476
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Austen BM, Smith EL. Identification of a functional arginine residue involved in coenzyme binding by the NADP-specific glutamate dehydrogenase of Neurospora. J Biol Chem 1976; 251:5835-7. [PMID: 9404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The NADP-specific glutamate dehydrogenase (EC 1.4.1.4) of Neurospora crassa is inhibited by reaction with 1,2-cyclohexanedione which binds to arginine residues. With the 14C-labeled reagent, a peptide was isolated with the sequence: Gly-Gly-Leu-Arg-Leu-His-Pro-Ser-Val-Asn-Leu, corresponding to residues 78 through 88 in the protein. The arginine, residue 81, was present as N7,N8-(1,2-dihydroxycyclohex-1,2-ylene)-arginyl (or DHCH-arginine). Present evidence indicates that this arginine residue resides at or near the nicotinamide binding domain of the enzyme. Similar sequences are present in the bovine liver enzyme (EC 1.4.1.3) and the NAD-specific glutamate dehydrogenase of Neurospora (EC 1.4.1.2).
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477
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Brett M, Chambers GK, Holder AA, Fincham JR, Wootton JC. Mutational amino acid replacements in Neurospora crassa NADP-specific glutamate dehydrogenase. J Mol Biol 1976; 106:1-22. [PMID: 9517 DOI: 10.1016/0022-2836(76)90297-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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478
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Vega JM. A reduced pyridine nucleotides-diaphorase activity associated to the assimilatory nitrite reductase complex from Neurospora crassa. Arch Microbiol 1976; 109:237-42. [PMID: 136235 DOI: 10.1007/bf00446634] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The Neurospora crassa assimilatory NAD(P)H-nitrite reductase complex has associated a NAD(P)H-diaphorase activity. 1. This NAD(P)H-diaphorase activity can use either mammalian cytochrome c, 2,6--dichlorophenol-indophenol, ferricyanide, or menadione as electron acceptor from the reduced pyridine nucleotides, and requires flavin adenine dinucleotide for maximal activity. 2. It is inhibited by p-hydroxymercuribenzoate, 1 muM, and it is unaffected by cyanide, sulfite, or arsenite at concentrations which completely inhibit the NAD(P)H-nitrite reductase activity. 3. Flavin adenine dinucleotide specifically protects the NAD(P)H-diaphorase activities, but not the NAD(P)H-nitrite reductase activities, against thermal inactivation. 4. In vitro preincubation of the Neurospora crassa nitrite reductase complex with reduced pyridine nucleotides plus flavin adenine dinucleotide inactivates the NAD(P)H-nitrite reductase activities, but does not affect the NAD(P)H-diaphorase activities, indicating that this nitrite reductase inactivation occurs in the part of the enzyme that contain the nitrite reducing center.
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479
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Palacios R. Neurospora crassa glutamine synthetase. Purification by affinity chromatography and characterization of subunit structure. J Biol Chem 1976; 251:4787-91. [PMID: 7567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Neurospora crassa glutamine synthetase was purified to homogeneity by a procedure based on affinity chromatography. The enzyme is adsorbed to a matrix of anthranilic acid bound to Sepharose and eluted with AMP. Different experimental approaches indicate that the enzyme has an octameric structure formed by subunits of identical molecular weight.
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480
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Makoff AJ, Radford A. The location of the feedback-specific region with the pyrimidine-3 locus of Neurospora crassa. MOLECULAR & GENERAL GENETICS : MGG 1976; 146:247-51. [PMID: 187923 DOI: 10.1007/bf00701247] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The purimidine-3 locus of Neurospora crassa specifies two enzyme activities, pyrimidine-specific carbamyl phosphate synthetase (CPSpyr) and aspartate transcarbamylase (ATC). ATC is translationally distal. CPSpyr, but not ATC, is subject to feedback inhibition by uridine triphosphate (UTP). To investigate the location of the feedback-specific region within the locus, inhibition of a number of pyr-3 alleles by UTP was investigated. All CPS+ ATC- polar alleles, revertants of CPS- ATC- polar alleles, and 5-fluorouracil-resistant mutants had normal UTP response. The location of the feedback-specific region is in or close to the CPS-specific region.
