[Method of multilocus enzyme electrophoresis for typing Neisseria meningitidis serogroup A in China and it's significance in epidemiology]

A new, more perfect taxonomic method the multilocus enzyme electrophoresis has recently been developed to type Neisseria meningitidise serogroup A strains in China isolated from 1956-1987 and to study the epidemiological relationship of the types. 183 strains could be divided into 24 ET types, among which ETs, ET18 were found predominant in epidemics occurred in last two decades respectively. Different predominant ET types were found in different epidemic period and only one predominant ET type existed in each period. The cases and carriers occurred in the interepidemic stage and in some places. Their strains belonged to some endemic ET types.

Microbial metabolism of quinoline and related compounds. VIII. Xanthine dehydrogenase from a quinoline utilizing Pseudomonas putida strain

The xanthine dehydrogenase from Pseudomonas putida 86 was purified 68-fold to homogeneity with 47% recovery. SDS-polyacrylamide gel electrophoresis of the enzyme revealed two protein bands corresponding to an Mr of 87,000 and 52,000. The Mr of the native enzyme was calculated to 550,000 by gel chromatography. The enzyme contained 4 atoms of molybdenum, 16 atoms of iron, 16 atoms of acidlabile sulphur and 4 molecules of FAD. Due to the composition of the cofactors the xanthine dehydrogenase belongs to the class of molybdo-iron/sulphur-flavoproteins. Form A, an oxidation product of the molybdenum cofactor, was identified. Methanol and cyanide were effective inhibitors.

Induction of lung lysyl oxidase activity and lysyl oxidase protein by exposure of rats to cadmium chloride: properties of the induced enzyme

Inspiration of CdCl2 results in a focally fibrotic response in rat lungs and markedly increases the activity of lung lysyl oxidase. Western blot analyses of urea-extractable rat lung proteins revealed that the levels of an immunoreactive, 32,000-Da protein were markedly increased in the cadmium-exposed rat lung tissue, consistent with the induction of lysyl oxidase protein. Anion exchange chromatography revealed low levels of multiple peaks of catalytically functional lysyl oxidase in control rat lung extracts, while the profile of cadmium-exposed rat lung extracts displayed markedly elevated levels of multiple peaks of enzyme activity indicating that the charge heterogeneity is expressed in the activated enzyme. The cadmium-induced enzyme was purified as a species of 32 kDa, without resolving individual ionic variants. The catalytic and physical properties of the isolated enzyme were very similar to those of previously well characterized basal enzyme of bovine aorta, including the presence of a pyrroloquinoline quinone-like carbonyl cofactor. The copper and cadmium content of the cadmium-induced enzyme indicated little if any replacement of tightly-bound copper by cadmium in the exposed lung.

Failure to verify the presence of pyrroloquinoline quinone (PQQ) in bovine plasma amine oxidase by gas chromatography/mass spectrometry

The presence of covalently bound pyrroloquinoline quinone (PQQ) in bovine plasma amine oxidase (BPAO) was examined by the use of gas chromatography/mass spectrometry. The enzyme was subjected to proteolysis with proteinase in the presence of [U-13C]PQQ as an internal standard. After isolation and derivatization of PQQ with phenyltrimethylammonium hydroxide, molecular peaks at m/z 448 and 462 were used for detection of PQQ and [U-13C]PQQ, respectively, by selected ion monitoring (SIM). In the SIM profile, although the sample extract obtained from BPAO treated with proteinase clearly showed the peak at m/z 462 for the internal standard, there were no peaks detectable at m/z 448, showing the absence of PQQ in the proteolysis digest of BPAO. Thus, our results do not support the claim that BPAO contains covalently bound PQQ in its structure.

Microbial metabolism of quinoline and related compounds. VII. Quinoline oxidoreductase from Pseudomonas putida: a molybdenum-containing enzyme

The quinoline oxidoreductase from Pseudomonas putida was purified 50-fold to homogeneity with 21% recovery, using ammonium sulfate precipitation, hydrophobic interaction-, anion exchange-, and gel chromatography. The Mr of the native enzyme was calculated to be 300,000 by gel filtration. SDS-polyacrylamide gel electrophoresis of the enzyme revealed three protein bands corresponding to Mr 85,000, 30,000 and 20,000. The enzyme contained 8 atoms of iron, 8 atoms of acid-labile sulfide, 2 molecules of FAD, and the molybdenum cofactor, molybdopterin. Besides quinoline, the quinoline oxidoreductase also catalysed the conversion of 5-, 6-, 7- and 8-hydroxyquinoline and 8-chloroquinoline to the corresponding 2-oxo compounds. The incorporated oxygen atom was derived from water. Cyanide and methanol were effective inhibitors.

