title: Mechanism of endogenous phosphorylation of microtubule proteins during GTP-induced microtubule assembly and implications for stability of the assembled structures.
abstract: Cycle-purified microtubule protein from mammalian brain incorporated [32P]Pi upon incubation with [gamma-32P]GTP under the conditions used to promote assembly. This phosphorylation also occurred in the same proteins when phosphorylated with [gamma-32P]ATP and was only slightly stimulated by cAMP. GTP was a much less effective substrate than ATP. The transfer of phosphoryl groups from [gamma-32P]GTP to endogenous proteins followed a linear time-course and was stimulated by low concentrations of ATP and, more efficiently, by ADP. These data are in agreement with the predictions derived from a mechanism of phosphorylation by which [gamma-32P]GTP does not act as a phosphoryl donor for the protein kinase activity but, instead, only as a repository of high group transfer potential phosphoryl groups used to make [gamma-32P]ATP, from contaminating ADP, by means of the nucleoside diphosphate kinase activity. Using 100 mM fluoride, which suppressed protein phosphorylation without inhibiting the nucleoside diphosphate kinase activity, formation of [gamma-32P]ATP was detected. Fluoride was also able to protect microtubules from a slow depolymerization which was found to occur during long-term incubation of microtubules. This indicates that the phosphorylation observed in the presence of GTP is sufficient to destabilize microtubules.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002540:Cerebral Cortex / Q000032:analysis*; D005459:Fluorides / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D008868:Microtubule Proteins / Q000378:metabolism*; D008870:Microtubules / Q000187:drug effects / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation
chemical_list: D008868:Microtubule Proteins; D010710:Phosphates; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D005459:Fluorides