Figure 19.2.

Characteristic HPLC-EC chromatographic profile of nitrohydroxytryptophan. The amino acids tyrosine (Y), 3-nitrotyrosine (Y_3N), tryptophan (W), and 4-and 5-nitrotryptophan (W_4N and W_5N) were used as calibration standards (trace A). The elution profile resulting from the amino acid analysis of the SCOT carboxy-terminal fragment shows the absence of nitrotyrosine and nitrotryptophan and the presence of a peak identified as nitrohydroxytryptophan (W_OH,N) with a retention time of 21 min (trace B). The elution profile obtained after mixing 5-hydroxytryptophan (W_5OH, retention time of 5 min) shows an intense peak corresponding to nitrohydroxytryptophan (W_5OH,N) with an identical retention time to the residue observed in the carboxy-terminal portion of SCOT in vivo (trace C). The electrochemical signal intensities represented by the vertical bars are 1000 nA outside and 50 nA inside the dotted box.