Multicompartmental distribution of ribonuclease II in mouse liver.

Thirty percent of RNase II (EC 3.1.27.5) is present in the cytosol of mouse liver where it exists in an inactive complex with a protein inhibitor. The remaining 70% of RNase II is active, soluble enzyme unassociated with inhibitor and is distributed in a ratio of 1.3 to 1 between the lumen of reticular elements and the interior of heavy particles. Although heavy particle RNase II resembles acid hydrolases in centrifugal behavior, in other tests including density shift experiments the resemblance is incomplete. In experiments employing lysis induced by L-amino acid methyl esters, RNase II activity is much more latent than the activity of the lysosomal marker, acid RNase. It is postulated that the heavy particle component of RNase II is contained in a secretory vesicle rather than in classic lysosomes.