We determined selenium concentrations and activities of the selenoenzyme, glutathione peroxidase (EC 1.11.1.9), in the plasma and erythrocytes of 38 apparently healthy women. We determined selenium concentrations directly by polarized Zeeman-effect flameless atomic absorption spectroscopy. Within-run precision studies for the assays gave CVs of 5.6% for a mean erythrocyte selenium concentration of 149.9 (SD 8.3) microgram/L (n = 10) and 6.4% for a mean plasma selenium concentration of 97.3 (SD 6.2) microgram/L (n = 12). For the women, mean selenium concentrations were 141.4 (SD 14.3) microgram/L of erythrocytes [0.49 (SD 0.07) microgram/g of hemoglobin and 96.3 (SD 14.2) microgram/L of plasma. Glutathione peroxidase activities were measured by a modification of the method of Paglia and Valentine (J. Lab. Clin. Med. 70: 158--169, 1967). Within-run precision studies for the glutathione peroxidase assays gave CVs of 12.8% for mean erythrocyte glutathione peroxidase activity of 77.2 (SD 9.9) U/g of hemoglobin (n = 13), and 8.1% for mean plasma activity of 312.5 (SD 25.2) U/L (n = 11). Mean enzyme activity was 78.7 (SD 12.9) U/g of hemoglobin for erythrocytes and 424 (SD 40) U/L for plasma. Erythrocyte selenium concentrations and glutathione peroxidase activities were positively, but poorly, correlated (r = 0.41, p less than 0.01).

The oxidation products of selenomethionine (SeMet) have been studied via experimental (77)Se NMR and theoretical (77)Se chemical shifts. Four signals are observed: a diastereomeric pair of selenoxides at 840 ppm and two unidentified resonances at 703 and 716 ppm. Theoretical DeltaG and chemical shifts suggest the 703 and 716 ppm resonances correspond to hypervalent selenium heterocycles, called selenuranes, formed by reaction with the amine or acid group of the amino acid and the selenoxide. To identify which of these selenuranes is formed, the amine and acid groups were individually protected. The N-formyl SeMet formed only the selenoxide pair at 840 ppm. The oxidized SeMet methyl ester produced signals at 703 and 716 ppm which are assigned as the Se-N selenurane.

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