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Biomedical subjects

M Husain

Publications and source records attributed to M Husain.

At least 163 records · Page 9Linked to original sources
PubMed1986

Properties of Paracoccus denitrificans amicyanin.

Paracoccus denitrificans synthesizes an inducible, periplasmic, blue copper protein [Husain, M., & Davidson, V.L. (1985) J. Biol. Chem. 260, 14626-14629] that can be classified as an amicyanin on the basis of its ability to accept electrons from methylamine dehydrogenase. The amino acid composition and sequence of the 10 N-terminal residues of this protein have been determined. From these data, it is evident that amicyanin is structurally distinct from azurins as it contains no disulfide bond and an N-terminal sequence that is completely different from the highly conserved N-terminal azurin sequences. Dialysis of reduced amicyanin against potassium cyanide resulted in a nearly quantitative yield of apoamicyanin. Amicyanin and apoamicyanin exhibit fluorescence emission maxima at 314 nm when excited at 280 nm. Addition of 6 M guanidine hydrochloride shifts these emission maxima to 350 nm. The fluorescence intensity of apoamicyanin is 10-fold greater than that of amicyanin. Addition of copper to the apoprotein caused a stoichiometric quenching of fluorescence and restoration of visible absorbance with no concomitant change in absorbance at 280 nm. At least one cysteine residue, which reacts with 5,5'-dithiobis(2-nitrobenzoic acid) in apoamicyanin, does not react in the holoprotein, even in the presence of 6 M guanidine hydrochloride. Reductive and oxidative titrations of amicyanin indicate that it is a one-electron carrier. This amicyanin is also able to accept electrons from the methylamine dehydrogenase isolated from bacterium W3A1, which is taxonomically very different from P. denitrificans.

Amino Acid Sequence↗
PubMed1986

Preliminary X-ray crystallographic study of amicyanin from Paracoccus denitrificans.

Single crystals have been prepared of Paracoccus denitrificans amicyanin, a blue copper protein that serves as an electron acceptor for methylamine dehydrogenase. The crystals belong to the monoclinic space group P2(1), and have unit cell parameters a = 20.90 A, b = 56.61 A, c = 27.55 A and beta = 96.41. There is one molecule in the asymmetric unit. The crystals diffract to beyond 1.5 A resolution.

Bacterial Proteins↗
PubMed1986

Fatal thyrotoxic crisis.

Graves' disease is a form of hyperthyroidism. A rare complication of Graves' disease is thyrotoxic crisis. Although the crisis is frequently fatal, it is a distinctly unusual cause of sudden death. We investigated the case of a young woman with Graves' disease who died suddenly. Radioimmunoassay tests of thyroid function were used to establish the diagnosis.

Adult↗
PubMed1986

Electron transfer flavoprotein from Methylophilus methylotrophus: properties, comparison with other electron transfer flavoproteins, and regulation of expression by carbon source.

When grown on methylated amines as a carbon source, Methylophilus methylotrophus synthesizes an electron transfer flavoprotein (ETF) which is the natural electron acceptor of trimethylamine dehydrogenase. It is composed of two dissimilar subunits of 38,000 and 42,000 daltons and 1 mol of flavin adenine dinucleotide. It was reduced by trimethylamine dehydrogenase to a stable anionic semiquinone form, which could not be converted, either enzymatically or chemically, to the fully reduced dihydroquinone. This ETF exhibited spectral properties which were nearly identical to ETFs from bacterium W3A1, Paracoccus denitrificans, and pig liver mitochondria. M. methylotrophus ETF cross-reacted immunologically and enzymatically with the ETF of bacterium W3A1 but not with the other two ETFs. In M. methylotrophus and bacterium W3A1, ETF and trimethylamine dehydrogenase were each expressed during growth on trimethylamine and were each absent during growth on methanol.

Animals↗
PubMed1985

An inducible periplasmic blue copper protein from Paracoccus denitrificans. Purification, properties, and physiological role.

