Type II phosphoinositide 5-phosphatases have unique sensitivities towards fatty acid composition and head group phosphorylation

The catalytic properties of the type II phosphoinositide 5-phosphatases of Lowe's oculocerebrorenal syndrome, INPP5B, Synaptojanin1, Synaptojanin2 and SKIP were analysed with respect to their substrate specificity and enzymological properties. Our data reveal that all phosphatases have unique substrate specificities as judged by their corresponding KM and VMax values. They also possessed an exclusive sensitivity towards fatty acid composition, head group phosphorylation and micellar presentation. Thus, the biological function of these enzymes will not just be determined by their corresponding regulatory domains, but will be distinctly influenced by their catalytic properties as well. This suggests that the Phosphatase domains fulfil a unique catalytic function that cannot be fully compensated by other phosphatases.