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481
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Gore MG, Iwatsubo M. Biphasic interactions between a Neurospora crassa glutamate dehydrogenase and reduced nicotinamide-adenine dinucleotide phosphate. Biochem Soc Trans 1976; 4:612-4. [PMID: 12047 DOI: 10.1042/bst0040612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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482
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Arron GP, Henry L, Palmer JM, Hall DO. Superoxide dismutases in mitochondria from Helianthls tuberosus and Neurospora crassa. Biochem Soc Trans 1976; 4:618-20. [PMID: 137151 DOI: 10.1042/bst0040618] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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483
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484
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Hasunuma K, Toh-e A, Ishikawa T. Control of the formation of extracellular ribonuclease in Neurospora crassa. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 432:223-36. [PMID: 5154 DOI: 10.1016/0005-2787(76)90164-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
A finding was made that a species of ribonuclease is released into mycelial culture media when a wild-type strain of Neurospora crassa was grown on limiting amounts of phosphate. The ribonuclease activity in the fully derepressed state extends to about 60 to 100 fold of that in the repressed state. The synthesis of the ribonuclease was inhibited by the addition of rifampicin, cycloheximide or orthophosphate. Three molecular species of the ribonuclease were found. Two enzyme fractions showing larger molecular weights were suspected to be aggregates containing the enzyme showing the smallest molecular weight (molecular weight of 10 300). All three fractions showed pH optima of around 7, preferential hydrolysis of polyguanylic acid and poor hydrolysis of guanosine 2',3',-cyclic monophosphate. These characteristics were the same as those of ribonuclease N1, and it was suggested that ribonuclease N1 is a repressible extracellular enzyme. Mutations in the genes nuc-1 and nuc-2 caused loss of ability to derepress this enzyme, but heterokaryon between them partially restored the ability. The nuc-1 mutation was epistatic to the nuc-2 alleles which are partly constitutive in the ribonuclease production.
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485
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Nelson RE, Selitrennikoff CP, Siegel RW. Developmental regulation of nicotinamide adenine dinucleotide (phosphate) glycohydrolase in Neurospora crassa. Dev Biol 1976; 50:122-33. [PMID: 131723 DOI: 10.1016/0012-1606(76)90072-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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486
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Chang HC, Sorger GJ. Effect of ammonium ions on the induction of nitrite reductase in Neurospora crassa. J Bacteriol 1976; 126:1002-4. [PMID: 131122 PMCID: PMC233241 DOI: 10.1128/jb.126.2.1002-1004.1976] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Results with strain am-la, a glutamate dehydrogenaseless mutant, showed that ammonium ions must first be metabolized in order to repress nitrite reductase in Neurospora.
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487
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Kapoor M, O'Brien M, Braun A. Modification of the regulatory properties of pyruvate kinase of Neurospora by growth at elevated temperatures. CANADIAN JOURNAL OF BIOCHEMISTRY 1976; 54:398-407. [PMID: 6132 DOI: 10.1139/o76-058] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Pyruvate kinase (EC 2.7.1.40) was isolated from Neurospora crassa mycelium grown at 28 degrees C (PK-28) and at 42 degrees C (PK-42). The regulatory properties, particularly the response towards the allosteric effector fructose 1,6-diphosphate (FDP), was different in the two enzymes. PK-28 showed an activation by FDP but PK-42, under comparable conditions, appeared to be activated by low concentrations of FDP and inhibited by higher ones. For PK-28, complex formation with FDP results in a lowering of the isoelectric point from 6.40 to 5.50, representing the pI of the unliganded enzyme and that of the complex, respectively. In contrast to this, PK-42 exhibits a weak binding to FDP as suggested by a lack of decrease in the isoelectric point on treatment with comparable concentrations of FDP. Studies with quenching of aromatic residue fluorescence of PK-28 and PK-42, following binding of FDP, indicate that although this ligand binds to both types of enzymes the affinity for the two is vastly different. Dissociation constants of 9.3 muM and 0.1 mM were calculated for the binding of FDP to PK-28 and PK-42, respectively. It is concluded that growth at elevated temperatures induced a conformational change in the pyruvate kinase leading to partial desensitization of the allosteric site. The nature of the factor(s) responsible for this change is not understood at present.
