Fig. 2.

Activation of hMS in the presence of hMSR. Purified MS (2.3 μg), whose specific activity was 2.2 μmol·min⁻¹·mg⁻¹ protein as measured by using the aqCbl/DTT reducing system, and the indicated amount of purified MSR were used for each reaction. MS activity was measured under aerobic conditions as described in Materials and Methods, with DTT present to allow nonenzymatic reduction of aqCbl to cob(II)alamin. The reactions were initiated by addition of AdoMet after a 3-min preincubation and quenched after 1 min. Shown is Met formation as a function of MSR concentration. (Inset) The stoichiometry of the reaction.