Observations on the mechanism of a tanning reaction in Periplaneta and Blatta

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Abstract
Certain aspects of the formation of the sclerotin walls of the oothecae of the cockroaches Blatta and Periplaneta are considered. The walls undergo a process of natural tanning, as a result of which their constituent substance, at first soft and colourless proteinaceous material, is changed into a hard and inert sclerotin. The tanning agent is thought to be an ortho-quinone derived from protocatechuic acid. The material of which an ootheca is composed is largely derived from the secretions of the two colleterial glands. A method of analysis involving paper partition chromatography and absorption spectroscopy is described, by means of which it has been possible to determine the substances present in the glands and to elucidate the changes that occur when their secretions interact. It has been found that the left colleterial gland secretes the structural protein, a polyphenol oxidase and the $4-O-\beta $-glucoside of protocatechuic acid, while the right gland secretes a $\beta $-glucosidase. When mixed in nature or under experimental conditions, the secretions interact and the $\beta $-glucosidase liberates protocatechuic acid from its $\beta $-glucoside. The resulting acid is then oxidized in the presence of the oxidase to a quinone which is believed to form cross-linkages between adjacent molecules of the structural protein giving the tanned product, sclerotin. In the light of this explanation of the sclerotization of the oothecal wall, earlier histochemical results are re-examined. This is thought to be the first report of the isolation of a $\beta $-glucoside of protocatechuic acid from natural sources and of its participation in biological processes.