Aromatase

Aromatase is an enzyme that converts androgens such as testosterone into estrogens, including estradiol. Its activity links the availability of a precursor substrate to production of a chemically different hormonal signal. The amount of enzyme, available substrate and accumulated product are separate quantities.^[ref]

A 2000 experiment made that distinction useful. Researchers cultured human granulosa-lutein cells, stimulated them with follicle-stimulating hormone, then washed the cells and supplied testosterone for a two-hour challenge. They measured secreted estradiol. Separating the longer stimulation period from the short substrate challenge reduced the confounding effect of progressively depleting testosterone during culture.^[ref]

The experiment illustrates how an enzyme assay can distinguish regulatory induction from immediate catalytic performance. A larger accumulated product amount could otherwise reflect more active enzyme, more available substrate, or a longer reaction time. It is the controlled comparison, not the product measurement alone, that supports an interpretation of altered aromatase activity.