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488
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Scarborough GA. The neurospora plasma membrane ATPase is an electrogenic pump. Proc Natl Acad Sci U S A 1976; 73:1485-8. [PMID: 131943 PMCID: PMC430321 DOI: 10.1073/pnas.73.5.1485] [Citation(s) in RCA: 104] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Biochemicalical evidence is presented which demonstrates that the Neurospora crassa plasma membrane ATPase (ATP phosphohydrolase, EC 3.6.1.3) is an electrogenic pump. The electrical potential across the Neurospora plasma membrane, as monitored by [14C]SCN- uptake by isolated Neurospora plasma membrane vesicles, is markedly increased interior positive under conditions of ATP hydrolysis catalyzed by plasma membrane ATPase. [14C]SCN- uptake by the vesicles is minimal in the presence of Tris phosphate, Tris phosphate plus Mg+2, Tris ADP plus Mg+2, and Tris ATP, but is markedly stimulated in the presence of Tris ATP plus Mg+2.
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489
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Holm K, Nilheden E, Kolmark HG. Genetic and enzymatic analysis of a glycerol kinase deficient mutant in Neurospora crassa. MOLECULAR & GENERAL GENETICS : MGG 1976; 144:11-15. [PMID: 177854 DOI: 10.1007/bf00277297] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Genetic analysis showed that the glycerol non-utilizing isolate gly-u(234) of Neurospora crassa is derived by mutation in a nuclear gene situated in the right arm of linkage group I, about 2.2 cross-over units distal to ad-9 and 11 units proximal to nit-1. Enzymatic testings using a radiochemical method indicate that the mutant is deficient for the enzyme glycerol kinase. The radiochemical testings further indicate that the mutation has inactivated an inducible glycerol kinase, while a low residual activity may be due to a second, basal and non-inducible glycerol kinase, in accordance with a proposal by North (1973, 1974) that Neurospora has two glycerol kinases with these properties.
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490
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de Goede GW, Samallo J, Holtrop M, Scherphof GL. Lysophospholipase activity in cell-wall fragments contaminating mitochondrial fractions of Neurospora crassa. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 424:195-203. [PMID: 3219 DOI: 10.1016/0005-2760(76)90188-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Crude mitochondrial preparations from Neurospora crassa contain high levels of lysophospholipase (EC 3.1.1.5) activity when assayed with lysophosphatidylcholine as a substrate. In mitochondria purified by centrifugation on a sucrose-density gradient this activity is virtually absent. The enzyme was shown to be linked to a contaminating cell fraction which mainly consists of cell-wall material as was demonstrated by electron microscopy and chemical analysis. The enzyme has no absolute Ca2+ requirement but it is slightly stimulated by 10 mM CaCl2. The pH optimum is 5.8 in presence of CaCl2 and is shifted to 4.2 when EDTA is present. In contrast to other lysophospholipases this enzyme is only slightly inhibited by deoxycholate. This detergent is able to release part of the lysophospholipase activity from the wall fragments without producing an increase in specific activity. The enzyme is possibly secreted by the cells as high lysophospholipase activities were also found in the culture medium.
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491
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North MJ. Increase of enzyme activities in Neurospora crassa during incubation at low temperatures. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 422:309-15. [PMID: 129162 DOI: 10.1016/0005-2744(76)90142-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The effect of lowering the incubation temperature of sucrose-grown cultures of Neurospora crassa on the level of various enzyme activities was investigated. Of twelve inducible/derepressible activities studied, three, in addition to glycerol kinase, were found to increase during 48 h of incubation at 4-6 degrees C: trehalase (increase in specific activity of 3-10-fold), beta-glucosidase (6-12-fold) and beta-N-acetylglucosaminidase (4 to 6-fold). The maximum increases occurred at 6 degrees C and no increases took place in mycelia incubated at 0 degrees C. The kinetics of the changes in activity were markedly different from those observed previously with glycerol kinase. The increases were inhibited by cycloheximide. Trehalase, beta-glucosidase and beta-N-acetylglucosaminidase activities were not rapidly lost when cultures incubated at 6 degrees C were returned to 26 degrees C.
