F o n se c a R ib e ir o F. A. Cardoso g r a p h ic s o n th e t e x t In a previous paper ( F o n s e c a R ib e ir o & Ca r d o s o , 1950) in which, we demonstrated the anti-oxidative action of the oxalic acid in relation to adrenalin, we also suggesled the possibility that the addition of oxalic acid to solutions of iron or copper acted by m aking the ionization of the salts of these metals difficult. For this reason there was presented a hypothesis that oxidative processes, catalyzed by

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... ions of iron or copper, should be inhibited or delayed by oxalic acid. In fact, we verified in the above mentioned paper that the ad dition of oxalic acid to the solution of ascorbic acid makes them more stable. In consequence, it should be reasonable to adm it that oxalic acid acting by the form ation of a weak dissociable combination with copper or iron present in the oxidative system could also act in those processes, due to enzymes having an active group form ed by copper or iron. To verify this hypothesis experim entally we decided to study the action of oxalic acid in the oxidative process due to the ascorbic acid oxidase for this enzyme belongs to those having copper in their active group. A supporting reason for the choice of this m aterial for our study was the possibility of finding an explanation to the well known fact of the ex istence in anim al or vegetable m aterials of substances, not yet identified, which protect ascorbic acid against the oxidation by the ascorbic acid oxidase (B a r r o n , B arr o n & K l e m p e r e r , 1936 and P im e n t a , 1941). Indeed, the experim ents we undertook confirm ed the suggested hypothesis of the existence of a definite protective action of oxalic acid in relation to ascorbic * P re se n te d to th e 1st. In ter n a tio n a l C on gress of B io ch em istry , C am bridge, 1949.