|Budget Amount *help
¥5,300,000 (Direct Cost : ¥5,300,000)
Fiscal Year 1995 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1994 : ¥3,800,000 (Direct Cost : ¥3,800,000)
For construction of artificial enzymes, it is of importance to introduce apoenzyme functions into the catalytic systems. A molecule possessing catalyst and substrate binding sites, and an ability of transition-state stabilization would be an apoprotein model. As a flavin receptor, 2,6-diamidopyridine and melamine derivatives were exploited. These molecules bind a flavin via three hydrogen bonds at the uracyl moiety of an isoalloxazine ring in chloroform. A melamine derivative bearing a guanidinium ion was found to bind strongly 6-azaflavin (oxidation-active flavin) via five hydrogen bond. The binding constant for 6-azaflavin is 140,000 M^<-1> in CHCl_3. By using this receptor, the reactiviy of a flavin was found to be controlled by hydrogen bonding. Namely, the N (1) -hydrogen bonding accelerates the oxidation at the N (5) -position, and the N (5) -hydrogen bonding facilitates the oxidation proceeding via C (4a) -attack.
The melamine derivative bearing a guanidinium ion was found to bind strongly FMN.Water-soluble FMN is extracted by chloroform in the presence of the receptor, whereas not riboflavin. The receptor also acts as an FMN-carrier through a liquid membrane.
This receptor molecule accelerates markedly the rate of the oxdative decarboxylation of pyruvate catalyzed by a thiazolium ion bearing a thymine moiety. In this case, the functional group, guanidinium ion acts as not only pyruvate binding site, but also activates pyruvate due to hydrogen bonding to the carbonyl oxygen.
Since three different functional groups can be easily introduced into the melamine derivatives, the results obtained in the present research project would contribute to design of more sophisticated catalytic systems.