Formation of Esters by Yeast. II. Investigations with Cellular Suspensions of Hansenula Anomala

Open Access
Publisher Website
Google Scholar
Abstract
Using cellular suspensions of Hansenula anomala with ethanol as substrate, the optimum pH for ester accumulation was found to be between 2.1 and 2.6. The high accumulation of ethyl acetate at low pH is in part due to the inhibition of esterase activity. At pH 2.1, acetic acid was found to be toxic at concentrations ranging from 0.01 [image] to 0.05 [image]. At pH 6.7, on the other hand, cellular suspensions produced 70 m[image] of acetate per liter from ethanol without apparent toxic effect and could oxidize added acetate in concns. as high as 0.3 [image]. Although only trace amounts of ester were formed from ethanol at pH 6.7, the addition of DFP, a specific inhibitor, resulted in a significant accumulation of ester at this pH, suggesting that ethyl acetate may be formed and then rapidly hydrolyzed by the cells at pH 6.7. Formation of esters from propanol, butanol, and amyl alcohol could not be detected. From the high yields of ester formed, the experiment with DFP at pH 6.7 and the observation that ester formation is linked to respiration, it is evident that ethyl acetate formation by H. anomala is most probably an energy coupled reaction and is not the result of a reversal of a simple hydrolysis mediated by an esterase. Attempts to obtain an active cell-free preparation which synthesizes ester were unsuccessful. A major difficulty was the presence of the esterase in these extracts.