Pteridine-binding alpha 1-acid glycoprotein from blood of patients with neoplastic diseases

A glycoprotein was selectively enriched in the supernatant (Fraction b) obtained by alcohol and trichloroacetic acid fractionation of digitonin extracts from blood of patients with neoplastic diseases and of control subjects. Subsequent chromatography with concanavalin A:Sepharose separated a concanavalin A-reactive fraction from a concanavalin A-nonreactive one. In sodium dodecyl sulfate gel electrophoresis, the fractions from both malignant origin as well as control subjects appeared as single bands showing the same mobility. They were identical with the band obtained from commercial alpha 1-acid glycoprotein. In Fraction b of malignant origin, greatly increased amounts of the alpha 1-acid glycoprotein from malignant cases (AGPM) were found as compared to alpha 1-acid glycoprotein from controls (AGPC). Furthermore, AGPC had a higher glycine content than did AGPM. The electrofocusing pattern of AGPM showed additional bands between pH 3.7 and 4.4, whereas AGPC and commercial alpha 1-acid glycoprotein focused between pH 3.2 and 3.8. In contrast to AGPC and to a commercial alpha 1-acid glycoprotein, AGPM is characterized by a chromophoric group with maximal absorbance at 400 nm. It could be detached by treatment with 6 M guanidine hydrochloride thus indicating a noncovalent binding. The spectral data on the separated chromophore at pH 0.5 agreed with that of a 6,7-substituted pteridine. After detachment with reducing agents, a pteridine in its 7,8-dihydro form was indicated by spectral analysis.