Left- and right-handed helical tubule intermediates from a pure chiral phospholipid

Differential phase contrast microscopy under conditions of very slow coolin g reveals the dominant self-assembly mechanism of a chiral diacetylenic pho spholipid into multilamellar tubules to be the rapid growth of helical ribb ons from spherical multilamellar vesicles. Surprisingly. in the first secon ds of tubule formation, a purr enantiomer of 1,2-bis(10,12-tricosadjynoyl)- sn-glycero-3-phosphocholine [DC(8,9)PC] yields roughly equal numbers of lef t- and right-handed helices, inconsistent with the heretofore observed rela tionship between tubule helix handedness on phospholipid chirality. A much slower process follows by which tubules become multilamellar with a promine nt helical ridge upon the exterior. interestingly, these exterior helical r idges are of only a single handedness. [S1063-651X(99)01203-9].