Effect of Triton X-100 on Electrophoretic Mobility of Red Blood Cell Ghosts from Normal Individuals and Patients With Tay—Sachs Disease

The negative surface charge of red blood cell ghosts and their anodal electrophoretic migration are largely due to their sialic acid moiety. The RBC of patients with Tay—Sachs disease are thought to contain increased amounts of sialic acid. Electrophoretic mobility and ganglioside content of RBC ghosts were compared in four patients with Tay—Sachs disease and eight normal controls. There was no measurable difference in electrophoretic mobility on cellulose acetate or acrylamide gel. The sialic acid content of lyophilized RBC ghosts was about the same for samples from both patients and controls. The nonionic detergent, Triton X-100, interacts with the ghost glycolipoprotein, causing a reversal of migration, both on cellulose acetate and moving-boundary electrophoresis. Acrylamide gel, by its sieving effect, disrupts the complex, which then migrates anodally again.

Increased synthesis of phospholipid during phagocytosis

Incorporation in vitro of (32)P-labeled lysolecithin (LPC) or lysophosphatidylethanolamine (LPE) into respectively lecithin (PC) and phosphatidylethanolamine (PE) of rabbit granulocytes and alveolar macrophages was compared in the absence and in the presence of ingestible particles. Maximal synthesis of PC by intact cells occurred at added LPC concentrations of less than 0.05 mmole/liter, i.e., at levels found in plasma. Accumulation of PC-(32)P proceeded linearly for at least 30 min and varied directly with cell concentration. While per cell granulocytes and macrophages converted comparable amounts of medium LPC to cellular PC, per milligram of protein, the granulocytes were approximately four times more active than the much larger macrophages. After 30 min newly synthesized PC-(32)P represented as much as 5% of total granulocyte PC. For macrophages this fraction did not exceed 1%. Addition of polystyrene or zymosan particles to the cell suspension resulted in up to 3-fold stimulation of incorporation of LPC-(32)P or LPE-(32)P into their respective diacyl derivatives. This stimulation did not occur when the cells were homogenized. Breakdown of LPC to water-soluble products during phagocytosis of polystyrene particles was the same as at rest. By use of doubly labeled LPC, the mechanism of PC synthesis by the two cell types has been identified as direct acylation of medium LPC, both at rest and during engulfment. Evidence presented in the case of granulocytes suggests that the increased translocation of medium LPC-(32)P during phagocytosis and its conversion to PC represents net synthesis. The findings indicate that LPC, a normal constituent of plasma, can serve as substrate in PC synthesis by phagocytic cells. This mechanism of PC synthesis can account for appreciable addition of membrane PC, especially by granulocytes. It is proposed that stimulation of this pathway provides building blocks for increased membrane formation during phagocytosis.