Alternate pathways of linolenic acid biosynthesis in growing cultures of Penicillium chrysogenum

Evidence was obtained that Penicillium chrysogenum can produce linolenate by two biosynthetic pathways, i.e., by elongation of a shorter trienoic acid as well as direct desaturation of 18-C acids. In oxygen deficient cultures, exogenous hexadecatrienoate stimulated 1-¹⁴C]acetate incorporation into labeled octadecatrienoate and U-¹⁴C]hexadecatrienoate with nonlabeled acetate yielded linolenate that had relatively little label in the 1-C position. With 1-¹⁴C]acetate as the only added substrate, oxygen deficiency inhibited incorporation of label into monoenoic and dienoic acids but not into trienoic acids. Incorporation of the U-¹⁴C]linoleate into linolenate also was inhibited.In aerated cultures, 1-¹⁴C-label from laurate, palmitate, stearate, oleate, linoleate, and hexadecatrienoate was readily incorporated into linolenate. Decarboxylation and oxidation studies indicated that the longer acids were incorporated largely intact. U-¹⁴C]Linoleate was incorporated into linolenate in which the fraction of label in 1-C was similar to that of the substrate. These data suggest that this mold has broader synthetic capabilities than do some chloroplast systems for the biosynthesis of linolenate.