Nonlysosomal cytoplasmic degradation.

Several types of cytoplasmic and nuclear inclusions represent stages in the process of non-lysosomal cytoplasmic degradation. Nonlysosomal degradation takes place in regions where cytoplasmic components are trapped and not accessible to primary and secondary lysosomes. Such trapping occurs within the lumina of the nuclear envelope and of endoplasmic reticulum in the form of inverted vesicles, within the nucleus, within mitochondria and within cavities formed by the process of topolysis in neutral lipid droplets. The concept of the process of nonlysosomal degradation permits dynamic interpretation of various inclusions as the concept of the process of focal cytoplasmic degration (autophagy) leads to dynamic interpretation of the lysosome.

Isolation and partial characterization of high-density lipoprotein HDL1 from rat plasma by gradient centrifugation.

The lipoproteins isolated from rat plasma by flotation in the density range 1.019-1.063 g/ml were further characterized. Using rate zonal ultracentrifugation, we isolated two lipoproteins in almost equal proportions from this density range. Similar isolations may be accomplished with density gradients in a swinging-bucket rotor. On isopycnic-density-gradient ultracentrifugation one component banded at rho = 1.031 g/ml and the other at rho = 1.054 g/ml. More that 98% of the apoprotein of the lighter component was B protein, and hence this particle is LD (low-density) lipoprotein. Of the apoproteins of the rho = 1.054 g/ml particles, designated lipoprotein HDL1, over 60% was arginine-rich peptide, and the remainder was A-I, A-IV and C peptides. The molecular weight of these lipoproteins determined by agarose column chromatography was 2.36 x 10(6) for LD lipoprotein and 1.30 x 10(6) for lipoprotein HDL1. On electron microscopy the radius of LD lipoprotein was 14.0 nm and that of lipoprotein HDL1 was 10.0 nm, in contrast with molecular radii of 10.4 nm and 8.4 nm respectively determined from the gel-permeation-chromatography data. The lipid and phospholipid composition of both particles was determined. Lipoprotein HDL1 was notable for both the concentration of its esterified cholesterol, which was similar to that of LD lipoprotein, and the low triacylglycerol content, resembling that of HD lipoprotein. The possible origin of lipoprotein HDL1 is discussed.