The Complex Iron-Sulfur Molydoenzyme (CISM) subfamily is the most diverse family of molybdopterin enzymes and the members of this family catalyze a myriad of reactions that are important in microbial life processes. While members of this family can transform multiple substrates, quantitative information about the substrate preference is sparse and the fundamental reasons of substrate selectivity remain unclear. Molybdenum coordination, specifically, the molybdenum coordinating residue has long been proposed to impact the catalytic activity of the enzyme. This presentation discusses the substrate preference and delineate the kinetic underpinning of the differences imposed by protein based ligands to molybdenum using periplasmic nitrate reductase (Nap) as a vehicle.<sup>1</sup> NapA from <i>Campylobacter jejuni</i> has been heterologously overexpressed, and a series of variants, where the molybdenum coordinating cysteine has been replaced with another amino acid, has been produced. The kinetic properties of these variants are discussed and compared with those of the native enzyme, providing quantitative information to understand the role of the molybdenum coordinating residue.

Kinetic control of endogenous ligation to molybdenum in complex iron-sulfur molydoenzyme (CISM) family

ACS Spring 2022

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