Enzymic determination of fructose in seminal plasma by initial rate analysis

We describe a spectrophotometric assay for fructose in seminal plasma. The method is based on reduction of fructose by a commercially available preparation of sorbitol dehydrogenase (EC 1.1.1.14), with the concomitant oxidation of NADH. The initial rate of NADH oxidation, which is proportional to the fructose content of seminal plasma, can be measured either with a recording spectrophotometer or by conventional two-point kinetic assay. The method was as accurate, precise, and sensitive as, and more specific and rapid than, currently used colorimetric (resorcinol) methods for fructose determination. Values (mmol/L) for fructose in seminal plasma from several species are: man, 9 +/- 2 (SD); cynamolgus monkey (Macaca fasicicularis)., 108 +/- 19; bull, 30 +/- 1; and rabbit, 13 +/- 4. These values agree with previously published results. We believe the method is appropriate for both research and clinical use.