Total Tubulin and Its Aminoacylated and Non‐aminoacylated Forms During the Development of Rat Brain

Abstract

The amount of total tubulin in the soluble fraction of rat brain was measured by a method based on the purification of tubulin previously labeled by incorporation of [14C]tyrosine in the C terminus of its α‐chain. The tubulin content decreased from 2.01 to 1.30 nmol/mg protein when the animals passed from 4 to 30 days of age and then remained practically constant. The amounts of aminoacylated and non‐aminoacylated tubulin present in the soluble brain extracts were determined from the incorporation of [14C]tyrosine into the free acceptor sites of tubulin preparations, that were preincubated without carboxypeptidase A or with this enzyme to eliminate tyrosine and phenylalanine from the C terminus of the α‐chain of tubulin. The values obtained were corrected for the inactivation of tubulin to accept [14C]tyrosine that occurred during the isolation and incubation of the soluble fractions. The ratio non‐aminoacylated/aminoacylated tubulin increased from 1.62 ± 0.03 in the 4‐day‐old rats to 2.11 ± 0.17 in the 120‐day‐old rats. The aminoacylatable tubulin, that is the sum of aminoacylated plus non‐aminoacylated tubulin, decreased from 1.71 to 0.75 nmol/mg protein from 4‐day‐old to 30‐day‐old rats respectively and then remained practically constant. The amount of aminoacylatable tubulin is lower than that of total soluble tubulin. Therefore there is a fraction of tubulin that is unable to accept tyrosine. This non‐aminoacylatable tubulin fraction increases with the age of the animal so that in the 120‐day‐old rats this tubulin species accounts for 48% of the total soluble tubulin. Copyright © 1980, Wiley Blackwell. All rights reserved