The extraction of intracisternal A-particles from a mouse plasma-cell tumor.

Abstract

Plasma-cell tumors in BALB/c mice contain numerous intracisternal A-particles which remain localized within microsomal vesicles when the tumor cells are disrupted by homogenization. Liberation of the particles has been achieved by subjecting microsome suspensions to mechanical shear in the presence of an optimal concentration of Triton X-100. The particles were concentrated by two cycles of sedimentation in sucrose-potassium citrate solutions, pH 7.2, and finally banded isopycnically in a sucrose density gradient containing dilute potassium citrate. Most of the particles were recovered in a density range of 1.20–1.24 gm/cu cm. A-particles extracted by this procedure retained their characteristic inner and outer shells. Electron microscopy of the gradient-isolated fractions revealed some residual contamination of the A-particles with microsomal membranes. The isolated material consisted of about 80% protein, 14% phospholipid (other lipids not studied) and 5 to 6% RNA. No DNA was detected. Deoxycholate treatment, which lysed the contaminating membranes and simultaneously stripped the A-particles of their outer shells, sharply reduced the phospholipid content of the fraction but did not remove RNA. Evidence is presented that 40 to 50% of the total RNA in the isolated fractions was contributed by other cytoplasmic components. The remainder may have represented RNA intrinsic to the A-particles themselves; however, further studies are required to establish this point.