Butanol extracts from myelin fragments: tryptamine binding to lipid fractions

To investigate the nature of the tryptamine binding components that originated from myelin butanol extracts (i.e., myelin proteolipids), the lipid mixtures obtained from these extracts were further fractionated by silicic acid column chromatography, and binding assays of 14C-tryptamine to those fractions were carried out by Sephadex LH20 column chromatography. Among several lipid fractions, only the F-C fraction retained the tryptamine binding properties of the original myelin butanol extracts, i.e., binding capacity, chromatographic profile and interaction with indoleamine analogues and other neurotransmitters. Since the quantitative TLC analysis indicated that this fraction contained a considerable amount of phosphatidylserine (PS) and phosphatidylinositol (PI), recombination experiments with these two acidic lipids were planned. The recombination system with PI did not show a tryptamine binding capacity, while the PS fraction possessed a tryptamine binding capacity similar to that of the myelin butanol extracts. However, displacement studies revealed that the recombinant fraction with PS alone did not display the complete regeneration of the specificity which had been observed in the myelin extracts. All these observations infer that the tryptamine binding components from myelin proteolipids are lipid in nature, and its binding entity is mainly PS. However, some specifically organized constitution with PS and other lipid molecule(s) may be necessary to regenerate the original tryptamine binding properties.