Suppose you develop an in vitro assay to accurately measure the activity of purified TrbL protein. If you carry out site-directed mutagenesis on your cloned wookiee trbL gene, you can express mutant alleles of trbL in E. coli and purify mutant TrbL protein for study. You create two different mutant alleles of trbL: one of these mutations codes for an Ala!Glu change at residue 100 (A100E) and another codes for a Leu!His change at reside 113 (L113H). You purify the two mutant proteins and use them in your TrbL assay. The A100E mutation does not change TrbL activity but the L113H mutation results in a loss of TrbL activity. What can you conclude about the roles of the Ala-100 and Leu- 113 residues in TrbL activity?