title: Calcium-independent, pH-regulated effects of S-100 proteins on assembly-disassembly of brain microtubule protein in vitro.
abstract: At alkaline pH, Ca2+ is no longer required for S-100 proteins to inhibit the assembly and to promote the disassembly of brain microtubules in vitro, though the presence of Ca2+ significantly favors the S-100 effects. These effects are inversely related to the microtubule protein concentration and directly related to the S-100 concentration and the pH. Ca2+-independent, pH-regulated inhibition of assembly of phosphocellulose-purified tubulin by S-100 is also described. The microtubule disassembling effect of S-100 is additive to that of alkali (used to raise the pH), and S-100 further disassembles microtubules after alkalinization. Thus the larger inhibitory effect of S-100 on microtubule assembly at alkaline versus acid pH depends on both a decrease in the assembly rate and an increase in the disassembly rate. Together with previous data on this topic, the present findings indicate that S-100 proteins act on microtubule protein in vitro primarily by binding to tubulin, this event being Ca2+-regulated at a given pH, and pH-regulated at a given free Ca2+ concentration.
authors.affiliation: Institute of Anatomy, Medical School, Perugia, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Donato
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008868:Microtubule Proteins / Q000378:metabolism*; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D009418:S100 Proteins / Q000502:physiology*; D014404:Tubulin / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D008868:Microtubule Proteins; D009418:S100 Proteins; D014404:Tubulin; D002118:Calcium