Soluble and microsomal forms of NADH-cytochrome b5 reductase from human placenta Similarity with NADH-methemoglobin reductase from human erythrocytes

Membrane-bound cytochrome b5 reductase (methemoglobin reductase) in human erythrocytes. Study in normal and methemoglobinemic subjects.

“…2 1 Isoelectric focusing in a 6-8 pH gradient (21) followed by specific staining for NADH-diaphorase (20 abolished by pretreatment with the antiserum directed against the soluble cytochrome b5 reductase. Under these conditions the soluble enzyme is also completely inhibited (not shown) (8).…”

“…The different preparations were incubated with a chicken antiserum prepared against human erythrocyte-soluble cytochrome b5 reductase (8) in the presence of 5% (vol/vol) of polyethylene glycol. Increasing amounts of antiserum were added to constant amounts (expressed as units of methemoglobin-ferrocyanide reducing activity) of enzyme.…”

“…The enzyme locus (DIA,) has been assigned to chromosome 22 (3,4). It has been demonstrated that this erythrocyte enzyme is Received for publication 14 July 1980 and in revised form 15 September 1980. actually a soluble NADH-cytochrome b5 reductase (5)(6)(7)(8) that reduces a soluble cytochrome b5. The reduced cytochrome b5 interacts directly with methemoglobin (5,9).…”

“…In the other cells, the NADH-cytochrome b5 reductase is predominantly bound to the membranes: endoplasmic reticulum (10) and mitochondria (11). However, a soluble form of the enzyme has also been found in the cytosolic fraction of human placenta (8) and rabbit liver (12).…”

Development and validation of a spectrophotometric assay for measuring the activity of NADH: cytochrome b5 reductase in human tumour cells

“…The enzyme is usually bound to the endoplasmic reticulum, but has also been found bound to outer mitochondrial membranes in the liver (Sottocasa et al, 1967) and plasma membranes in erythrocytes (Choury et al, 1981). In addition, an immunologically related soluble form of the enzyme has been purified from erythrocyte cytosol (Passon et al, 1972;Leroux et al, 1977) and from rabit liver cytosol (Lostanlen et al, 1987). Cytochrome b5 reductase transfers reducing equivalents from NADH to cytochrome b5 in the endoplasmic reticulum, which, in turn, donates electrons to a variety of electron acceptors, which include fatty acid desaturases, elongase, cytochrome P450, methaemoglobin and metmyoglobin (Ghesquier et al, 1985;Guiray and Arinc, 1991).…”