THE MITOTIC APPARATUS : Physical-Chemical Factors Controlling Stability

Previous investigations have shown that the mitotic apparatus (MA) can be isolated from dividing sea urchin eggs in water buffered at pH 5.6 and that the addition of 1 M hexanediol to the solution raises the usable pH to 6.4. Long chain glycols appeared to be much more effective than related compounds in increasing the stability of the MA, and the aim of the investigations reported here was to determine the basis of this specificity. These experiments show that this impression of specificity is misleading and that under suitable experimental conditions a variety of compounds can be substituted for the glycols. A number of alcohols will duplicate the action of the glycols in stabilizing the MA at pH 6.4, but they must be used at a similar per cent concentration rather than at a similar molar concentration. Increases in the concentration of alcohol or glycol allow isolation at more alkaline pH values, and a pH-concentration relation for the stability of the MA, covering the range from pH 5.6–8, has been determined. These results indicate that the action of these compounds in stabilizing the mitotic apparatus is non-specific and is similar to their effects on the solubility of proteins. The isolation and stabilization of the mitotic apparatus can thus be viewed as a function of the solubility properties of its constituent proteins, opening a variety of new experimental approaches to this problem.