The term phosphatidylinositol (PtdIns) cycle was coined in the mid 50's of the last century, probably in reminiscence to the detection of major metabolic cycles  detected and named shortly before. Three PI4K isoforms which we called PI4K230, PI4K92 and PI4K55 (according to the molecular weights of the corresponding proteins of 230,92 and 55 kDa) have now been cloned and sequenced. All three PI4K isoforms differ greatly in their N-terminally located regulatory domains. Both PI4Ks (230 and 55) contain structural elements responsible for association with membranes: PI4K230 a pleckstrin homology (PH) domain and PI4K55 a palmitoyl residue. Potential phosphorylation sites in PI4K230 suggest regulatory function of CAMP-dependent protein kinase (PKA), protein kinase-C, caseine kinase I1 and protein tyrosine kinases; PI4K92 has a high potential for regulation by phosphorylation; eight sites have been identified indicating participation of proline directed cyclin-dependent protein kinases, like cdc2, or cyclic monophosphate-dependent protein kinases (PKA/PKG; and ca2 + / calmodulin-dependent protein kinase (CaMKII).

References

1.Heilmeyer LM Jr,et al. IUBMB Life. 2003;55(2):59–65.