HEREDITARY DEFECTS IN GALACTOSE METABOLISM IN ESCHERICHIA COLI MUTANTS, I. DETERMINATION OF ENZYME ACTIVITIES

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Abstract
A number of mutants of Escherichia coli K-12 strain, which are defective in galactose metabolism, have been identified as having single or multiple defects in the Leloir pathway. Enzyme assays for each step of this pathway have been described. Among the singly defective mutants found can be cited the galactokinase-less and galactose-1-phosphate uridyl transferase-less. A single mutant, lacking the uridine diphosphogalactose-4-epimerase, from a different E. coli strain (M strain) has also been described. The triply defective mutants (all K-12 strains) are geno-typically single mutants (Lederberg). An attempt to describe the triple defects as a result of a single defect of galactose permease is complicated by the fact that galactose, although unable to promote induction of any of the enzymes of the Leloir pathway, is able to elicit induction of [beta]-galactosidase. A hereditary block of galactokinase in 2 mutants of K-12 was found to be correlated with a synthesis of constitutive galactose-1-phosphate uridyl transferase. It seems, however, not possible to derive any correlation between the full constitutivety of galactose-1-phosphate uridyl transferase and the rate of formation of galactose-1-phosphate. Pleiotropism should be considered.