An enzyme system of banana fruit (Musa sapientum) was capable of catalysing the hydroxylation of the monophenol, tyramine, to the diphenol, dopamine (3,4-dihydroxyphenylethylamine). Unlike some tyrosinases, the reaction not stimulated by catalytic amounts of diphenolic reaction product. Ascorbic acid, however, reduced the initial lag period in the oxidation of tyramine, stimulated the reaction rate and promoted the accumulation of dopamine during the first few minutes of the reaction. The hydroxylation of tyramine was apparently dependent upon molecular oxygen. On the basis of these observations it is tentatively suggested that the enzyme is a tyramine hydroxylase which may be responsible for the formation of dopamine in the banana.

Article Enzymes of the banana plant: Optimum conditions for extraction