Endo-I,4-fI-glucanase and xylanase were produced by Trichodenna reesei immobilized on polyurethane foam using lactose as the main carbon source. The most porous carrier was found to be the best of those tested. The nitrogen source and KHzPO, concentration of the production medium had a marked effect on culture pH during the course of fermentation and, consequent&, on xylanase activity. An increase in lactose concentration from 7 to 27 gll resulted in an increase in endoglucanase activity (max. 730 VJml). xylanase activity (max. 3350 U/ml) and filter paper activity (max. 3.0 FPUIml).

The activity of esterase in baker's yeast cells and in cell fractions was estimated using 2-oxoglutaric acid diethyl ester, p-nitrophenyl acetate and a-and p-naphthyl acetate as substrates.The esterase hydrolysing 2-oxoglutaric acid ester was shown to be located inside the cell, both directly by an enzymic method and by indirect evidence. The activities of the esterases hydrolysing aryl esters were found to vary greatly with the different substrates and estimation methods used. The presence of esterase activity towards phenyi and naphthyl esters in both cell wall digests and sphaeropiast lysates confirms the localization of at least one esterase in both sides of the plasma membrane barrier. Depending on the method of evaluation, values between 80 and 40% of the total were obtained for the proportion of esterase activity located outside the plasma mem brane, the most reliable values being about 50-65%.

Ethyl esters of fatty acids (C,-C,,), isoamyl acetate and 2-phenethyl acetate were studied as sub strates for yeast esterases and compared with the synthetic substrates, p-nitrophenyl esters and P-naphthyl esters. Intact yeast, the 55% and 55-75% ammonium sulphate precipitate of centrifuged yeast homogenate, and partly purified esterases were used for the determination of the hydrolysation activity towards the esters.The results showed that the yeast esterases prefer to hydrolyse the ethyl esters with acyl chain length of Cs to C,,. The acetate esters, ethyl acetate, isoamyl acetate and 2-phenethyl acetate are only very slowly hydrolysed or remain unaffected. The substrate specificity of different esterases varies and can be used for their characterisation.Investigating pH optimum curves using intact yeast and a crude esterase preparation and different substrates confirmed the earlier result that there are esterases on both sides of the plasma mem brane. The specificity of intracellular and periplasmically located esterases is, however, different.

Ester/acid equilibria were studied in reaction mixtures containing ethyl alcohol, ethyl caprylate or oaprylic acid, and baker's yeast or an esterase purified from baker's yeast in buffer. The equi librium concentration of ethyl caprylate after an incubation of yeast or a yeast esterase preparation with caprylic acid was the same as in the case where yeast or esterase preparation was incubated with the ethyl caprylate. The equilibrium attained depends not only on the concentration of the ester and the alcohol but also on the pH, the final ester concentration remaining higher at low pH. It could be shown that yeast esterase is responsible for the hydrolysis or synthesis of the ester. At equilibrium the molar ratio of ethyl caprylate/caprylic acid is about the same as that found in fermentation solutions under the same conditions.

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