Soybean lipoxygenase-1 is not a quinoprotein

Soybean lipoxygenase-1 was reinvestigated with respect to its quinoprotein nature. It has been reported previously that soybean lipoxygenase-1 contains pyrroloquinoline quinone as the organic cofactor. Because spectroscopic data were found to be inconsistent with the evidence presented in [1], we sought to reproduce the published data by carefully following the procedures described in [1] and supplementing them with new analytical results. The combined data lead us to conclude that soybean lipoxygenase-1 is not a quinoprotein.

Occurrence and tissue distribution of both NADH- and NADPH-linked aquacobalamin reductases in some vertebrates

To elucidate the synthesis of cobalamin coenzymes in view of comparative biochemistry, tissue distribution of activity of aquacobalamin reductase [EC 1.6.99.8] catalyzing the reduction of hydroxocobalamin to cob(II)alamin was studied in some vertebrates. Activity of NADH- or NADPH-linked aquacobalamin reductase (or both) was found in some tissues of monkey, rat, cow, hog, chicken, fish, and frog. The liver homogenates of these vertebrates contained both NADH- and NADPH-linked enzymes. Monkey and rat livers accounted for more than 80% of total activities of both NADH- and NADPH-linked enzymes. Ratios of activities of the liver NADH- and NADPH-linked enzymes were above 1.0 in some land animals (monkey, rat, cow, and hog) but below 1.0 in water animals (sea and freshwater fishes). These different ratios are presumably due to the difference in the metabolisms of cobalamin and/or in the other cellular components between land and water animals.

Widespread occurrence of 2-acetylthiazole-4-carboxylic acid in biological material

2-Acetylthiazole-4-carboxylic acid was shown to be widely distributed in all organisms tested, which included members of the eukaryotes, archaebacteria, and eubacteria. This thiazole, which was identified and quantitated as the methyl ester methoxyamine derivative, was found in these organisms at levels of from 27 to 1100 nmol/g dry weight (d.wt) of tissue. On the basis of its widespread occurrence, the levels at which it occurs in these organisms, and its chemical structure, which contains a reactive carbonyl group, it is proposed that this compound is a previously undescribed coenzyme.

The redox-cycling assay is not suited for the detection of pyrroloquinoline quinone in biological samples

Based on the results of the so-called redox-cycling assay it has been claimed that various common foods and beverages as well as mammalian body fluids and tissues contain substantial quantities (microM) of free PQQ [M. Paz et al. (1989) in: PQQ and Quinoproteins (J.A. Jongejan and J.A. Duine, eds.) Kluwer Academic Publishers, Dordrecht, pp. 131-143 and J. Killgore et al. (1989) Science 245, 850-852]. However, by investigating samples from such sources with a biological assay of nM sensitivity, we could not confirm these claims. Analysis of the samples with procedures that proved adequate for the detection of PQQ adducts and conjugates gave equally negative results. To account for the positive response in the redox-cycling assay, as opposed to the negative results obtained by other methods, a search was made for those substances in these samples that caused the false-positive reactions. It was found that a number of commonly occurring biochemicals like ascorbic and dehydroascorbic acid, riboflavin and to a lesser extent pyridoxal phosphate, gave a positive response in the redox-cycling assay. The amounts of these interfering substances that were determined in the samples by independent methods could well explain the response. In separate experiments it was found that the effect of PQQ added to biological samples was obscured over an appreciable range of concentrations. For these reasons it must be concluded that the redox-cycling assay is not suited for the detection of PQQ in these samples. Any claims that are based on the results of this method should be disregarded.

Studies on the active site of pig plasma amine oxidase

Amine oxidase from pig plasma (PPAO) has two bound Cu2+ ions and at least one pyrroloquinoline quinone (PQQ) moiety as cofactors. It is shown that recovery of activity by copper-depleted PPAO is linear with respect to added Cu2+ ions. Recovery of e.s.r. and optical spectral characteristics of active-site copper parallel the recovery of catalytic activity. These results are consistent with both Cu2+ ions contributing to catalysis. Further e.s.r. studies indicate that the two copper sites in PPAO, unlike those in amine oxidases from other sources, are chemically distinct. These comparative studies establish that non-identity of the Cu2+ ions in PPAO is not a requirement for amine oxidase activity. It is shown through the use of a new assay procedure that there are two molecules of PQQ bound per molecule of protein in PPAO; only the more reactive of these PQQ moieties is required for activity.

