Beyond Vmax and Km: How details of enzyme function influence geochemical cycles

Abstract:

Enzymes catalyze the vast majority of chemical reactions relevant to geomicrobiology. Studies of the activities of enzymes in environmental systems often report V_max (the maximum possible rate of reaction; often proportional to the concentration of enzymes in the system) and sometimes K_m (a measure of the affinity between enzymes and their substrates). However, enzyme studies – particularly those related to enzymes involved in organic carbon oxidation – are often limited to only those parameters, and a relatively limited and mixed set of enzymes. Here I will discuss some novel methods to assay and characterize the specific sets of enzymes that may be important to the carbon cycle in aquatic environments. First, kinetic experiments revealed the collective properties of the complex mixtures of extracellular peptidases that occur where microbial communities are diverse. Crystal structures combined with biochemical characterization of specific enzymes can yield more detailed information about key steps in organic carbon transformations. These new techniques have the potential to provide mechanistic grounding to geomicrobiological models.