Tyrosine as important contributor to the antioxidant capacity of seminal plasma

A novel post-addition method, based on the trapping of ABTS-radicals, is ap plied for studying the total antioxidant capacity of seminal plasma. A rema rkable profile is observed, in which seminal plasma quenches radicals in a continuous, relatively slow fashion. Five putative antioxidants present in seminal plasma were studied using the same assay. Some of the compounds suc h as ascorbic acid, a-tocopherol and uric acid exert immediate, fast radica l trapping, whereas hypotaurine and tyrosine give rise to the same slow rad ical trapping curve as seminal plasma. Due to this slow, continuous radical trapping, quantification of the total antioxidant capacity (expressed as t rolox equivalent antioxidant capacity, TEAC) strongly depends on the chosen time point after onset of radical trapping. When determined during the slo w antioxidant trapping phase, tyrosine has a powerful antioxidant capacity, which in combination with its relatively high plasma concentration makes i t an important contributor to the total antioxidant capacity of seminal pla sma. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.