And finally PIPKs of type III are PtdIns3P 5-kinases that phosphorylate PtdIns to PtdIns(3,5)P2, which prototype is Fab1 in yeast (see  for descriptive picture). The substrate specificity of type I and II depends on the so-called activation loop. The activation loop is a segment of 22 to 27 amino acid residues, located close to the C-terminal end of the catalytic domain in all PIPKs.
This leads to PIPKs of type III being PtdIns3P 5-kinases that convert PtdIns into PtdIns(3,5)P2, exemplified by Fab1 in yeast (see  for a detailed illustration). The substrate specificity of type I and II is influenced by the activation loop. The activation loop is a segment of 22 to 27 amino acid residues, located near the C-terminal end of the catalytic domain in all PIPKs.