Taking a cue from our two previous papers involving surface transplants, one an active surface transplant and the other a whole surface transplant, we decided to attempt an active site transplant involving a mesophile aminopeptidase from Bacillus subtilis, known as TET, and its hyperthermophile homolog from Pyrococcusfuriosus. We showed, through comparisons of the catalytic parameters of the two enzymes and the derived enzyme that (a) we had lost most of the activity, but (b) that the residual activity (more than an order of magnitude lower) actually suggests that the catalytic parameters are an interesting combination of the two ancestors. One aspect in particular which was fascinating was the import of a substrate-induced inhibition at higher substrate concentrations which was present in one ancestor, but not in the other, and which was also observed in the active-site-transplanted enzyme, with the transplant having resulted in the import of the substrate-induced inhibition characteristic.

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