Final answer:
The compound with the highest affinity for its cognate enzyme is a substrate with a low Km value, indicating a strong binding affinity between the enzyme and the substrate.
Step-by-step explanation:
To determine which of the following compounds has the highest affinity for its cognate enzyme, we should look at the nature of their interactions with the enzyme. A substrate with a low Km value is characteristically indicative of a high affinity between the substrate and the enzyme, meaning that even at low concentrations the enzyme actively binds to the substrate. In contrast, a substrate with a high Km value indicates weaker binding affinity. While competitive and non-competitive inhibitors both affect enzyme activity, they do not reflect the natural consonance between an enzyme and its true substrate. Competitive inhibitors mimic the substrate and bind to the active site, whereas non-competitive inhibitors bind to an allosteric site, affecting enzyme function without direct competition at the active site.
Therefore, the compound with the highest affinity for its cognate enzyme is b) A substrate with a low Km value.