In vivo and in vitro complementation between guaB and in vivo complementation between guaA auxotrophs of Salmonella typhimurium.

guaA and guaB mutants of Salmonella typhimurium were isolated utilizing the mutagen, nitrous acid. The guaB mutants were defective for inosine 5'-monophosphate (IMP) dehydrogenase activity and those mutants classified as guaA exhibited no xanthosine 5'-monophosphate aminase activity. In vivo complementation maps were determined for the mutants. The guaB map indicated that at least three complementation regions existed whereas five complementation regions were observed for the guaA mutants. The demonstration of in vitro complementation was also achieved for the guaB mutants by utilizing a process of denaturation and renaturation. All of the guaB mutants that exhibited in vivo complementation were found to exhibit in vitro complementation. No correlation was found between the degree of in vivo complementation exhibited by the various pairs of mutants and the specific enzyme activities of the same mutant pair that yielded in vitro complementation. The kinetic parameters for three of the most active guaB "complemented" enzymes and a renatured wild-type IMP dehydrogenase were then examined. No apparent differences were found in the K(m) values between any of the enzymes for substrate, IMP, activator ion, K(+), and coenzyme, oxidized nicotinamide adenine dinucleotide. Some differences were noted in the apparent V(max) values; the best "complemented" enzyme yielded only 20% of the velocity exhibited by renatured wild-type enzyme.