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492
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North MJ. Influence of the carbon source on glycerol kinase activity in Neurospora crassa. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 422:316-25. [PMID: 174743 DOI: 10.1016/0005-2744(76)90143-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The level of glycerol kinase activity in Neurospora crassa was shown to change in response to resuspension of sucrose-grown mycelia in fresh medium containing a new carbon source: the magnitude of the change depended on the new carbon source provided. Certain carbon sources, such as glucose and fructose, inhibited the small increase that occurred in the absence of any carbon source. Others, and in particular deoxyribose, galactose, glycerol and ribose, greatly enhanced this increase. The activity induced by deoxyribose and galactose had the same stability, both in vivo and in vitro, as that induced by glycerol, and as that induced by incubation of Neurospora cultures at low temperatures. The inhibitory carbon sources, such as glucose and fructose, also restricted the increases induced by deoxyribose, galactose and glycerol: they had more effect on the increases induced by glycerol and deoxyribose than on that induced by galactose. The increase in activity that occurs at low temperature was also inhibited by glucose and sucrose.
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493
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494
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Welch GR, Gaertner FH. Coordinate activation of a multienzyme complex by the first substrate. Evidence for a novel regulatory mechanism in the polyaromatic pathway of Neurospora crassa. Arch Biochem Biophys 1976; 172:476-89. [PMID: 130831 DOI: 10.1016/0003-9861(76)90101-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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495
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Fincham JR. Recombination in the AM gene of Neurospora crassa--a new model for conversion polarity and an explanation for a marker effect. Heredity (Edinb) 1976; 36:81-9. [PMID: 130365 DOI: 10.1038/hdy.1976.9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
It is argued that polarised intragenic recombination is not necessarily due to hybrid DNA extending into the gene for variable distances from one side; it can as well be explained by hybrid DNA usually covering the whole gene, the two complementary DNA strands of the gene having unequal chances of undergoing the interchromatid transfer involved in hybrid DNA formation, and excision from base-pair mismatches proceeding predominantly in one chemical direction (perhaps 5' to 3'). This alternative model for polarity is thought to be in better accord with the behaviour of flanking markers in the am data, which appears to show that conversion-associated crossing-over can occur with almost equal likelihood on either side of the gene (a feature previously held to support negative interference--Fincham, 1974). It also provides an explanation for an unusual marker effect involving two am mutational sites separated by only three base pairs. The nature of the sites (defined by amino acid replacement analysis) is such that one forms a purine-purine mismatch on the same chromatid as the other forms a pyrimidine-pyrimidine mismatch, and vice versa. They show an approximately two-fold difference in recombination frequencies in crosses to other am mutants mapping to the left, and a difference of similar magnitude, but opposite sign, in crosses to mutants mapping to the right.
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496
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Abstract
During the germination and growth of Neurospora conidia, amino acid permease systems I (neutral) and II (general) increase in specific activity. System III (basic) decreases in specific activity with the onset of germination. System I shows two peaks of activity during the logarithmic phase of growth. One peak occurs at 6 h, the other at 12 h of growth. Both peaks are abolished in the mtr mutant. Both peaks have a Km for phenylalanine of 40 muM. The peaks of system I activity appear to correlate with morphological changes.
