Studies on Lipoamide Dehydrogenase of Bakers' Yeast

VII. On the Sulfhydryl Groups of the Enzyme

抄録

Lipoamide dehydrogenase [EC 1. 6. 4. 3] from Saccharomyces oviformis contains 4 moles of free -SH groups per molecule which react with PCMB. The enzyme also contains two catalytic disulfide linkages. Of the 4-SH groups, three react rapidly with PCMB while one reacts slowly. In the presence of 0.5% dodecylsulfate, 6-SH groups per molecule were reacted. This indicates the presence of -SH groups which are not reactive in the absence of the detergent.
When the 3PCMB-sensitive -SH groups were blocked by PCMB, both the lipoamide and the menadione reductase activities were inhibited. After 4-SH groups had reacted with PCMB, however, the menadione reductase activity was restored almost to the level of the native enzyme but the lipoamide reductase activity was not. When the catalytic disulfide as well as the free -SH groups were blocked by PCMB, the lipoamide reductase activity was almost completely inhibited but the menadione reductase activity was slightly increased.
The author wishes to thank Dr. G. Sunagawa, the Director of these Laboratories, for his encouragement and Dr. K. Nakanishi for his valuable advice and discussion.