Water-insoluble papain conjugates of titanium (IV)-activated supports

Abstract

Glass fibre paper, treated with titanium (IV) chloride and subsequently water-washed, has a significant quantity (27.7 μg/cm 2) of surface-bound titanium (IV) which may be removed by exposure to acidic hydrogen peroxide solution. This observation supports the view that materials that have been treated with titanium (IV) chloride by the method of Emery et al. 1 possess a surface layer of hydrous titanium (IV) oxide which is able to bind protein in a manner analogous to that of free hydrous titanium (IV) oxide. Titanium (IV)-activated derivatives of polypropylene netting, zirconia fibre sheet and glass fibre paper have each been found able to bind papain. The papain conjugate of each titanium (IV)-activated support exhibited a high ratio of specific proteolytic activity to specific esterolytic activity. These ratios ranged from 29 to 64% of the ratio for the soluble papain employed; the highest ratio obtained was for the papain conjugate of the titanium (IV)-activated glass fibre support. This conjugate was also very satisfactory with regard to its protein content, specific activities, catalytic stability, pH range of activity, mechanical stability and ease of separation from substrate solution. The papain conjugate of titanium (IV)-activated polypropylene was more active and more stable than a papain conjugate of non-activated polypropylene. However, both preparations lost their activity during prolonged storage in substrate solutions, even though the activity of the papain conjugate of titanium (IV)-activated polypropylene was initially maintained for about 20 days. In each case the loss of activity is attributed to protein desorption during storage. The papain conjugate of titanium (IV)-activated zirconia was catalytically stable to storage in substrate solutions but suffered from poor wet strength.