1
|
Amdahl MB, Sparacino-Watkins CE, Corti P, Gladwin MT, Tejero J. Efficient Reduction of Vertebrate Cytoglobins by the Cytochrome b 5/Cytochrome b 5 Reductase/NADH System. Biochemistry 2017; 56:3993-4004. [PMID: 28671819 DOI: 10.1021/acs.biochem.7b00224] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cytoglobin is a heme-containing protein ubiquitous in mammalian tissues. Unlike the evolutionarily related proteins hemoglobin and myoglobin, cytoglobin shows a six-coordinated heme binding, with the heme iron coordinated by two histidine side chains. Cytoglobin is involved in cytoprotection pathways through yet undefined mechanisms, and it has recently been demonstrated that cytoglobin has redox signaling properties via nitric oxide (NO) and nitrite metabolism. The reduced, ferrous cytoglobin can bind oxygen and will react with NO in a dioxygenation reaction to form nitrate, which dampens NO signaling. When deoxygenated, cytoglobin can bind nitrite and reduce it to NO. This oxidoreductase activity could be catalytic if an effective reduction system exists to regenerate the reduced heme species. The nature of the physiological cytoglobin reducing system is unknown, although it has been proposed that ascorbate and cytochrome b5 could fulfill this role. Here we describe that physiological concentrations of cytochrome b5 and cytochrome b5 reductase can reduce human and fish cytoglobins at rates up to 250-fold higher than those reported for their known physiological substrates, hemoglobin and myoglobin, and up to 100-fold faster than 5 mM ascorbate. These data suggest that the cytochrome b5/cytochrome b5 reductase system is a viable reductant for cytoglobin in vivo, allowing for catalytic oxidoreductase activity.
Collapse
Affiliation(s)
- Matthew B Amdahl
- Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States.,Department of Bioengineering, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
| | - Courtney E Sparacino-Watkins
- Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States.,Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
| | - Paola Corti
- Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
| | - Mark T Gladwin
- Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States.,Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
| | - Jesús Tejero
- Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States.,Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
| |
Collapse
|
2
|
Gan L, von Moltke LL, Trepanier LA, Harmatz JS, Greenblatt DJ, Court MH. Role of NADPH-cytochrome P450 reductase and cytochrome-b5/NADH-b5 reductase in variability of CYP3A activity in human liver microsomes. Drug Metab Dispos 2008; 37:90-6. [PMID: 18838505 DOI: 10.1124/dmd.108.023424] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
NADPH-cytochrome P450 reductase (CPR) and cytochrome-b(5) (b(5)) together with NADH-b(5) reductase (b(5)R) play important roles in cytochrome P450 3A-mediated drug metabolism via electron transfer. However, it is not clear whether variability in expression of these accessory proteins contributes to the known interindividual variability in CYP3A activity. CPR and b(5) were measured in human liver microsomes (HLMs) by spectrophotometry and immunoblotting. HLMs from elderly (>or=46 years) male donors (n=11) averaged 27% (P=0.034) and 41% (P=0.011) lower CPR levels than young (<or=45 years) male donors (n=21) for spectrophotometric and immunoblot values, respectively. Similarly, HLMs from elderly male donors averaged 43% (P=0.034) and 47% (P=0.011) lower b(5) levels than young male donors for spectrophotometric and immunoblot values, respectively. alpha-Lipoic acid and 6-propyl-2-thiouracil were evaluated for selectivity of inhibition of CPR and b(5)R activities, respectively, using recombinant enzymes and HLMs, as well as for effects on CYP3A-mediated triazolam hydroxylation in HLMs with either NADH or beta-NADPH. The results indicate that both compounds are relatively nonselective inhibitors of CPR and b(5)R activities. Finally, we used multivariate regression analysis and showed that variability in CPR or b(5) expression between HLMs does not contribute significantly to variability in CYP3A-mediated midazolam hydroxylation. Consequently, while aging is associated with decreased CPR and b(5) expression in human livers, this effect does not contribute to CYP3A variability.
Collapse
Affiliation(s)
- Lu Gan
- Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, 136 Harrison Avenue, Boston, Massachusetts 02111, USA
| | | | | | | | | | | |
Collapse
|
3
|
Borgese N, Pietrini G, Gaetani S. Concentration of NADH-cytochrome b5 reductase in erythrocytes of normal and methemoglobinemic individuals measured with a quantitative radioimmunoblotting assay. J Clin Invest 1987; 80:1296-302. [PMID: 3680497 PMCID: PMC442383 DOI: 10.1172/jci113205] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The activity of NADH-cytochrome b5 reductase (NADH-methemoglobin reductase) is generally reduced in red cells of patients with recessive hereditary methemoglobinemia. To determine whether this lower activity is due to reduced concentration of an enzyme with normal catalytic properties or to reduced activity of an enzyme present at normal concentration, we measured erythrocyte reductase concentrations with a quantitative radioimmunoblotting method, using affinity-purified polyclonal antibodies against rat liver microsomal reductase as probe. In five patients with the "mild" form of recessive hereditary methemoglobinemia, in which the activity of erythrocyte reductase was 4-13% of controls, concentrations of the enzyme, measured as antigen, were also reduced to 7-20% of the control values. The concentration of membrane-bound reductase antigen, measured in the ghost fraction, was similarly reduced. Thus, in these patients, the reductase deficit is caused mainly by a reduction in NADH-cytochrome b5 reductase concentration, although altered catalytic properties of the enzyme may also contribute to the reduced enzyme activity.
Collapse
Affiliation(s)
- N Borgese
- Consiglio Nazionale delle Ricerche Center of Cytopharmacology, Milan, Italy
| | | | | |
Collapse
|
4
|
Borgese N, Macconi D, Parola L, Pietrini G. Rat erythrocyte NADH-cytochrome b5 reductase. Quantitation and comparison between the membrane-bound and soluble forms using an antibody against the rat liver enzyme. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)33526-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
|