INVESTIGATIONS INTO THE PRODUCTION OF LIPIDS BY SUBMERGED CULTURES OF THE MUSHROOM TRICHOLOMA NUDUM: II. STUDIES WITH UNIFORMLY LABELLED GLUCOSE
Tricholoma nudum mycelium, grown in a medium with a low nitrogen content, was adapted to a basal medium containing glucose and incubated with glucose-U-C14for 25 hours. The time – specific activity relations of the major fatty acids produced were determined for both the neutral lipids and the phospholipids. The results confirm a previous finding that in the phospholipids of T. nudum linoleic acid becomes labelled under the conditions used at almost the same rate as palmitic, stearic, or oleic acid, but that in the neutral lipids the specific activity of this acid initially lags considerably behind those of the latter three. It is postulated that this phenomenon is due to a difference in the relative sizes of the linoleic acid pools involved in the synthesis of the two lipid fractions. Only part of the material used for the formation of the fatty acids is derived directly from the substrate, the remainder apparently being provided by material already present in the mycelium. The various results, together with those of earlier workers, are critically evaluated, and it is concluded that the order in which fatty acids are labelled in tracer studies with intact cells is determined to a large extent by the conditions of the experiment and does not necessarily provide information on possible product–precursor relations.