COMPARATIVE STUDIES ON THE TWO FORMS OF YEAST INVERTASE

Abstract

Two active components of the yeast invertase, designated as S-I and S-II, were highly purified and compared with each other with respect to the inhibition and activation characteristics, UV absorption spectrum and thermostability. These 2 enzymes were different in the following points. The S-II enzyme is more sensitive to heavy metal ions, especially to Ag+ and Hg2+, than the S-I; the S-n activity is inhibited significantly by these 2 metal ions in concentrations of 10-6-10-7[image], while no measureable inhibition of the S-I was demonstrated. The S-I and S-II enzymes form stable derivatives of iodine, which retained approximately 40 and 10% of activities of their native forms, respectively. Cysteine activates the S-n enzyme to a larger extent but does not restore the activity of the iodinated S-n, while it reactivates the S-I enzyme. With the S-II enzyme a larger increase in the absorbancy at 294 mu by basification was demonstrated than with the S-I enzyme, and the former is much more heat labile at the alkaline pH ranges than the latter. On the basis of these results the possibility of difference in the molecular configuration between these 2 enzymes was discussed.