Evidence that 31P NMR is a sensitive indicator of small conformational changes in the coenzyme of aspartate aminotransferase

The pH dependence of 31P-NMR spectra of pig cytosolic aspartate aminotransferase, containing either N-(5'-phosphopyridoxyl)-L-aspartate or pyridoxal 5'-deoxymethylenephosphonate in place of the normal coenzyme pyridoxal 5'-phosphate, has been analysed. The chemical shifts of phosphopyridoxylaspartate and of pyridoxal 5'-deoxymethylenephosphonate model Schiff base in free solution show pK values of 6.3 and 7.4, attributable to the second deprotonation step of phosphate and phosphonate, respectively. However, these compounds behave very differently when bound to apoaspartate aminotransferase. 31P-NMR spectra of these enzyme derivatives indicate that the phosph(on)ate group remains dianionic throughout the pH range 4-8.5. A clear correlation between apparent pK values obtained from spectrophotometric titration of the coenzyme chromophore and those obtained by 31P NMR indicates that the same ionisation is being reported by both methods. The data are interpreted, on the basis of available crystallographic structures of chicken mitochondrial aspartate aminotransferase, to indicate that in each case the alteration in 31P chemical shift results from a conformational change in the coenzyme 5' side chain, in which one of the structures involves a near-eclipsed pair of bonds. Such a stressed conformation produces slight alterations in bond angles around the phosphorus atom, which in turn cause the observed change in 31P chemical shift. The evidence is taken to indicate that in this case 31P NMR is a sensitive reporter of stress in enzyme-bound pyridoxal 5'-phosphate and its derivatives.

[Study of coenzyme reorientation in the active center of tryptophanase by linear dichroism method]

Tryptophanase from E.coli was oriented in a compressed slab of polyacrylamide gel and its linear dichroism (LD) and absorption spectra were measured. The free enzyme displays four LD bands at 305, 340, 425 and 490 nm. Two bands at 340 and 425 nm belong to the internal coenzyme-lysine aldimine. The 305 nm band apparently belongs to an aromatic amino acid residue; the sign and form of this band are changed upon the enzyme reaction with substrate analogs. The 490 nm band is present in the LD spectra of holo- and apoenzyme and disappears after treatment with NaBH4. It is suggested that the 490 nm band belongs to a quinoid enzyme subform. The reaction of tryptophanase with threo-beta-phenyl-DL-serine and L-threonine leads to formation of the external aldimine with a strong absorption band at 420-425 nm. The reduced LD (delta A/A) in this band is one order of magnitude greater than that in the 420 nm of the free enzyme. The complex with D-alanine is characterized by an intermediate LD value in the 425 nm band. In the presence of indole this complex displays the same LD as that observed with beta-phenylserine. The reaction of tryptophanase with L-alanine and oxindolyl-L-alanine leads to formation of the quinoid intermediate with a 500 nm absorption band. The LD value in this band differs from those in the absorption bands of the free enzyme. It is concluded that reorientations of the coenzyme occur in the course of the tryptophanase reaction.

Interaction between pyridine nucleotide coenzymes and heme proteins as a possible source of error in assay of activities of coenzyme-linked enzyme

The ultraviolet absorbance spectra of pyridine nucleotide coenzymes change in the presence of heme-containing proteins. The positions of each of the two main absorbance peaks of NADH are shifted progressively towards shorter wavelengths in the presence of increasing concentrations of hemoglobin, and the third peak, at 220 nm, disappears altogether. Similar changes are seen in the spectra of NAD+ and NADPH, and similar effects on these spectra are produced by myoglobin and cytochrome c, but not by comparable concentrations of albumin. The spectral shifts are generally accompanied by a decreased peak height. This finding may help explain problems reported by previous workers in the measurement of the activity of enzymes such as transketolase or lactate dehydrogenase in erythrocyte hemolysates. Errors may be considerable if allowance is not made for this effect, especially if the concentration of heme protein in the spectrophotometer cuvette much exceeds 1 g/L. The interaction appears to indicate some form of bonding, occurring generally between pyridine nucleotide coenzymes and the heme group in proteins. We relate the findings to measurement of activities of pyridine nucleotide-linked enzymes in erythrocyte lysates and in plasma containing myoglobin after muscle breakdown.

