A Comparison of Certain Oxidising Enzymes of the Higher and Lower Plants.

PEROXIDASE, the enzyme which induces the oxidation of guaiacum and other oxidisable substances by hydrogen peroxide, is known to be present in nearly all living plant cells. Many plants, moreover, are able to cause the blueing of guaiacum without the addition of hydrogen peroxide; these have been considered to contain a direct oxidase, phenolase or laccase. Bach and Chodat consider such an enzyme system to be composed of oxygenase in addition to peroxidase, oxygenase being described as an enzyme-like substance, which can. unite with the oxygen of the air to form a peroxide, the system being analogous to that formed by hydrogen peroxide and peroxidase [Chodat, 1910]. The two components, oxygenase and peroxidase, have been separated to a certain extent by fractional precipitation with alcohol [Bach and Chodat, 1903], by dialysis, and by ultra filtration [Bach, 1916]. Most of the work of Bach and Chodat on oxidases has been carried out on the basidiomycetes, but oxygenase has been mentioned in connection with various phanerogams, e.g. Rhus vernicifera, the potato, the apple [Chodat, 1910], wheat and the sunflower [Bach and Oparin, 1923]. Onslow, M. W. [1920] has postulated that, for the higher plants, three components are present in what has been termed an oxidase or laccase, namely: an aromatic substance with two hydroxyl groups in the ortho-position, or "catechol" substance, from which a peroxide can be formed, and two enzymes; an oxygenase which catalyses the formation of peroxide from the "catechol" substance, and a peroxidase, which decomposes the peroxide with the production of active oxygen. The catechol substance is soluble in alcohol, therefore when an enzyme preparation is made by the usual method of alcoholic precipitation, it does not cause the direct blueing of guaiacum unless a substance containing the ortho-dihydroxy grouping (catechol, protocatechuic acid or aldehyde, caffeic acid, etc.) is added. The action of the oxygenase is apparent in the rapid darkening of the orthodihydroxy substance. It is, moreover, postulated that the discoloration on injury of plants containing a direct oxidase system is due to the action of the oxygenase on the catechol compound.