Multi-site phosphorylation in ox-kidney branched-chain 2-oxoacid dehydrogenase complex.

Tryptic [32P]phosphopeptides were prepared from [32P]phosphorylated ox-kidney branched-chain complex and analysed by high-voltage paper electrophoresis at pH 1.9. In the maximally phosphorylated complex 3 tryptic [32P]phosphopeptides were identified (TA, TB, TC). RF-values relative to N6-dinitrophenyllysine were (mean +/- SEM for 25 obs.): TA, 1.53 +/- 0.03; TB, 1.07 +/- 0.02; TC, 0.65 +/- 0.01. Relative rates of phosphorylation were TA greater than TB greater than TC. Phosphorylation of TA reached a maximum when about 66% of the complex was inactivated. Phosphorylation of TB and TC was associated mainly with 66-95% inactivation of the complex.