Fig 4.

Enzymatic confirmation of the absence of IMPDH activity in ΔguaB mutant lysates. Enzymatic activity was measured for whole-cell lysates from wild-type strain G27 (A) and the ΔguaB deletion mutant (B). Optical density measurements at 290 nm were taken every 30 s for 2 h and used as a measure of XMP production. Enzymatic activity being substrate (IMP) and NAD dependent was shown by conducting the assays in the absence of either IMP or NAD. Lysates were generated twice, assays were each conducted twice, and linear regression lines were calculated for each assay. R² values for linear regression lines for WT and ΔguaB strains (under NAD addition and IMP addition conditions) were 0.996 and 0.675, respectively, and 1/slope values were 733.8 and 315,600, respectively.