Iodoacetic‐Acid‐Resistant Alcohol Dehydrogenase of an Escherichia coli Mutant

Nitrosoguanidine‐induced mutants of Escherichia coli were tested in vivo (tetrazolium staining assay) for iodoacetic acid resistance of their alcohol dehydrogenase. One mutant was isolated (mutant 2773) which has a fully iodoacetic‐acid‐resistant alcohol dehydrogenase. Mutant 2773 contains two species of alcohol dehydrogenase; one (the enzyme of the mutant strain, wild‐type fraction i.e. wild‐type‐mutant enzyme) has the same characteristics as the enzyme of the parental strain (wild‐type enzyme), including the inhibition by iodoacetic acid; the other species (enzyme of the mutant strain, mutant fraction i.e. the mutant enzyme) however, is iodoacetic acid resistant, has a high molecular weight (> 600000) and is not related to the wild‐type enzyme as detected by immunological methods. The role of SH‐groups taking part in the reaction at the active center of the alcohol dehydrogenase and the occurrence of several enzyme species are discussed.