Zinc transfer kinetics of metallothioneins and their fragments with apo-carbonic anhydrase

The zinc transfer reactions from Zn-7-MT-I, Zn-7-MT-II, Zn-4 alpha fragment (MT-I) and Zn-4-alpha fragment (MT-II) to ape-carbonic anhydrase have been studied. In each reaction, no more than one zinc ion per molecule is invol ved in metal transfer. Zn-7-MT-I and Zn-7-MT-II donate zinc to apo-carbonic anhydrase and de novo constitute it at a comparable efficiency, while Zn-7 -MT-II exhibits a little faster rate. Surprisingly, Zinc is released from Z n-4-alpha fragment (MT-II) with a much faster rate than from Zn-4-alpha fra gment (MT-I), whose rate is close to that of Zn-7-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 Zn-7-MT-II i n the presence of reduced glutathione shows little difference compare to th e 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 contrib ute to zinc release from metallothioneins.