Water-insoluble papain conjugates of hydrous titanium(IV) oxide and of surface-coating materials modified to contain hydrous titanium(IV) oxide

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Abstract
Hydrous titanium(IV) oxide, on exposure to a dilute solution of papain (EC 3.4.22.2) at pH 7.0, has been demonstrated to bind the enzyme. The resultant water-insoluble hydrous titanium(IV) oxide–papain conjugate exhibits substantial esterolytic and proteolytic activity, a broad profile of pH versus esterolytic activity, and stable activity during storage in aqueous suspension at 4 °C. The foregoing observations are discussed in the light of the known chemical and physical structures of hydrous titanium(IV) oxide. An investigation has revealed that hydrous titanium(IV) oxide may be included in surfaces of emulsion paint or epoxy-resin and still retain an ability to bind papain. This property of hydrous titanium(IV) oxide forms the basis of a novel procedure for the convenient preparation of surface-coating–enzyme conjugates exhibiting catalytic activity and the properties of conjugates prepared by this procedure were investigated. Papain bound to hydrous titanium(IV) oxide that had been included in emulsion paint was found to possess substantial specific esterolytic activity and to maintain activity during storage, whereas papain bound to hydrous tatanium(IV) oxide that had been included in epoxy-resin was found to possess lower specific esterolytic activity and to be less stable during storage. Such surface-coating–enzyme conjugates, having enzyme attached to a single surface, may be conveniently operated against continuous feeds of substrate solution. Further, since such conjugates are easily withdrawn from substrate solution, catalysis may be terminated rapidly. It has also been demonstrated that unmodified surfaces of glass, epoxy-resin, and emulsion paint form conjugates with papain by adsorption but that such conjugates are unstable to storage in substrate solution.

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