Opal suppressor phosphoseryl-tRNA is not a substrate of phosphoserine aminotransferase

A proposal of the role of animal opal suppressor phosphoseryl (Ps)-tRNA is that Ps-tRNA plays a role as an intermediate in the metabolic pathway from 3-phosphoglycerate to glycine. The labeled [32P]phospho[3H]seryl-tRNA was prepared and used as a substrate in the reaction of bovine brain Ps aminotransferase (EC 2.6.1.52) in the presence of alpha-ketoglutarate. By analysis of the reaction product, no amount of 3-phosphohydroxypyruvate was found, even though phosphohydroxypyruvate was noted in the control experiment by use of Ps and alpha-ketoglutarate. These results showed that Ps-tRNA was not a substrate of Ps aminotransferase.