Some fluorescent properties of non-enzymic transamination and measurement of the relative molecular mass of protein.

A procedure for transaminating proteins and removing the transaminated N-terminal residue has been used for studying structure-function relationship of protein (Dixon and Fields 1972, Meth. Enzymol. 25, 409-419). We show that it is convenient for measuring the relative molecular masses of proteins by measuring the glycine formed from glyoxylate during such transamination. Quinoxaline derivatives have been synthesized by the reaction of 2-oxo acids from amino acids reacting with o-phenylenediamine. 2-Oxo acids transaminated from amino acids fluoresced at around 405 nm, depending on the nature of residual side groups. The emission maximum of 3-benzyl-2-hydroxy-quinoxaline from the reaction of o-phenylenediamine with phenylpyruvate was at 363 nm. The fluorescent derivatives have been used to study conformational changes of peptides and to detect whether or not N-termini of proteins were blocked.