Other yeast fatty acids

Although production of yeast lipids as a source of triacylglycerol oils is limited to oleaginous species (Table 9.2), there are several other potentially useful lipid types produced by yeasts. These, however, do not represent alternatives to plant seed oils but are mainly for technical applications within the oleochemical industry. As this area is strictly outside the scope of this book, these alternative yeast lipids are described only briefly. 

In Candida bogoriensis, the hydroxy fatty acid is 13-hydroxydocosanoic acid, also attached to sophorose. 

Other glycolipids found in yeasts grown on alkanes include a di-acylated mannosylerythitol (see Ratledge and Evans, 1989). Small amounts of acylated glucoses and galactoses have also been found in baker s yeast Saccharomyces cerevisiae). 

Industrial applications of the glycolipids are limited although the sophorolipid of C. bombicola was reported to be in commercial production by Kao Corporation of Japan as a component of some cosmetics (Inoue, 1988) it is uncertain if this still continues. 

For readers requiring further details of the role and nature of biosurfactants, the recent monograph edited by Kosaric (1993) should prove to be comprehensive. Other minor yeast lipid components have been covered in the review by Ratledge and Evans (1989). These include the 

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There is considerable interest in the role of formic acid and other volatile fatty acids in the early diagnosis of organic matter in lacustrine and marine sediments. Formic acid is an important fermentation product or substrate for many aerobic and anaerobic bacteria and for some yeasts, hi the atmosphere, formic acid is an important product in the photochemical oxidation of organic matter. 

Malonyl CoA, labeled with in the methylene carbon, is used in excess as a substrate in a system in vivo for the synthesis of palmitoyl CoA, which is catalyzed by a yeast fatty acid synthase complex. Acetyl CoA and other substrates are also present in the system, but acetyl CoA carboxylase is not. Which carbons in palmitoyl CoA vrill be labeled ... 

Saccharomycodes and Hanseniaspora (but not Hansenula) are devoid of 18 2 and all other polyunsaturated fatty acids. Claims to have detected 18 2 in these yeasts (see lists in Rattray, 1988) are usually unsubstantiated and can be attributed to the inclusion of plant extracts in the growth medium. Even yeast extract may contain small amounts of 18 2 residues arising from the original yeast (usually brewer s yeast) growing on wort which is itself derived from barley. 

The synthesis of y-DL is the most prominent example for the microbial production of fragrance lactones. Nevertheless, the biotransformation route via P-oxidation and lactonization (Fig. 1) in yeast can be applied for the production of several lactones provided that a suitable hydroxy fatty acid as starting material is available. For example, ricinoleic acid, the starting compound for the production of y-DL, can be isolated in large quantities from castor oil. However, other hydroxy fatty acids are more difficult to obtain. For instance, researchers from Takasago International Corporation reported the conversion of 11-hydroxy palmitic acid ethyl ester to 8-decalactone by the yeast Candida sorbophila (Mitsuhashi and limori 2004). 0.13 g substrate in 30 itiL culture medium yielded 0.019 g 8-decalactone in 96 % ee optical purity after 11 days. 

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

The structure of mannose-rich polysaccharide core in GL4 is close to that of yeast mannan (from Saccharomyces cerevisiae), which was inactive for IL-6 induction in a human peripheral whole-blood cells test system. This fact suggests that not the mannose moieties but other components, such as the lipophilic moiety and/or phosphates, are important for the activity. The lipophilic products in HF-hydrolysate of GL4 were then analyzed. In addition to peaks corresponding to the known fatty acids (C16 0, C18 1), two other unknown ion peaks at m/z 330 and 356 were found by FAB-MS (data not shown). 

Pantothenic acid (8.48), a hydroxyamide, occurs mainly in liver, yeast, vegetables, and milk, but also in just about every other food source, as its name implies [pantos (Greek) = everywhere]. It is part of coenzyme A, the acyl-transporting enzyme of the Krebs cycle and lipid syntheses, as well as a constituent of the acyl carrier protein in the fatty-acid synthase enzyme complex. 

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