Commentary on ‘Effects of acetylcholine on the turnover of phosphoryl units in individuals phospholipids of pancreas slices and brain cortex slices’ by L.E. Hokin and M.R. Hokin Biochim. Biophys. Acta 18 (1955) 102–110

Abstract

The incorporation of 32P has been followed in five individual phospholipid types in slices of pigeon pancreas and guinea pig brain cortex, incubated in the presence and absence of acetylcholine. In pancreas slices the average 32P-specific activities of the individual phospholipids show the following increases after incubation with acetylcholine (10−3M) as compared with the control: phosphatidyl choline 73%, phosphatidyl ethanolamine 75%, phosphatidyl serine 293%, phosphoinositide 1093%, “phosphatidic acid” 50%. The increase in radioactivity of phosphoinositide accounts for about 75% of the increase in radioactivity of the “total phospholipid phosphorus”. In brain cortex slices acetylcholine (10−2M) stimulates 32P incorporation into diphosphoinositide and “phosphatidic acid” by about 100% and into phosphatidyl choline by about 50%. The incorporation of 32P into phosphatidyl ethanolamine and phosphatidyl serine under these conditions is too low for the slight increases to be regarded as significant. The incorporation of ethanolamine-2-14C into phosphatidyl ethanolamine and phosphatidyl choline was followed in pancreas slices incubated in the presence and absence of acetylcholine (10−3M). Acetylcholine stimulates the incorporation of 14C into these phospholipids to approximately the same extent as it stimulates the incorporation of 32P. This suggests that acetylcholine stimulates the turnover of phosphorylcholine and phosphorylethanolamine as units in their respective phospholipids. The rates of incorporation of glycerol-1-14C into the various phospholipids of brain cortex slices are approximately the same, indicating that the total synthesis (or total turnover) of each of these phospholipids is of the same order of magnitude. The rates of 32P incorporation into the various phospholipids in this tissue are highly disproportionate, suggesting that most of the incorporation of 32P into the different phospholipids may be due to the same type of independent turnover of phosphoryl moieties as that which is found in the presence of acetylcholine.