High impact information on CYB561

• We have purified cytochrome b561 from bovine adrenal chromaffin granules by reverse phase chromatography and have determined internal amino acid sequences from peptides [1].
• Cytochrome b561 is a transmembrane electron transport protein that is specific to a subset of secretory vesicles containing catecholamines and amidated peptides [1].
• RNA blotting experiments indicate that cytochrome b561 is expressed in the adrenal medulla and all brain regions of the cow, but not in visceral organs [1].
• The structure of cytochrome b561, a secretory vesicle-specific electron transport protein [1].
• Subsequently the oxidized form of cytochrome b561 was re-reduced by ascorbate in the medium [2].

Biological context of CYB561

• Cytochrome b561 is not fatty acylated but acetylated at amino terminus in chromaffin vesicle membranes: an approach for the identification of posttranslational modification of transmembrane proteins [3].
• Thus only a fraction of the membrane potential effects the redox state of cytochrome b561 [4].
• Functional molecular mass of binding sites for [3H]dihydrotetrabenazine and [3H]reserpine and of dopamine beta-hydroxylase and cytochrome b561 from chromaffin granule membrane as determined by radiation inactivation [5].
• Structural basis for the electron transfer across the chromaffin vesicle membranes catalyzed by cytochrome b561: analyses of cDNA nucleotide sequences and visible absorption spectra [6].

Anatomical context of CYB561

• Only one major cleavage site at Lys191 was identified, indicating that cytochrome b561 was reconstituted into the membranes in an inside-out orientation irrespective of the modification with diethylpyrocarbonate [7].
• Subcellular fractionation of the cultured cells suggested that, after 3 or 4 h, the biotinylated DBH, which was still membrane-bound, was located in particulate material that also contained cytochrome b561, another major secretory granule membrane component [8].
• Cytochrome b-561 is located in the plasma membrane isolated from the chromaffin cells [9].
• The oxidation of cytochrome b561 by ATP was measured in submitochondrial particles inhibited by antimycin [4].
• To test this hypothesis, we investigated the distribution of dopamine-beta-hydroxylase and cytochrome b561 in bovine splenic nerve and nerve terminals in the vas deferens with an immunogold procedure after glycolmethacrylate embedding [10].

Associations of CYB561 with chemical compounds

• Properties of two distinct heme centers of cytochrome b561 from bovine chromaffin vesicles studied by EPR, resonance Raman, and ascorbate reduction assay [11].
• Reversely-oriented cytochrome b561 in reconstituted vesicles catalyzes transmembrane electron transfer and supports extravesicular dopamine beta-hydroxylase activity [7].
• This activity was enhanced significantly upon the addition of ferricyanide as a mediator between cytochrome b561 and dopamine beta-hydroxylase [7].
• From k0 and standard reduction potentials, the rate constant k-0 for the reduction of internal semidehydroascorbate by cytochrome b561 can be calculated [12].
• Since cytochrome b561 has been found in secretory vesicles associated with peptidyl glycine alpha-amidating monooxygenase, electron transfer to this enzyme was also examined [13].

Regulatory relationships of CYB561

• Pre-treatment of cytochrome b561 with diethylpyrocarbonate suppressed the reduction of extravesicular cytochrome c significantly, confirming that the reduction was not due to leakage of ascorbate from the vesicles [7].

Other interactions of CYB561

• We verified that purified cytochrome b561 can donate electron equivalents directly to cytochrome c. The purified cytochrome b561 was successfully reconstituted into cholesterol-phosphatidylcholine-phosphatidylglycerol vesicles by a detergent-dialysis and extrusion method [7].
• Whereas abundant gold labeling for cytochrome b561 was found over the entire surface of chromaffin granules, synaptophysin labeling was encountered mostly on vesicles adsorbed to granules [14].
• Under the same conditions, we found no variation in either the activities of other catecholamine biosynthetic enzymes (dopamine beta-hydroxylase and DOPA decarboxylase), or in metabolic enzymes such as lactate dehydrogenase and cytochrome c oxidase, and a decrease in the cellular content of chromogranin A and cytochrome b-561 [15].
• The fractions enriched in intact chromaffin granule markers, i.e. catecholamines, chromogranin A, chromogranin B and cytochrome b-561 were also enriched in labelled GTP-binding proteins [16].
• With the detergents tested the degree of solubilization decreased in the sequence cytochrome b-561 greater than cytochrome b5 greater than mitochondrial cytochrome(s) b and parallelled the effect of the detergents on light scattering and the phospholipid to protein ratio of the three membranes [17].

Analytical, diagnostic and therapeutic context of CYB561

• The topology of the reconstituted cytochrome b561 in the vesicle membranes was examined by treatment with trypsin followed by SDS-PAGE and MALDI-TOF-MS analyses [7].
• Distinct roles of two heme centers for transmembrane electron transfer in cytochrome b561 from bovine adrenal chromaffin vesicles as revealed by pulse radiolysis [2].
• When analyzed by isopycnic centrifugation, these sites cosedimented with catecholamine, chromogranin A, and cytochrome b561, in a peak with a density lighter than that from controls [18].
• An identical cytochrome b561 was found to be an integral component of both chromaffin vesicles from adrenal medulla and neurosecretory vesicles from posterior pituitary by spectrophotometric and immunological techniques [19].
• Cytochrome b561 from bovine adrenal medulla chromaffin granules has been purified by fast protein liquid chromatography chromatofocusing [13].

References