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AI Tauber, J Wright, FK Higson, SA Edelman and DJ Waxman
NADH-cytochrome b5 reductase is the predominant NADH-diaphorase found in
the human neutrophil (Blood 62:152, 1983). Although this reductase
segregates with the light membranes of nitrogen-cavitated neutrophils
separated on Percoll gradients (which include the plasma membrane markers
alkaline phosphatase and NADPH-oxidase), it is approximately 95% excluded
from plasma membrane-enriched phagocytic vacuoles. The reductase
constitutes approximately 5% of the light membrane fraction
FAD-flavoprotein (14.8 +/- 5.5 pmol/mg protein) and was found in equimolar
concentration with a high potential b cytochrome also present in this light
membrane fraction and tentatively identified as cytochrome b5. Isolation of
the reductase from human neutrophils was accomplished by Triton X-114
solubilization of the light Percoll gradient membranes, followed by
temperature-dependent phase separation and then affinity chromatography on
AMP-Sepharose. The active preparation contained 1.3 mol FAD/mol protein,
migrated on sodium dodecyl sulfate-polyacrylamide gels as a single band
corresponding to an apparent mol wt of 45,000 daltons, exhibited a pl of
5.7 on chromatofocusing and was obtained in greater than 70% yield, with an
overall purification of almost 900-fold. The purified enzyme was
characterized by a high specificity for NADH as electron donor (Km = 6.4
mumol/L v Km greater than 1.6 mmol/L for NADPH) and exhibited a maximal
turnover of ca. 30,000 min-1 at 22 degrees C with either ferricyanide or
cytochrome b5 (Km = 10 nmol/L) as electron acceptor. Although the physical
characterization and biochemical properties described here demonstrate that
this neutrophil NADH b5 reductase is similar to the corresponding liver and
erythrocyte enzymes, its unique function in the neutrophil has yet to be
determined.
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