Proline biosynthesis in Escherichia coli. Purification and characterisation of glutamate-semialdehyde dehydrogenase.

Glutamate-semialdehyde dehydrogenase, catalysing the reduction in vivo of gamma-glutamyl phosphate to glutamate 5-semialdehyde in the pathway of proline biosynthesis in Escherichia coli, has been purified to homogeneity. High initial levels of the enzyme were achieved by using a multicopy ColEl-pro A, B hybrid plasmid. The protein has a molecular weight of 1.89 X 10(5) and consists of four identical subunits of molecular weight 4.7 X 10(4) each. The pH optimum is 7.0 and the protein is stable for at least 10 min between pH 6.0-9.0 and for long periods at pH 7.0 It is rapidly inactivated at temperatures greater than 50 degrees C. The enzyme is very sensitive to inhibition by p-chloro-mercuribenzoate, copper and nickel ions.