The appearance, disappearance and reappearance of plasmalogens in evolution.

Plasmalogens, 1-O-alk-1'-enyl 2-acyl glycerol phospholipids and glycolipids, seem to have evolved first in anaerobic bacteria, but they did not persist when facultative and aerobic species appeared after the concentration of oxygen increased in the early earth's history. Later, when aerobic animal cells appeared with their mitochondria and other intracellular organelles, plasmalogen biosynthesis requiring molecular oxygen, reappeared. The possible reasons for the disappearance and reappearance of plasmalogens in the evolution of life on earth are discussed. The sensitivity of plasmalogens to reactive oxygen species may have caused their disappearance when respiration first evolved. Special features of plasmalogen structure and the resulting lipid packing may account for their reappearance.