CHARACTERISTICS AND EFFICIENCY OF GLUTAMINE PRODUCTION BY COUPLING OFA BACTERIAL GLUTAMINE-SYNTHETASE REACTION WITH THE ALCOHOLIC FERMENTATION SYSTEM OF BAKERS-YEAST

Glutamine production with bacterial glutamine synthetase (GS) and the sugar-fermenting system of baker's yeast for ATP regeneration was inve stigated by determining the product yield obtained with the energy sou rce for ATP regeneration (i,e,, glucose) for yeast fermentation. Fruct ose 1,6-bisphosphate was accumulated temporarily prior to the formatio n of glutamine in mixtures which consisted of dried yeast cells, GS, t heir substrate (glucose and glutamate and ammonia), inorganic phosphat e, and cofactors. By an increase in the amounts of GS and inorganic ph osphate, the amounts of glutamine formed increased to 19 to 54 g/liter , with a yield increase of 69 to 72% based on the energy source (gluco se) for ATP regeneration. The analyses of sugar fel mentation of the y east in the glutamine-producing mixtures suggested that the apparent h ydrolysis of ATP by a futile cycle(s) at the early stage of glycolysis in the yeast cells reduces the efficiency of ATP utilization. Inorgan ic phosphate inhibits phosphatase(s) and thus improves glutamine yield . However, the analyses of GS activity in the glutamine-producing mixt ures suggested that the higher concentration of inorganic phosphate as well as the limited amount of ATP-ADP caused the low reactivity of GS in the glutamine-producing mixtures, A result suggestive of improved glutamine yield under the conditions with lower concentrations of inor ganic phosphate was obtained by using a yeast mutant strain that had l ow assimilating ability for glycerol and ethanol. In the mutant, the a ctivity of the enzymes involved in gluconeogenesis, especially fructos e 1,6-bisphosphatase, was lower than that in the wild-type strain.