PQQ, the elusive coenzyme

The recently discovered redox coenzyme, PQQ (methoxatin), is widely distributed. Quantitation of protein-bound PQQ has been difficult, but unique redox cycling reactions, which reflect its striking biological properties, reveal trace amounts. PQQ is a potential target for drugs.

Conformational changes in the active site of tryptophanase revealed by the circular dichroism method

Tryptophanase from E. coli displays positive CD in the coenzyme absorption bands at 337 and 420 nm. Breaking of the internal coenzyme-lysine imine bond upon reaction with hydroxylamine or amino-oxyacetate is accompanied by a strong diminution of the positive CD. Interaction of tryptophanase with L-threonine and beta-phenyl-DL-serine(threo form) leads to a decrease in absorbance at 337 nm and to an increase at 425 nm. This is associated with inversion of the CD sign, i.e. with disappearance of the positive CD in the 420-nm band and its replacement by a negative CD. L-Phenylalanine, alpha-methyl-DL-serine and D-alanine cause an increase in absorbance at 425-430 nm and a diminution of the positive CD in this band. In the presence of D-alanine and indole a negative CD appears in the 400-450 nm region. It is inferred that an external coenzyme-quasisubstrate aldimine is formed on interaction of the above amino acids with the enzyme. L-Alanine and oxindolyl-L-alanine evoke an intense narrow absorption band at 500 nm ascribed to a quinonoid intermediate; a positive CD is observed in this band. The dissymmetry factor delta A/A in the 500-nm band is much smaller than that in the absorption bands of the unliganded enzyme. Inversion of the CD sign on formation of the external aldimine and diminution of the dissymmetry factor in the quinonoid band indicate that reorientations of the coenzyme occur in the course of the catalytic action of tryptophanase.

Vitamin contents of archaebacteria

The levels of six water-soluble vitamins of seven archaebacterial species were determined and compared with the levels found in a eubacterium, Escherichia coli. Biotin, riboflavin, pantothenic acid, nicotinic acid, pyridoxine, and lipoic acid contents of Halobacterium volcanii, Methanobacterium thermoautotrophicum delta H, "Archaeoglobus fulgidus" VC-16, Thermococcus celer, Pyrodictium occultum, Thermoproteus tenax, and Sulfolobus solfataricus were measured by using bioassays. The archaebacteria examined were found to contain these vitamins at levels similar to or significantly below the levels found in in E. coli. Riboflavin was found at levels comparable to those in E. coli. Pyridoxine was as abundant among the archaebacteria of the methanogenhalophile branch as in E. coli. It was only one-half as abundant in the sulfur-metabolizing branch. "A. fulgidus," however, contained only 4% as much pyridoxine as E. coli. Nicotinic and pantothenic acids were approximately 10-fold less abundant (except for a 200-fold-lower nicotinic acid level in "A. fulgidus"). Nicotinic acid may be replaced by an 8-hydroxy-5-deazaflavin coenzyme (factor F420) in some archaebacteria (such as "A. fulgidus"). Compared with the level in E. coli, biotin was equally as abundant in Thermococcus celer and Methanobacterium thermoautotrophicum, about one-fourth less abundant in P. occultum and "A. fulgidus," and 25 to over 100 times less abundant in the others. The level of lipoic acid was up to 20 times lower in H. volcanii, Methanobacterium thermoautotrophicum, and Thermococcus celer. It was over two orders of magnitude lower among the remaining organisms. With the exception of "A. fulgidus," lipoic acid, pantothenic acid, and pyridoxine were more abundant in the members of the methanogen-halophile branch of the archaebacteria than in the sulfur-metabolizing branch.

[Study of the reorientation of coenzyme in active sites of aspartate-aminotransferase isoenzymes using linear dichroism method]

Cytosolic and mitochondrial pig aspartate aminotransferases (cAAT and mAAT) and chicken cAAT were oriented in a compressed slab of polyacrylamide gel. Linear dichroism (LD) spectra of the pyridoxal and pyridoxamine forms of AATs and of complexes of the pyridoxal form with substrate analogues have been recorded. The tilt angles of the coenzyme at the intermediary steps of the transamination reaction have been calculated on the basis of reduced LD values (delta A/A), atomic coordinates of the coenzyme and directions of the transition dipole moments in the coenzyme ring. It was assumed that rotation of the coenzyme ring occurs around the C2-C5 axis in all cases except the enzyme complex with glutarate: in the latter case the direction N1-C4 was assumed to be a rotation axis. It has been found that formation of the enzyme complex with glutarate and protonation of the internal aldimine induce dissimilar reorientations of the coenzyme. As a result of protonation, the coenzyme tilts by 27 degrees in cAAT and 13 degrees in mAAT. Formation of the external aldimine with 2-methylaspartate is accompanied by tilting of the coenzyme ring by 44 degrees in cAAT and 39 degrees in mAAT. For the quinonoid complex with erythro-3-hydroxyaspartate, the tilt angles were found to be 63 degrees in cAAT and 53 degrees in mAAT. It was inferred that the basic features of the active site dynamics are similar in three AATs studied. The differences in the coenzyme tilt angles between cAAT and mAAT might be linked to catalytic peculiarities of the isoenzymes.

