Sonja R. Wyss

Protection of Human Neutrophils by Endogenous Catalase: STUDIES WITH CELLS FROM CATALASE-DEFICIENT INDIVIDUALS

To investigate the importance of catalase as a protecting enzyme against oxidative damage in phagocytic leukocytes, we have tested the functional capacity of neutrophils from two individuals homozygous for Swiss-type acatalasemia and from two individuals heterozygous for this deficiency. In the former cells, 25-30% of residual activity of catalase was present. In the latter cells, the values were close to normal. Chemotaxis towards casein, release of lysosomal enzymes and hydrogen peroxide during phagocytosis of zymosan, and intracellular killing of Staphylococcus aureus were normal in all cells tested. Inhibition of heme enzymes with azide (2 mM) enhanced the respiration and hexose monophosphate shunt activity of normal, but not of homozygous acatalasemic, neutrophils. This indicates that the enhancement in normal cells is, at least in part, due to catalase inhibition. After 15 min preincubation with an H(2)O(2)-generating system (glucose plus glucose oxidase), the respiratory response to zymosan phagocytosis was strongly depressed in the homozygous acatalasemic and in normal, azide-treated neutrophils, but not in normal, untreated cells. Under these conditions, the release of lysosomal enzymes was depressed and that of lactate dehydrogenase enhanced, in catalase-deficient and in catalase-inhibited, but not in normal, neutrophils. During prolonged incubation with the H(2)O(2)-generating system (30-60 min), the reduction level of intracellular glutathione remained high and the hexose monophosphate shunt continued to operate normally in all cells tested. Thus, although the function of neutrophils without catalase activity was depressed by extracellular hydrogen peroxide, the H(2)O(2) degradation via the glutathione redox system remained operative. The results indicate that the glutathione redox system by itself efficiently protects phagocytosing neutrophils against their own oxidative products. During heavy external oxidative stress, however, both catalase and the glutathione redox system are needed for adequate protection.

Properties of erythrocyte catalase from homozygotes and heterozygotes for Swiss-type acatalasemia

The unstable catalase variant found in the blood of individuals homozygous for Swiss-type acatalasemia and the enzyme species present in heterozygous carriers of this rare defect have been further characterized. The mutant enzyme isolated from acatalasemic red cells is considerably more heat labile and differs in electrophoretic mobility from the normal enzyme. Catalase preparations obtained from heterozygotes consist of an apparently uniform enzyme species, probably representing a molecular hybrid, with properties intermediate to those of the normal and the variant enzyme. However, antigenic identity of catalase from all three sources is observed. Model experiments indicate that hybrid catalase molecules can be produced by recombining normal and variant dimer subunits. Fractionation of erythrocytes according to density and age shows that most of the residual catalase activity is localized in juvenile acatalasemic cells, whereas in normal and heterozygous individuals the catalase activity level does not alter significantly during the life span of the red cells. These findings agree with the observation that there is no gene dosage in heterozygotes, their catalase activity values falling within the normal range.

Dissociation of erythrocyte catalase into subunits and their re-association

Zwischen der Tetramer- und der Dimer-Form der Erythrocyten-Katalase besteht ein Gleichgewicht. Dieses lässt sich in vitro durch Variation der Harnstoffkonzentration beliebig verschieben. Das dabei entstehende Dimer zeigt Peroxidase-, nicht aber Katalase-Aktivität. Bei der Reassoziation, deren Geschwindigkeit sich durch andere Proteine beeinflussen lässt, entsteht ein Produkt, das vom nativen Enzym nicht unterscheidbar ist.

HETEROGENEITY OF HUMAN ERYTHROCYTE CATALASE

ABSTRACT. 1. In human erythrocyte catalase three types of heterogeneity are observed: (A) Alternative molecular forms due to conformational changes (B) Partial dissociation of the active tetramer molecule into subunits (C) Genetic variants of the normal enzyme.

Properties of leukocyte catalase from normal and acatalasemic humans

Beim Akatalasie-Fall A.B. ist die in den Leukozyten vorhandene Katalase-Restaktivität wesentlich höher (13%) als diejenige in den Erythrozyten (etwa 1% der Norm), wie dies beim Vorliegen einer instabilen Enzymvariante zu erwarten ist. Die Enzyme beider Zelltypen sind antigen-identisch und zeigen denselben Grad von Thermolabilität.