Reversibly catalyzes the decarboxylation of 3,4-dihydroxybenzoate to catechol. Inactive toward 4-hydroxybenzoate and other benzoate derivatives. 3,4-dihydroxybenzoate + H(+) = catechol + CO2 Inhibited by oxygen. Completely inhibited by HgCl(2). Partially inhibited by ZnSO(4), 2,3,4-trihydroxybeonzoate and 3,4,5-trihydroxybeonzoate. Unaffected by KCl, MnCl(2) or EDTA. Not stimulated by thiamine phosphate, pyridoxal 5'-phosphate or biotin. Not inhibited by hydroxylamine, NaBH(4) or avidin. Optimum pH is 7.0. Stable between pH 6.5 and 9.5. Optimum temperature is 50 degrees Celsius. Stable between 11 and 50 degrees Celsius. At 55 degrees Celsius the half life is 1.5 hours. Homopentamer.