In an attempt to graft the R selectivity of AmISY onto CrISY, we produced a series of CrISY mutants incorporating these sequence changes of AmISY (supplemental Table S2). In the construct CrISY-R1, two mutations, A246W and F342L, increased R-citronellal production from not detectable to 1%. Substitution of two additional residues (I345V and A346V) increased the fraction of R-citronellal 17-fold. Another mutation added to CrISY-R1 (F149W) achieved a 7-fold increase in R product. Either way, the high stereoselectivity of AmISY was not attained. Additional sequence changes, perhaps at second-shell residues, must be required to guarantee selective hydride transfer.