Abstract
Hydrogen sulfide (H&sub2;S) is a ubiquitous gaseous signaling molecule that plays a vital role in numerous cellular functions and has become the focus of many research endeavors, including pharmacotherapeutic manipulation. Among the challenges facing the field is the accurate measurement of biologically active H&sub2;S. We have recently reported that the typically used methylene blue method and its associated results are invalid and do not measure bona fide H&sub2;S. The complexity of analytical H&sub2;S measurement reflects the fact that hydrogen sulfide is a volatile gas and exists in the body in various forms, including a free form, an acid-labile pool, and bound as sulfane sulfur. Here we describe a new protocol to discretely measure specific H&sub2;S pools using the monobromobimane method coupled with RP-HPLC. This new protocol involves selective liberation, trapping, and derivatization of H&sub2;S. Acid-labile H&sub2;S is released by incubating the sample in an acidic solution (pH 2.6) of 100 mM phosphate buffer with 0.1mM diethylenetriaminepentaacetic acid (DTPA), in an enclosed system to contain volatilized H&sub2;S. Volatilized H&sub2;S is then trapped in 100 mM Tris-HCl (pH 9.5, 0.1 mM DTPA) and then reacted with excess monobromobimane. In a separate aliquot, the contribution of the bound sulfane sulfur pool was measured by incubating the sample with 1 mM TCEP (tris(2-carboxyethyl)phosphine hydrochloride), a reducing agent, to reduce disulfide bonds, in 100 mM phosphate buffer (pH 2.6, 0.1 mM DTPA), and H&sub2;S measurement was performed in a manner analogous to the one described above. The acid-labile pool was determined by subtracting the free hydrogen sulfide value from the value obtained by the acid-liberation protocol. The bound sulfane sulfur pool was determined by subtracting the H&sub2;S measurement from the acid-liberation protocol alone compared to that of TCEP plus acidic conditions. In summary, our new method allows very sensitive and accurate measurement of the three primary biological pools of H&sub2;S, including free, acid-labile, and bound sulfane sulfur, in various biological specimens.