Purification and properties of Escherichia coli dimethyl sulfoxide reductase, an iron-sulfur molybdoenzyme with broad substrate specificity

Dimethyl sulfoxide reductase, a terminal electron transfer enzyme, was purified from anaerobically grown Escherichia coli harboring a plasmid which codes for dimethyl sulfoxide reductase. The enzyme was purified to greater than 90% homogeneity from cell envelopes by a three-step purification procedure involving extraction with the detergent Triton X-100, chromatofocusing, and DEAE ion-exchange chromatography. The purified enzyme was composed of three subunits with molecular weights of 82,600, 23,600, and 22,700 as identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native molecular weight was determined by gel electrophoresis to be 155,000. The purified enzyme contained 7.5 atoms of iron and 0.34 atom of molybdenum per mol of enzyme. The presence of molybdopterin cofactor in dimethyl sulfoxide reductase was identified by reconstitution of cofactor-deficient NADPH nitrate reductase activity from Neurospora crassa nit-I mutant and by UV absorption and fluorescence emission spectra. The enzyme displayed a very broad substrate specificity, reducing various N-oxide and sulfoxide compounds as well as chlorate and hydroxylamine.

Rat liver alcohol dehydrogenase of class III. Primary structure, functional consequences and relationships to other alcohol dehydrogenases

The amino acid sequence of alcohol dehydrogenase of class III from rat liver (the enzyme ADH-2) has been determined. This type of structure is quite different from those of both the class I and the class II alcohol dehydrogenases. The rat class III structure differs from the rat and human class I structures by 133-138 residues (exact value depending on species and isozyme type); and from that of human class II by 132 residues. In contrast, the rat/human species difference within the class III enzymes is only 21 residues. The protein was carboxymethylated with iodo[2(14)C]acetate, and cleaved with CNBr and proteolytic enzymes. Peptides purified by exclusion chromatography and reverse-phase high-performance liquid chromatography were analyzed by degradation with a gas-phase sequencer and with the manual 4-N,N-dimethylaminoazobenzene-4'-isothiocyanate double-coupling method. The protein chain has 373 residues with a blocked N terminus. No evidence was obtained for heterogeneity. The rat ADH-2 enzyme of class III contains an insertion of Cys at position 60 in relation to the class I enzymes, while the latter alcohol dehydrogenase in rat (ADH-3) has another Cys insertion (at position 111) relative to ADH-2. The structure deduced explains the characteristic differences of the class III alcohol dehydrogenase in relation to the other classes of alcohol dehydrogenase, including a high absorbance, an anodic electrophoretic mobility and special kinetic properties. The main amino acid substitutions are found in the catalytic domain and in the subunit interacting segments of the coenzyme-binding domain, the latter explaining the lack of hybrid dimers between subunits of different classes. Several substitutions provide an enlarged and more hydrophilic substrate-binding pocket, which appears compatible with a higher water content in the pocket and hence could possibly explain the higher Km for all substrates as compared with the corresponding values for the class I enzymes. Finally the class III structure supports evolutionary relationships suggesting that the three classes constitute clearly separate enzymes within the group of mammalian zinc-containing alcohol dehydrogenases.

NAD(P)+-independent aldehyde dehydrogenase from Pseudomonas testosteroni. A novel type of molybdenum-containing hydroxylase

Aldehyde dehydrogenase from Pseudomonas testosteroni was purified to homogeneity. The enzyme has a pH optimum of 8.2, uses a wide range of aldehydes as substrates and cationic dyes (Wurster's blue, phenazine methosulphate and thionine), but not anionic dyes (ferricyanide and 2.6-dichloroindophenol), NAD(P)+ or O2, as electron acceptors. Haem c and pyrroloquinoline quinone appeared to be absent but the common cofactors of molybdenum hydroxylases were present. Xanthine was not a substrate and allopurinol was not an inhibitor. Alcohols were inhibitors only when turnover of the enzyme occurred in aldehyde conversion. The enzyme has a relative molecular mass of 186,000, consists of two subunits of equal size (Mr 92,000), and 1 enzyme molecule contains 1 FAD, 1 molybdopterin cofactor, 4 Fe and 4 S. It is a novel type of NAD(P)+-independent aldehyde dehydrogenase since its catalytic and physicochemical properties are quite different from those reported for already known aldehyde-converting enzymes like haemoprotein aldehyde dehydrogenase (EC 1.2.99.3), quino-protein alcohol dehydrogenases (EC 1.1.99.8) and molybdenum hydroxylases.

