Zinc Transfer Kinetics of Metallothioneins and Their Fragments with Apo‐carbonic Anhydrase

The zinc transfer reactions from Zn₇‐MT‐I, Zn₇‐MT‐II, Zn₄‐α fragment (MT‐I) and Zn₄,‐α fragment (MT‐II) to apo‐carbonic anhydrase have been studied. In each reaction, no more than one zinc ion per molecule is involved in metal transfer. Zn₇‐MT‐I and Zn₇‐MT‐II donate zinc to apo‐carbonic anhydrase and de novo constitute it at a comparable efficiency, while Zn₇‐MT‐II exhibits a little faster rate. Surprisingly, Zinc is released from Zn₄‐α fragment (MT‐II) with a much faster rate than from Zn₄‐α fragment (MT‐I), whose rate is close to that of Zn₇‐MT‐I. The reason for the difference is still unknown. Introducing complex compounds into this system may give rise to an effect on the reaction. The transfer from Zn₇‐MT‐II in the presence of reduced glutathione shows little difference compare to the control, suggesting that the reduced glutathione is not involved in zinc transfer process. However, glutathione disulfide does accelerate this zinc transfer reaction remarkably, indicating that the oxidative factors contribute to zinc release from metallothioneins.