Human leukocyte peroxidase: activity of a soluble and membrane-bound enzyme form in normal persons and patients with neuronal ceroid-lipofuscinosis.

Human leukocytes contain a peroxidase fraction soluble in 0.1 M phosphate buffer and an insoluble peroxidase component with 10--15 times higher specific activity which can be extracted by 0.1 M phosphate buffer + 0.2% Triton X-100 + 0.2% sodium taurocholate and sonication. Both enzyme components have been estimated spectrophotometrically with the substrate hydrogen peroxide (final concentration 1 mM) and the hydrogen donor p-phenylenediamine (final concentration 28-55 mM) within the first 60 sec. The pH-optimum of the soluble and membrane-bound leukocyte peroxidase is at pH 7.0 with a second smaller peak at pH 5.5. Using 0.2 M boric acid/0.05 M sodium borate buffer (pH 7.6) instead of phosphate buffer a 40%-50% increase of enzyme activity can be achieved. In two patients with the juvenile form of neuronal ceroid-lipofuscinosis (type Spielmeyer-Vogt) the activity of soluble leukocyte peroxidase was considerably reduced, in one patient with the late infantile form (type Jansky-Bielschowsky) the activity was just below the normal range, and in two patients with the adult form (type Kuf) activity was normal. In all patients the activity of membrane-bound leukocyte peroxidase was not significantly altered. Only one of four heterozygotes for the juvenile type had deficient values of the soluble enzyme. The variability of the peroxidase findings in patients and carriers with neuronal ceroid-lipofuscinosis make it uncertain whether this represents the primary enzymic defect.