graded sucrose concentration a close correlation was observed between the distribution of nuclei and of aldolase along the length of the centrifuge tube. No correlation was observed between the distribution of unbroken liver cells and aldolase. Succinoxidase activity observed in the nuclear fractions seems due to contaminant material, but the aldolase is associated with the nuclei.