The enzyme pyrogallol hydroxytransferase uses 1, 2, 3, 5-tetrahydroxybenzene and 1, 2, 3-trihydroxybenzene ( pyrogallol ), whereas its two products are 1, 3, 5-trihydroxybenzene ( phloroglucinol ) and 1, 2, 3, 5-tetrahydroxybenzene.
32.
Phenol oxidase activity is quantified by oxidation of L-3, 4-dihydoxyphenylalanine ( L-DOPA ), pyrogallol ( 1, 2, 3-trihydroxybenzene ), or ABTS ( 2, 2-azino-bis ( 3-ethylbenzothiazoline-6-sulphonic acid ).
33.
The gradual darkening of the ink is due to the oxidation of the iron ions from ferrous ( Fe 2 + ) to ferric ( Fe 3 + ) state by atmospheric oxygen . ( For that reason, the liquid ink had to be stored in a well-stoppered bottle, and often became unusable after a time . ) The ferric ions react with the tannic acid or some derived compound ( possibly gallic acid or pyrogallol ) to form a polymeric organometallic compound.
