PURIFICATION AND CHARACTERIZATION OF A NOVEL ISOPROPANOL DEHYDROGENASE FROM PHYTOMONAS SP

An alcohol dehydrogenase with two identical subunits and a subunit mol ecular mass of 40 000 was purified from Phytomonas sp. isolated from t he lactiferous tubes of Euphorbia characias. Digitonin titration and s ubcellular fractionation suggest that the enzyme is present in the mit ochondrion. It utilises as substrates, primary and secondary alcohols, is specific for NAD(+) as coenzyme and is inhibited by HgCl2. The pH optimum for the oxidation of ethanol is 9.5, and for the reverse react ion 8.5. The apparent K-m values for iso-propanol and ethanol are 40 a nd 34 mu M, respectively and for the reverse reaction, with acetone as substrate, 14 mu M. The respective specific activities with iso-propa nol and ethanol as substrate, as measured in crude extracts are 300 an d 16 mU (milligram of protein)(-1). In isoelectric focusing the enzyme showed three major bands with slightly differing isoelectric points t hat ranged from 6.4 to 6.8. The name, iso-propanol dehydrogenase is pr oposed for this enzyme. (C) 1997 Elsevier Science B.V.