When grown on methylamine as a sole carbon source, Paracoccus denitrificans synthesizes a Type I blue copper protein which mediates electron transfer between methylamine dehydrogenase and cytochrome c. This blue copper protein does not serve as an electron acceptor for methanol dehydrogenase and is not synthesized by cells grown on methanol or succinate. The blue copper protein and methylamine dehydrogenase were localized in the periplasm of P. denitrificans, whereas formate dehydrogenase was cytoplasmic. The copper protein can be purified to high yield in a single step from the periplasmic subcellular fraction prepared from P. denitrificans. The purified protein contains a single 15,000-Da polypeptide chain and one copper atom/molecule and exhibits a pI of 4.8. The oxidized form of the protein absorbs strongly at 595 nm and weakly at 464 nm. The physical and physiological properties of this protein indicate that it is not an azurin, but representative of another class of blue copper proteins.

Bacterial Proteins↗
PubMed1985

Partial purification and characterization of glutaryl-coenzyme A dehydrogenase, electron transfer flavoprotein, and electron transfer flavoprotein-Q oxidoreductase from Paracoccus denitrificans.

Glutaryl-coenzyme A (CoA) dehydrogenase and the electron transfer flavoprotein (ETF) of Paracoccus denitrificans were purified to homogeneity from cells grown with glutaric acid as the carbon source. Glutaryl-CoA dehydrogenase had a molecular weight of 180,000 and was made up of four identical subunits with molecular weights of about 43,000 each of which contained one flavin adenine dinucleotide molecule. The enzyme catalyzed an oxidative decarboxylation of glutaryl-CoA to crotonyl-CoA, was maximally stable at pH 5.0, and lost activity readily at pH values above 7.0. The enzyme had a pH optimum in the range of 8.0 to 8.5, a catalytic center activity of about 960 min-1, and apparent Michaelis constants for glutaryl-CoA and pig liver ETF of about 1.2 and 2.5 microM, respectively. P. denitrificans ETF had a visible spectrum identical to that of pig liver ETF and was made up of two subunits, only one of which contained a flavin adenine dinucleotide molecule. The isoelectric point of P. denitrificans ETF was 4.45 compared with 6.8 for pig liver ETF. P. denitrificans ETF accepted electrons not only from P. denitrificans glutaryl-CoA dehydrogenase, but also from the pig liver butyryl-CoA and octanoyl-CoA dehydrogenases. The apparent Vmax was of similar magnitude with either pig liver or P. denitrificans ETF as an electron acceptor for these dehydrogenases. P. denitrificans glutaryl-CoA dehydrogenase and ETF were used to assay for the reduction of ubiquinone 1 by ETF-Q oxidoreductase in cholate extracts of P. denitrificans membranes. The ETF-Q oxidoreductase from P. denitrificans could accept electrons from either the bacterial or the pig liver ETF. In either case, the apparent Km for ETF was infinitely high. P. denitrificans ETF-Q oxidoreductase was purified from contaminating paramagnets, and the resultant preparation had electron paramagnetic resonance signals at 2.081, 1.938, and 1.879 G, similar to those of the mitochondrial enzyme.

Amino Acids↗
PubMed1984

Measurement of the oxidation-reduction potentials for one-electron and two-electron reduction of electron-transfer flavoprotein from pig liver.

Potentiometric titrations of pig liver electron-transfer flavoprotein (ETF) were performed at pH 7.5 and 4 degrees C, both in the reductive and oxidative directions. Reduction of ETF to the hydroquinone form required a total of two reducing equivalents/mol of ETF with the formation of sub-stoichiometric amounts of anionic semiquinone as an intermediate. The oxidation-reduction potentials for the two one-electron couples, oxidized ETF/ETF semiquinone and ETF semiquinone/fully reduced ETF, are +4 mV and -50 mV respectively. The overall midpoint potential for the two-electron couple (oxidized ETF/fully reduced ETF) is -23 mV.

Animals↗
PubMed1983

Electron transfer flavoprotein from pig liver mitochondria. A simple purification and re-evaluation of some of the molecular properties.

Electron transfer flavoprotein (ETF) from pig liver mitochondria has been purified to homogeneity by a three-step procedure with approx. 10-fold higher yields than previously reported. The purified ETF exhibits an absorption coefficient for the bound FAD of 13.5 mM-1.cm-1 at 436 nm and an isoelectric point of 6.75. Gel filtration, sodium dodecyl sulphate gel electrophoresis and flavin analysis indicate that pig liver ETF is a dimer, composed of non-identical subunits (Mr 38 000 and 32 000) with only one FAD/dimer. Anaerobic reduction by dithionite produces anionic flavin semiquinone as a stable intermediate and establishes the flavin to be the only redox-active chromophore in ETF.

