Biosynthesis of docosahexaenoic acid (DHA, 22:6-4, 7,10,13,16,19): two distinct pathways

Docosahexaenoic acid (DHA) has long been recognized for its beneficial effect in humans, but its biosynthetic pathway has not been clearly established until recently. According to Sprecher, in mammals, DHA is synthesized via a retro-conversion process in peroxisomes-the aerobic delta4 desaturation-independent pathway. Recent identification of a Thraustochytrium delta4 desaturase indicates that delta4 desaturation is indeed involved in DHA synthesis in Thraustochytrium. More interestingly, an alternative pathway for DHA biosynthesis-the anaerobic polyketide synthase pathway was also reported recently to occur in Schizochytrium, another member of the Thraustochytriidae. This mini-review attempts to assess the latest research on these distinct pathways for DHA biosynthesis.