The activator of cerebroside-sulphatase. A model of the activation

The activator of cereboroside-sulphatase (cerebroside-3-sulphate-3-sulphohydrolase, EC 3.1.6.8) is necessary for the enzymic hydrolysis of sulphatides (cerebroside sulphates) at ionic concentrations in the physiological range. The pH optimum of the reaction is 4.5--4.8. Under similar incubation conditions, a complex is formed between activator and sulphatides which is partially inhibited, due to competitive binding in the presence of cerebrosides of phosphatidylserine. Inhibition depends upon the concentration of the lipids and is of the same order of magnitude as the inhibition (by these lipids) of enzymic sulphatide hydrolysis in the presence of activator. Complex formation between activator and sulphatides is reversible since the complex dissociates partially when certain concentrations of phosphatidylserine are added. Moreover, the rate of sulphatide hydrolysis increases with the concentration of the activator.sulphatide complex in the reaction mixture. This indicates that the activator.sulphatide complex is the substrate for the enzyme and a model for this activation is presented.