Abstract:

The microtubule protein concentration of the soluble fraction of chick muscles decreases, depending on the assay procedure used, between 25 and 80% during the 11th to the 19th day of embryonic development, dropping much more drastically thereafter. In contrast, a significant increase is observed upon in vitro differentiation of muscle cultures. The specific activity of colchicine binding (once corrected for the actual tubulin content of the microtubular fractions) is 2- to 3-fold higher in the 11-day embryos than in the other ages explored. The colchicine binding decay also shows variations with the age of the muscles or cultures. The protein kinase and diglyceride kinase activities present in the microtubular fractions decrease with development, on a wet weight of tissue basis, but are nearly constant - or even increase - if expressed in terms of the actual tubulin present. Moreover, the variations of these enzymatic activities are not parallel during development. Phosphorylation in vitro, under saturating conditions, of the embryonic and of the undifferentiated muscle microtubular fractions is significantly higher than that of the adult or differentiated microtubules, respectively. This larger phosphate incorporation occurs both in the protein and in the lipidic components of the microtubular fractions. The results obtained are discussed in connection with the possible relationship existing between the enzymatic activities and the probable role of phosphorylation in microtubular function.