Binding of kynurenine to catecholamine

Papiliochrome II is a pale yellow pigment of butterflies and consists of one molecule each ofL-kynurenine and N-β-alanyldopamine (NBAD). The aromatic amino nitrogen of kynurenine is bonded to theβ-carbon of NBAD. There are isomers IIa and IIb which show opposite circular dichroism. Theβ-alanine contents of IIa and IIb were determined and the molar ratio of IIa to IIb has proved to be 1.17. The IIa and IIb were decomposed toL-kynurenine and N-β-alanylnorepinephrine (NBANE) by being heated in water at 80°C for 30 min. In both IIa and IIb, circular dichroism of the NBANE showed the same positive peak at 280 nm. The NBANE were further decomposed toβ-alanine and norepinephrine (NE) by being heated in 1 N HC1 at 100°C for 2 hr. The NE was submitted to enantioseparation and has proved to be a racemic mixture in both cases of IIa and IIb. These results are discussed in the light of the enzymic synthesis of IIa and IIb.