Characterization of an isoxanthopterin binding protein from Oncopeltus fasciatus.

Oncopeltus embryos contain a relatively large amount of isoxanthopterin, a small part of which is tightly bound to a high molecular weight (～500,000) protein. This causes a characteristic shift in the excitation and fluorescence maxima of isoxanthopterin from 348–409 nm to 355–420 nm, which provides a ready assay for the complex. Partial purification of the complex has been achieved, and some of its properties are described.