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497
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Abramsky T, Tatum EL. Differential inhibition of branching enzyme in a morphological mutant and in wild type Neurospora. Influence of carbon source in the growth medium. Biochim Biophys Acta Gen Subj 1976; 421:106-14. [PMID: 129159 DOI: 10.1016/0304-4165(76)90174-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
1. A morphological mutant of Neurospora crassa, smco 9, (R2508) that exhibits colonial morphology when grown on sucrose or on maltose, showed a partial reversal of this morphology toward that of the wild type when it was grown on potato starch or on isomaltose. 2. A common feature of both potato starch and isomaltose is the presence of alpha-1, 6 glucosidic linkages. This suggested that these morphological effects might be due to differences in alpha-1,4 glucan: alpha-1,4 glucan 6 glycosyltransferase, (EC 2.4.1.18) commonly known as "the branching enzyme". 3. The branching enzyme was purified from wild type, Neurospora crassa, and from the semicolonial mutant, R2508, both grown on sucrose or on potato starch. It has a molecular weight of 140,000 as estimated by gel filtration on a Bio Gel A 1.5 m column. This enzyme plus phosphorylase a in an unprimed reaction catalyzes the synthesis of a branched polysaccharide in vitro. 4. No branching enzyme activity was apparent in extracts of the mutant R2508, grown on potato starch until a thermolabile inhibitor was removed by fractionation on a DEAE column. 5. This inhibitor has a molecular weight greater than 100,000 as estimated on a P-100 polyacrylamide gel column. The specificity of the inhibitor is not absolute in that it inhibits glycogen synthetase in addition to the branching enzyme in Neurospora.
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498
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Nomura A. [Endonucleases from plants (author's transl)]. TANPAKUSHITSU KAKUSAN KOSO. PROTEIN, NUCLEIC ACID, ENZYME 1976; 21:14-23. [PMID: 2949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/16/2023]
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499
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Scott WA, Mahoney E. Defects of glucose-6-phosphate and 6-phosphogluconate dehydrogenases in Neurospora and their pleiotropic effects. CURRENT TOPICS IN CELLULAR REGULATION 1976; 10:205-36. [PMID: 3390 DOI: 10.1016/b978-0-12-152810-2.50012-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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500
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Miller RW. A high molecular weight dihydro-orotate dehydrogenase of Neurospora crassa. Purification and properties of the enzyme. CANADIAN JOURNAL OF BIOCHEMISTRY 1975; 53:1288-300. [PMID: 130199 DOI: 10.1139/o75-175] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Some of the unusual molecular and catalytic properties of a high molecular weight dihydro-orotate dehydrogenase (DHOD) from Neurospora crassa have been determined. Comparison of the properties of this enzyme with the properties of the soluble biosynthetic enzyme of prokaryotes has revealed several important differences. The fungal enzyme is located in a mitochondrial membrane in a position consistent with linkage with the respiratory chain through ubiquinone (Miller, R. W.: Arch. Biochem, Biophys. 146, 256-270 (1971)). Release of the enzyme from the membrane results in a solubilized protein complex containing bound lipids and inactive hydrophobic proteins. Non-specific protein aggregation is minimized during purification by Triton-X-100 and phospholipase treatments. The catalytically active enzyme has an apparent molecular weight of 210 000. In contrast to soluble DHOD preparations the high molecular weight enzyme has no endogenous dihydro-orotate oxidase (EC 1.3.3.1) activity and is relatively insensitive to inactivation by sulfhydryl-reactive reagents in the presence of dihydro-orotate (DHO). The enzyme activity is highly sensitive to conditions causing oxidation of flavin mononucleotide (FMN). The activity cannot be restored by cysteine or other means. FMN is present in all purified preparations in a bound, non-fluorescent (reduced) form until dihydro-orotic acid is removed or oxidized. Catalytic efficiency of the purified enzyme was 12 000 mol DHO oxidized per minute per mole FMN. This high turnover rate is due in part to the small flavin content of the purified enzyme, equivalent to 1 mol FMN per 120 000 g of catalytically active protein. Iron was detected in the purified enzyme by atomic absorption spectroscopy but labile sulfide was absent. Thenoyltrifluoroacetone, an iron chelator, only partially inhibited DHO oxidation regardless of electron acceptor. Fatty acids interact with a hydrophobic site of the enzyme in non-competitive fashion but under certain conditions appear to significantly alter the Km for ubiquinone. Orotate, by comparison, is a purely competitive inhibitor. Both types of inhibitor may function to regulate the biosynthesis of orotate in vivo. Superoxide anion is not produced in significant quantities by the DHO-reduced enzyme unless both ubiquinone and a suitable single electron carrier such as phenazine methosulfate are present. DHOD has been proposed as a source of superoxide anion in mammalian mitochondria (Forman, H. J. & Kennedy, J. A.: J. Biol. Chem. 250, 4322-4326 (1975)).
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