Figure 6
From: Regulation of homocysteine metabolism by Mycobacterium tuberculosis S-adenosylhomocysteine hydrolase
Effect of phosphorylation on enzyme activity of Mtb-SahH.
(A) Effect of phosphorylation on SAH-hydrolytic activity. Michaelis-Menten plot of SahH-P and SahH-UP is shown with concentration of NAD+ at horizontal axis. Phosphorylation of SahH is accompanied by increase in Km and no change in Vmax (see also Table 2). (B) Effect of phosphorylation on SAH-synthetic activity. Autoradiograph of TLC is shown with reactions containing 4 μM each of SahH-P, SahH-UP and no enzyme. Intensity of SAH spot decreases when SahH-P is used as compared to SahH-UP. (C) Histogram showing percent SAH synthesis by SahH-P and SahH-UP as observed in (B). SahH-P is only 50% active in synthesis of SAH. Error bars represent SD of three independent results. *** p value equal to 0.001 as calculated by Student's t-test. (D) Role of Thr219, Thr220 and Thr221 in SAH-hydrolytic activity. Activities of 1.74 μM each of holo SahH-WT (SahH-P) and holo SahH-T219A/T220A/T221A (marked as SahHtri) purified from E. coli were compared. Graph shows increase in OD at 415 nm of SahH-P with time while SahHtri does not show any detectable activity.
