Abstract
This assay for lactose synthase (galactosyltransferase, EC 2.4.1.22) in serum involves two sequential incubations: serially diluted standard or sample antigen is reacted with a fixed amount of antibody; unbound antibody is then adsorbed to wells of antigen-coated microtiter plates and determined by a second antibody directed against the first antibody and coupled to phosphatase. The standard curve is linear for galactosyltransferase concentrations of 10 to 600 micrograms/L. The within-assay CV of a serum sample was 9.3% (SD 4.1%), the between-assay was 3.8% (SD 2.4%). Serum galactosyltransferase concentrations computed from three different dilutions yielded CVs of 6.5% (SD 5.7%, n = 14). We evaluated the method's accuracy by recovery analysis and by comparing enzyme activity in serum with that of purified galactosyltransferase from human milk. The normal reference interval, as estimated from data on 27 healthy blood donors, was 60-436 micrograms/L (mean 224, SD 101 micrograms/L). We applied the assay to samples of serum from ovarian carcinoma patients grouped according to tumor burden. We also determined galactosyltransferase in ascites fluid and found these values useful for diagnosis, whereas determinations in serum may serve mainly for patient monitoring.
Crystal structures of guinea-pig, goat and bovine α-lactalbumin highlight the enhanced conformational flexibility of regions that are significant for its action in lactose synthase
