ABSTRACT
The C20 polyunsaturated fatty acids (PUFAs), such as Mead acid (20:3n-9), dihomo-γlinolenic acid (DGLA, 20:3n-6), arachidonic acid (AA, 20:4n-6), and 5,8,11,14,17-ciseicosapentaenoic acid (EPA, 20:5n-3) (see Fig. 1 for structures and biosynthetic pathways), are of interest, as they are precursors for prostaglandins, thromboxanes, leukotrienes, prostacyclins, and so on, all of which have hormonelike activities. Possibly due to the physiological activities of these eicosanoids, PUFAs exhibit several unique biological activities, such as lowering of plasma cholesterol level, prevention of thrombosis, and so on. The inclusion of AA and 4,7,10,13,16,19-cis-docosahexaenoic acid (DHA, 22:6n-3) as supplements of infant formula has been recommended for the growth of preterm babies [1]. Also, EPA and DHA as dietary supplements has been recommended for the prevention of heart diseases [2], and γ-linolenic acid (18:3n-6) has been recommended for the relief of eczema [3]. Accordingly, PUFAs and/or lipids containing them are highly important substances in the pharmaceutical, medical, and nutritional fields. Because food sources rich in these PUFAs are limited to a few seed oils which contain 18:3n-6 and fish oil which contains EPA and DHA, recent investigations have been focused on microorganisms as alternative sources of these PUFAs.
