Non-Essential Activation of Rat Liver Porphobilinogen-Deaminase by Folic Acid

This report demonstrates the ability of folic acid to activate rat liver porphobilinogen-deaminase (PBG -D). Lineweaver-Burk analysis revealed an increase in V (38%) without affecting the K . In the concentration range assayed, secondary replots of 1/Δslope and 1/Δintersect versus 1/[folic acid] yielded straight lines, indicating the binding of a single molecule of activator to the enzyme PBG-D , with a K = 1.66 mᴍ. Results presented here show that folic acid acts as a non-essential activator (α = 1; β = 1.6). The activating effect of folic acid has been observed employing the 35-70% ammonium sulphate precipitated fraction, desalted by dialysis or gel filtration, whereas no action was detected when other partially purified PBG -D preparations were utilized as the enzyme source, suggesting either the presence of sites saturated for the activator, or the existence of a different structural protein conformation, or both.