The oxidases and other oxygen - catalysts concerned in biological oxidations / by J. H. Kastle.

  • Joseph Hoeing Kastle
Date:
[1910]
Catalogue details

Licence: In copyright

Credit: The oxidases and other oxygen - catalysts concerned in biological oxidations / by J. H. Kastle. Source: Wellcome Collection.

    86/168 (page 84)
    gen derivatives of the polypeptids were not acted upon. The action of tyrosinase on a polypeptid containing tjn-osin was modified to! some extent by various amino acids. Thus the action was greatlyl accelerated by 1-prolin, whereas it was retarded by aspartic and glutaminic acids. Prolin was found to act especially energetically in augmenting the action of tyrosinase on glycy 1-1-tyros in anhydride. They also found tyrosinase to act on phenol, giving a brown color,] and here again the color produced by the action of tyrosinase was modified by amino acids. Thus glycocoll and phenol gave a cochineal color, and prolin and phenol gave a violet reaction. These authors conclude that the character of the pigment resulting from the action of tyrosinase on tyrosin is dependent upon the combination in which the tyrosin exists. In the free state it is colored differently from what it is when in the anhydride or in the polypeptids. The amino acids when present apparently take part in the production of the pigment. In a later communication (2) these authors point out that tyrosinase acts rapidly on d-alanyl-l-tyrosin, and on 1-leucyl-l- tyrosin. They also found it to act on adrenalin with the rapid pro-I duction of a red color and ultimately dark red flocculi. It was also found to act on the three optical isomers of adrenalin with equal rapidity. ON THE NATURE OF TYROSINASE. Bach and Chodat (28) (see p. 118-120) have shown that laccase isj composed of two distinct substances, an oxygenase—that is, a sub-| stance which forms a peroxide by taking up of oxygen and which! is replaceable by hydrogen peroxide,—and a peroxidase, which] activates this peroxide or the hydrogen peroxide added. According! to this conception, the system, peroxidase + hydro-peroxide, is to all ] intents and purposes identical with the oxidases in its general behav- ] ior toward readily oxidizable substances. The question, therefore, ] naturally suggests itself in this connection, Is tyrosinase similarly 1 constituted? In other words, Is .this oxidase composed of a specific ) peroxidase and an oxygenase, and can other peroxides, such as hydrogen peroxide, take the part of the oxygenase in tyrosinase! oxidations? Bach (21) has attempted to answer these questions. According to this observer, tyrosinase contains a peroxidase and an oxygenase, and it is to the former that it owes its specific power to oxidize tyrosin and similarly constituted substances, since hydrogen peroxide may be employed in the place of the oxygenase contained < in tyrosinase in accomplishing the oxidation of tyrosin. Thus he ob- served that a fresh aqueous extract of young potato tubers rapidly j oxidizes and blackens a solution of tyrosin, whereas if the expressed juice of finely ground new potatoes be allowed to stand for twenty- ]