Amino Acids↗
PubMed1983

Right coronary artery occlusion after acute proximal dissection (hematoma).

A known hypertensive presented to the hospital with sudden onset of chest pain and shock. ECG, cardiac enzymes, aortogram and echocardiogram were normal. Hemodynamic monitoring and radionucleotide angiogram demonstrated a severely dyskinetic right ventricle. Autopsy revealed proximal aortic dissection with extramural compression of right coronary artery, resulting in right ventricular dysfunction.

Acute Disease↗
PubMed1982

The effect of tetrahydrofolate on the reduction of electron transfer flavoprotein by sarcosine and dimethylglycine dehydrogenases.

Pig liver electron transfer flavoprotein (ETF) is rapidly reduced by sarcosine and dimethylglycine dehydrogenases to the anionic semiquinone form, the subsequent formation of the flavoquinol form being a much slower process. In the presence of tetrahydrofolate the yield of anionic semiquinone at the end of the rapid phase of reduction of ETF is only about 10% less than without tetrahydrofolate, as judged by e.p.r. spectroscopy. Tetrahydrofolate does not alter the rate of reduction of ETF by either sarcosine or dimethylglycine dehydrogenase. Nevertheless, it was clearly demonstrated that tetrahydrofolate is a substrate for both sarcosine and dimethylglycine dehydrogenases and is converted to N5,10-methylenetetrahydrofolate.

Dimethylglycine Dehydrogenase↗
PubMed1982

Malignant lymphoma of small cleaved lymphocytes of the follicular mantle zone.

We describe a highly unusual lymphocytic lymphoma. It appeared to originate in the mantle zones of hyperplastic follicles that had large reactive centers. The tumor cells in the mantle zone were small lymphocytes with cleaved or very irregular nuclei. They had coarse and abundant IgM, kappa surface immunoglobulin markers, and receptors for complement. The tumor involvement was generalized at the time of discovery. The diagnosis of a malignant lymphoma was initially made with difficulty because of the presence of reactive follicular centers as well as a polyclonal hypergammaglobulinemia and large numbers of interfollicular plasma cells and plasmacytoid lymphocytes containing all classes of immunoglobulin. However, 2 yr later, the follicular centers were replaced by tumor nodules composed of lymphocytes identical in appearance and immunologic type to those seen originally. This case illustrates that not all nodular lymphomas are follicular center cell (FCC) neoplasms and that morphological transformation from small round to small cleaved lymphocytes and a corresponding increase in surface immunoglobulins may take place in the follicular mantle zone. The patient had a high titer of antibody to Epstein-Barr virus (EBV) and a poor lymphocyte response to concanavalin A, but neither the tumor cells nor the plasmacytoid lymphocytes contained EBV DNA.

Female↗
PubMed1980

T-cell lymphomas of large cell type. A variety of malignant lymphomas: "histiocytic" and mixed lymphocytic-"histiocytic".

Clinical and morphologic features of seven T-cell lymphomas of the large cell type are described. The tumors were grouped into those with irregular (3 cases) and those with round and regular nuclei (4 cases). In both groups, variation in cell size, numerous histiocytes and vessels, and many mitoses were distinguishing features. In only 1 case in the round and regular nucleus group was there relatively little variation in cell size and a paucity of histiocytes. Abundant polyribosomes, long strands of rough endoplasmic reticulum, and lysosomal granules were prominent electron microscopic features in both groups of tumors. The clinical presentations and courses varied considerably, especially in patients with tumors of the round nucleus type. One patient presented initially with chronic lymphocytic leukemia, 1 with Lennert's lymphoma, another with bone marrow infiltration, and a fourth with subcutaneous tumors. Two patients with the round nucleus type are still alive one and a half and two years after the original diagnosis. Two patients died two years after the onset of symptoms. Each of the 3 patients with tumors of the irregular nucleus type had a rapid clinical course and died within ten months.

Aged↗