INTERACTION BETWEEN PTERIDINES AND TRYPTOPHAN

Abstract

[longdash]Absorption spectra were studied by means of a Beckman DK1 recording spectrophotometer. Upon complexing, the absorption peak of pteridines in phosphate buffer (pH 7.0), 350-390 m[mu], shifts to a longer wave-length region, approximately 400~430 [mu]/x. In this region, pteridine has a considerable absorption, and even tryptophan in high concentration shows appreciable absorption. The measured extinction was therefore corrected by subtracting the extinction of pteridine and that of tryptophan or serotonin. The molar extinction coefficient of tryptophan was negligibly small compared to that of pteridine in the wave-length region used here. The total concentration of tryptophan (2.5 x 10-3-6.25 x 10-2 [image]) was much larger than that of pteridine (10-4[image]), in the formation of the complex P + Tp? C. In the pteridines, with one exception, the 2 lines for tryptophan and serotonin have the same intercept on the abscissa. This is not true for acridine. This means that the pteridine complexes have the same extinction cooefficient for both tryptophan and serotonin, but acridine does not. A further difference is that the spectral shift was smaller in acridine than in the pteridines. Solutions of bovine serum albumin, a protein containing tryptophan, also were observed to complex with pteridines. It should be noted that the fluorescence of the pteridine complexes was noticeably smaller than that of pteridines themselves.