Phosphoamino acid analysis.

It is often valuable to identify the phosphorylated residue in a protein. This unit presents a protocol for partial acid hydrolysis of proteins phosphorylated at serine, threonine, or tyrosine, followed by two-dimensional thin-layer electrophoresis of the labeled phosphoamino acid. Phosphothreonine and phosphotyrosine are more stable to hydrolysis in alkali than are RNA and phosphoserine. Therefore, an alternate procedure using mild alkaline hydrolysis of protein samples to enhance the detection of phosphothreonine and phosphotyrosine is also provided.