The effect of S‐100a and S‐100b proteins and Zn2+ on the assembly of brain microtubule proteins in vitro

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Abstract
The homologous proteins S‐100a and S‐100b affect the microtubule system in a distinctly different way in the presence of low molar ratios of Zn2+. Assembly of brain microtubule proteins can be almost completely inhibited and rapid disassembly can be induced by low molar amounts of S‐100b in the presence of low molar ratios [2–4] of Zn2+. Higher molar ratios per S‐100b (>4) potentiate the general Zn2+ effect, promoting the formation of sheets of microtubules. However, the effect of S‐100a is quite different, no inhibition of assembly can be observed and the presence of S‐100a seems to protect the microtubule proteins against the effect of Zn2+ by chelating the Zn2+ and decreasing the free metal‐ion concentration. S‐100a or S‐100b cannot bind to the microtubule polymer‐form, either in the absence or in the presence of Zn2+.