New formamidase having substrate specificity for o-formylaminoacetophenone in pig liver

The supernatant (13 000 x g, 20 min) of pig liver homogenate was filtered with Sephadex G-200 and formamidase (aryl-formylamine amidohydrolase, EC 3.5.1.9)activity in each fraction was measured. When formylkynurenine was used as substrate, two peaks of formamidase activity were observed but, with formylaminoacetophenone as substrate, only one peak was observed. Formamidase in the lower molecular weight fraction is known as kynurenine formamidase (FA I), formamidase found here in the higher molecular weight fraction has not been previously reported. This form, designated FA II has been purified about 160-fold from pig liver. The formamidase obtained has substrate specificity for o-formylaminoacetophenone only and could not hydrolyze formylkynurenine. The optimal pH was 8.5 and the Km for o-formylaminoacetophenone was 1.66-10(-3) M. This formamidase was considered to be a new enzyme and was different from FA I in molecular weight and substrate specificity. This new formamidase was present in pig, rabbit and guinea pig liver and not present in rat or mouse liver.