Alcohol Acetyltransferase Activity Research Articles

低アルコール清酒用酵母の造成

The protoplast fusion between sake yeast Kyokai No.7 strain (K-7) and adenineless strain of sake yeast Kyokai No.10 was carried out to breed sake yeasts for making sake with low alcohol content. Four nuclear fusant strains were obtained as judged from cell size, nuclear DNA content and chromosomal band patterns in pulse field gel electrophoresis. The specific growth rate of these strains in yeast extract-polypeptone-glucose (YEPD) medium at 1° was intermediate between those of parent strains. But alcohol acetyl transferase activities (estimated from the formation of iso-amyl acetate/108cells) of these strains were 2-3 times those of parent strains. The time course of fermentation during small-scale low alcohol sake making using fusant strains showed slower rate than that of the parent K-7 strain. The resulted sake by fusant strains contained more amino aids and reducing sugar than that made by K-7 strain, and the former had better sensory peculiarity than the latter.

糖化酵素を用いた芋焼酎製造における香味成分の検討

The shochu made from cooked sweet potato using a saccharifying enzyme was a new type one, but its taste lacked smoothness. To improve the taste, fermentation tests were done by the same method as in the previous paper except for the use of shochu yeast, SZ.The fermentation was terminated after 48 hr at 27°C with the enzyme concentration of 30 Ufg total sugar, but the shochu made from the mash fermented for 72 hr lacked smoothness, either.Main flavor components produced were n-propyl, i-butyl, and i-amyl alcohols, and their formation could be explained by the over flow theory in the amino acid biosynthetic pathway, which was proved by fermentation tests using an auxotroph of Saccharomyces cerevisiae, HM 2 (Ile-, Val-).However, the concentration of isoamyl acetate was low, being 3.2 mg//. The concentration of isoamyl alcohol was almost the same as compared with that produced by Kyokai 7 and 701, but the activity of alcohol acetyltransferase (A ATase) was only one forth that of the latters.Ethyl stearate, ethyl oleate and ethyl linoleate in shochu made from the fermented mash were also much less than those in shochu made by the conventional method with rice koji. Then, fermentation of cooked sweet potatoes by adding either cooked or raw rice was done under the same conditions, resulting in an increase of isoamyl acetate and ethyl esters of higher fatty acids in shochu, which made the taste smoother. The shochu made by this method is a new type one with good flavor and satisfactory smoothness.

Cell-free synthesis of ethyl hexanoate by extract from Neurospora sp., containing a novel acyl coenzyme A: Alcohol acyltransferase.

New acyl coenzyme A: alcohol acyltransferase activity was found in the cell-free extract of Neurospora sp. ATCC 46892 which produces ethyl hexanoate abundantly in its culture broth. This enzyme catalyzed the esterification between ethanol and «-hexanoyl coenzyme A. It also acted on /i-butyryl coenzyme A, but not on acetyl coenzyme A. It was detected mostly in the cytoplasm. The activity was accelerated by high concentrations of sodium chloride, and unsaturated fatty acid did not inhibit it. This enzyme played a major role in biosynthesis of ethyl esters which were formed with ethanol and higher acyl coenzyme As. This is the first report of an alcohol acyltransferase which does not have alcohol acetyltransferase activity.

Ester Formation by Brewers’ Yeast during Sugar Fermentation

Formation of acetate esters by brewers’ yeast during sugar fermentation was investigated in relation to alcohol acetyltransferase activity influenced by the fatty acid composition of the yeast cell membrane. Glucose gave more acetate esters with a higher activity of alcohol acetyltransferase than the other carbohydrates. When maltose was fermented, the activity of alcohol acetyltransferase bound to the cell membrane was suppressed by unsaturated fatty acids accumulated in the cell membrane and the formation of acetate esters was greatly reduced without insufficient fermentation. On the other hand, when fructose was fermented, the ester formation was reduced with a decrease in the enzyme activity and the formation of higher alcohols through insufficient

Ester formation by brewers' yeast during sugar fermentation.

Formation of acetate esters by brewers’ yeast during sugar fermentation was investigated in relation to alcohol acetyltransferase activity influenced by the fatty acid composition of the yeast cell membrane. Glucose gave more acetate esters with a higher activity of alcohol acetyltransferase than the other carbohydrates. When maltose was fermented, the activity of alcohol acetyltransferase bound to the cell membrane was suppressed by unsaturated fatty acids accumulated in the cell membrane and the formation of acetate esters was greatly reduced without insufficient fermentation. On the other hand, when fructose was fermented, the ester formation was reduced with a decrease in the enzyme activity and the formation of higher alcohols through insufficient

Cellular Fatty Acid and Ester Formation by Brewers′ Yeast

The activity of alcohol acetyltransferase, bound to the cell membrane and responsible for the formation of acetate esters, was affected by the fatty acid composition of the cell membrane. When saturated fatty acids, which only slightly inhibit alcohol acetyltransferase activity, were in-corporated into the cell membrane, the enzyme activity and ester formation were only slightly affected. On. the other hand, when unsaturated fatty acids, which strongly inhibit the enzyme activity, accumulated in the cell membrane, ester formation was suppressed with inhibition of the enzyme activity. The mechanism of formation of acetate esters by brewers′ yeast was explained by the alcohol acetyltransferase activity under the influence of the fatty acid composition of the cell membrane.

Cellular fatty acid and ester formation by brewers' yeast.

The activity of alcohol acetyltransferase, bound to the cell membrane and responsible for the formation of acetate esters, was affected by the fatty acid composition of the cell membrane. When saturated fatty acids, which only slightly inhibit alcohol acetyltransferase activity, were incorporated into the cell membrane, the enzyme activity and ester formation were only slightly affected. On. the other hand, when unsaturated fatty acids, which strongly inhibit the enzyme activity, accumulated in the cell membrane, ester formation was suppressed with inhibition of the enzyme activity. The mechanism of formation of acetate esters by brewers' yeast was explained by the alcohol acetyltransferase activity under the influence of the fatty acid composition of the cell membrane.