ADDITIONAL GPI-ANCHORED GLYCOPROTEINS ON HUMAN PLATELETS THAT ARE ABSENT OR DEFICIENT IN PAROXYSMAL-NOCTURNAL HEMOGLOBINURIA

In order to detect novel glycophosphatidylinositol (GPI)-anchored plat elet proteins, human platelets were incubated with PI-specific phospho lipase C (PI-PLC) and the supernatant was analysed by PAGE and silver- staining for additional protein bands. PI-PLC treatment resulted in th e appearance of at least two additional novel GPI-linked glycoproteins (GP), GP500 and GP175, in the supernatant. Their presence on the plat elet plasma membrane surface was demonstrated by periodate/[H-3]borohy dride surface-labelling. Activation of platelets did not enhance the a mount of GP500 and GP175 that could be cleaved by PI-PLC. In Triton X- 114 phase partitioning of platelet membranes the membrane form of GP17 5, mfGP175, was in the Triton phase while mfGP500 was found in the wat er phase. Neither GP500 nor GP175 were present in the supernatant of s urface-labelled platelets treated with PI-PLC from 4 patients, diagnos ed as having paroxysmal nocturnal haemoglobinuria (PNH), but the super natant from platelets from healthy volunteers treated the same way con tained both.