The in vivo protein synthetic activities of free versus membrane-bound ribonucleoprotein in a plasma-cell tumor of the mouse

Ultrastructural analysis of membrane-bound polysomes in human myeloma cells

We prepared ultra-thin sections of human myeloma cells, in which the rER was cut tangentially, and studied the make-up and distribution of membrane-bound polysomes electromicroscopically. In IgG myeloma large and small polysomes were detected. The polysome distribution curve showed a high peak at 7 ribosomes and a lower peak at 17-18 ribosomes. IgA-, IgD- and IgE myeloma, as well as macroglobulinemia, showed peaks at 7 and 13 ribosomes. BJP myeloma manifested a sharp peak only at 7 ribosomes. Our results suggest that BJP myeloma has only small polysomes participating in L-chain synthesis, while the other myelomas exhibited large and small polysomes participating in H- and L-chain synthesis, respectively. The quantitative ratio of small and large polysomes was determined on the basis of an analytically corrected direct count.

Phospholipid synthesis and degradation during the life-cycle of P815Y mast cells synchronized with excess of thymidine

1. P815Y cells synchronized with excess of thymidine incorporate choline, proline and uridine throughout the cell cycle; the rate increases two- to four-fold during the S phase, when thymidine incorporation increases more than 15-fold. 2. Choline incorporated at any stage of the cell cycle turns over in a biphasic manner; stable and unstable components are each labelled maximally during the S phase. Total phospholipid also doubles predominantly during the S phase. 3. It is concluded that, despite turnover, choline incorporation is a useful measure of net phospholipid formation during the cell cycle.