AJP - Cell Physiology, Vol 245, Issue 1 52-C60, Copyright © 1983 by American Physiological Society
Role of particle interaction on distribution of liver lysosomes in colloidal silica
C. A. Surmacz, J. J. Wert Jr and G. E. Mortimore
Rat liver mitochondrial-lysosomal fractions were separated on gradients of
colloidal silica. Lysosomal enzymes were distributed bimodally. The dense
peak (1.117 g/ml) was nearly free from contaminants;
beta-N-acetyl-D-glucosaminidase was enriched nearly 60-fold. By contrast,
the buoyant peak (1.085 g/ml) co-sedimented with mitochondria, microsomes,
peroxisomes, and Golgi particles. Decreasing the amount of protein layered
on the gradient medium or dispersing a full sample through it shifted
lysosomal marker from the buoyant to the dense peak. Thus the majority of
lysosomes in the two peaks appeared to have equivalent densities. Electron
microscopic examination of particles separated from gradients with layered
samples showed that the dense peak contained most of the dense bodies,
whereas the buoyant peak was relatively enriched in autophagic vacuoles.
Dispersion, however, shifted autophagic vacuoles from the buoyant to the
dense peak without affecting the distribution of dense bodies. We conclude
that the bulk of buoyant particles act as a sieve to retard the density
equilibration of autophagic vacuoles without specifically affecting other
lysosomal enzyme-containing components.