Detection of the cofactor pyrroloquinoline quinone

In order to demonstrate the presence or absence of a pyrroloquinoline quinone (PQQ) synthesizing capacity in microorganisms, we have found that media and equipment must be treated to remove contaminating PQQ. Procedures are described which appear to be effective for that purpose. These have been used with Acinetobacter calcoaceticus PQQ- strains to develop a sensitive and reliable assay for PQQ. They also have been used to show that under our conditions of growth Escherichia coli does not synthesize PQQ. Fluorescence spectroscopy is not selective enough to detect PQQ in a protein hydrolysate due to background fluorescence in the same spectral regions as PQQ. In addition, PQQ reacts with amino acids to give products that cannot be detected by either fluorescence spectroscopy or biological assay. In this regard, claims that several materials originating from plants or animals contain PQQ should be reexamined. Moreover, PQQ cannot be detected with these methods in hydrolysates of enzymes containing covalently bound PQQ.

Purification and characterization of quinoprotein glucose dehydrogenase from Acinetobacter calcoaceticus L.M.D. 79.41

Quinoprotein glucose dehydrogenase (EC 1.1.99.17) from Acinetobacter calcoaceticus L.M.D. 79.41 was purified to homogeneity. It is a basic protein with an isoelectric point of 9.5 and an Mr of 94,000. Denaturation yields two molecules of PQQ/molecule and a protein with an Mr of 48000, indicating that the enzyme consists of two subunits, which are probably identical because even numbers of aromatic amino acids were found. The oxidized enzyme form has an absorption maximum at 350 nm, and the reduced form, obtained after the addition of glucose, at 338 nm. Since double-reciprocal plots of initial reaction rates with various concentrations of glucose or electron acceptor show parallel lines, and substrate inhibition is observed for glucose as well as for electron acceptor at high concentrations, a ping-pong kinetic behaviour with the two reactants exists. From the plots, Km values for glucose and Wurster's Blue of 22 mM and 0.78 mM respectively, and a Vmax. of 7.730 mumol of glucose oxidized/min per mg of protein were derived. The enzyme shows a broad substrate specificity for aldose sugars. Cationic electron acceptors are active in the assay, anionic acceptors are not. A pH optimum of 9.0 was found with Wurster's Blue and 6.0 with 2,6-dichlorophenol-indophenol. Two types of quinoprotein glucose dehydrogenases seem to exist: type I enzymes are acidic proteins from which PQQ can be removed by dialysis against EDTA-containing buffers (examples are found in Escherichia coli, Klebsiella aerogenes and Pseudomonas sp.); type II enzymes are basic proteins from which PQQ is not removed by dialysis against EDTA-containing buffers (examples are found in A. calcoaceticus and Gluconobacter oxydans).

The gamma 1 and gamma 2 subunits of human liver alcohol dehydrogenase. cDNA structures, two amino acid replacements, and compatibility with changes in the enzymatic properties

cDNA clones corresponding to two alleles of the ADH3 locus were identified by hybridization with synthetic oligodeoxyribonucleotides specific for class I human liver alcohol dehydrogenase. Sequences were determined for a 1457-nucleotide cDNA, covering the whole gamma 2-coding region, and a 1224-nucleotide cDNA, including the region coding for amino acid residues 53-374 of the gamma 1 subunit. Two amino acid replacements between the gamma 1 and gamma 2 subunits were identified. At position 349, isoleucine in gamma 1 instead of valine in gamma 2 is a conservative exchange of a superficial residue which has been ascribed no special importance. The other exchange, at position 271, arginine in gamma 1 and glutamine in gamma 2, explains differences in enzyme properties. Electrophoretically, it is consistent with the less cathodic mobility of the gamma 2 subunit. Functionally, the location of the exchange at the surface of the coenzyme-binding pocket may influence the dissociation of the reduced coenzyme.