the value of the apparent equilibrium binding constant was found to depend on the phosphorylation state of the guanine nucleotide bound to the tubulin exchangeable site ( e-site ) , with ka values of 4.9 x 10 ( 4 ) and 8.19 x 10 ( 4 ) m-1 for gtp- and gdp-tubulin , respectively .
C0018328
guanine
C0018353
gtp