Theoretical study on the relationship between structure and function of ricin A-chain functional region's mutant

According to the experimental results on the influences of biological activ ity due to the point-mutant of ricin A-chain's functional region (Tyr 80, T yr 123, Glu 177, Arg 180), the functional region of RTA and its mutants are studied theoretically by semi-empirical quantum chemical AM1 method, The i ntrinsic reason of the influences on biological activity due to functional region's point-mutant is analyzed theoretically by the change of frontier m olecular orbital's property and energy level. The mutant (Tyr 123-->Trp) wh ich possesses a higher biological activity than RTA is predicted theoretica lly.