On the reaction inactivation of ascorbic acid oxidase

Enzymes of Heavy‐Metal‐Resistant and Non‐Resistant Populations of Silene cucubalus and Their Interaction with Some Heavy Metals in vitro and in vivo

“…Nickel always had an inhibitory effect at higher concentrations than zinc, injuring the enzymes between O.lmM and lmM. Zinc and copper never catised a stimulation of the enzymes tested, as is known for carbonic anhydrase (Randall et al 1973) or for ascorbic acid oxidase (Tokuyama et al 1962). Nickel and cadmium equally did not stimulate, even at low concentrations.…”

Ascorbate Oxidase: A New Method of Purification. Characterization of the Purified Enzyme*

“…The finding that the prosthetic Cu is present in amounts of 8, rather than 6, atoms of Cu per molecule of enzyme is of singular significance. Interest in the catalytic role of the Cu moiety has been heightened by the findings that as high as 85% of the prosthetic Cu is exchangeable, and that the exchange occurs only when the enzyme is in the functional state (Magee and Dawson, 1962); that the so-called "reaction inactivation" of ascorbate oxidase is probably caused by H202 formed by a slow, copper-involved but nonenzymatic secondary reaction (Tokuyama and Dawson, 1962); and most recently, the observation that only 6 of the 8 Cu atoms are enzymatically active (Poillon and Dawson, 1963a,b), Such results not only lend credence to the existence of mixed valency states of the prosthetic Cu but might also indicate specialized roles for each of the two types of Cu, one leading to the formation of H20, the other to H202 as end products of the oxidation. On the other hand, the oxidation of ascorbic acid could involve the transfer of electrons between the two types of Cu with H2Os being formed as an incidental product of the primary reaction.…”

A kinetic study of the suicide inactivation of an enzyme measured through coupling reactions. Application to the suicide inactivation of tyrosinase

“…There is a wide range of enzymes that undergo an inactivation process when acting on a substrate (suicide inactivation), following a branched mechanism consisting of a catalytic route and an enzyme inactivation route that gives rise to a transient phase, until total loss of activity is reached (Ingraham, 1955;Tokuyama & Dawson, 1962;Fernandez-Belda et al, 1982;Frere et al, 1982;Walsh, 1984;Knight & Waley, 1985;Faraci & Pratt, 1985). Kinetic studies of these reaction mechanisms have been carried out under approaches of significant (Waley, 1980(Waley, , 1985Tatsunami et al, 1981) and negligible (Galvez et al, 1981;Tudela et al, 1987a) substrate consumption during the assay time.…”