What is "geranyltranstransferase"

In enzymology, a geranyltranstransferase is an enzyme that catalyzes the chemical reaction

geranyl diphosphate + isopentenyl diphosphate $\rightleftharpoons$ diphosphate + trans,trans-farnesyl diphosphate

Thus, the two substrates of this enzyme are geranyl diphosphate (a 10 carbon precursor) and isopentenyl diphosphate (a 5 carbon precursor) whereas its two products are diphosphate and trans,trans-farnesyl diphosphate (a 15 carbon product).

This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups.