What are different forms of enzymes that catalyze the same reaction called?

The term "isoenzymes" refers to different forms of enzymes that catalyze the same biochemical reaction but might differ in their structure, properties, or regulatory mechanisms. These variations can arise due to genetic differences, alternative splicing, or post-translational modifications, allowing the organism to fine-tune enzyme activity under varying physiological conditions.

For instance, in humans, there are multiple isoenzymes for lactate dehydrogenase, which can be found in different tissues and have distinct roles in metabolism. The presence of isoenzymes can provide advantages such as tissue-specific regulation, adaptation to different metabolic needs, and varying sensitivity to inhibitors or activators.

In contrast, the other options refer to different concepts. Activators enhance enzyme activity rather than being different forms of the same enzyme. Coenzymes are non-protein molecules that assist enzymes in catalyzing reactions but are not different forms of the enzymes themselves. Substrates are the specific reactants an enzyme acts upon, not variations of the enzyme. Therefore, isoenzymes is the most accurate term for the question asked.