Luminol chemiluminescence induced by immobilised xanthine oxidase

The calibration for hypoxanthine was linear (r2 = 0.9834, n = 7) up to 17 μM: CL/mV = 0.0371[HX]/μM − 0.0142. The R.S.D. (n = 4) was 1.69% at 8.24 μM and the apparent Km ≥ 16 μM, ≥12× greater for immobilised enzyme than for the soluble xanthine oxidase. The chemiluminescence decreased with increased superoxide dismutase (SOD) concentration (IC50 = 1.2 μg ml−1 and detection limit = 0.25 μg ml−1) and it was shown to decrease to a lesser extent for catalase.