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M M Palcic

Publications and source records attributed to M M Palcic.

At least 91 records · Page 5Linked to original sources
PubMed1993

Kinetics and stereospecificity of the lysyl oxidase reaction.

The structural specificity of amine oxidation by lysyl oxidase was investigated using kinetic and NMR spectroscopic analyses. Substrate efficiency increased with increasing molecular distance from the alpha-carbon of the aromatic moiety substituted on the aliphatic chains of a series of primary amines. The p-hydroxyl substituent of p-hydroxybenzylamine significantly increased kcat over that of benzylamine, whereas this was not the case when tyramine and phenethylamine were compared. Direct spectrophotometric measurement of p-hydroxybenzaldehyde formation yielded burst kinetics, the second, slower phase of which was eliminated under anaerobic conditions. Thus, enzyme reoxidation is the more rate-limiting of the two half-reactions catalyzed with this substrate by this ping-pong enzyme. 1H NMR spectroscopy of the alcohol reductively derived from the aldehyde product of the lysyl oxidase-catalyzed oxidation of deuterated tyramine indicated that the pro-S but not the pro-R alpha-deuteron was catalytically abstracted. Moreover, lysyl oxidase catalyzed solvent exchange of protons at the C-2 position. Such stereospecificity and proton exchange uniquely differentiates lysyl oxidase from all but an aortic semicarbazide-sensitive amine oxidase among the pro-S-specific copper-dependent amine oxidases analyzed thus far.

Amines↗
PubMed1993

Use of the "core-2"-N-acetylglucosaminyltransferase in the chemical-enzymatic synthesis of a sialyl-LeX-containing hexasaccharide found on O-linked glycoproteins.

A simple preparation of the "core-II" N-acetylglucosaminyltransferase (UDP-D-GlcpNAc:beta-D-Galp-(1-->3)-alpha-D-GalpNAc (GlcNAc to GalNAc) beta-(1-->6)-GlcNAc-transferase, GlcNAcT, EC 2.4.1.102) from commercial mouse kidney acetone powder is reported. The enzyme obtained in a single step of affinity chromatography is suitable for use in preparative oligosaccharide synthesis. In conjunction with previously described preparations of beta-(1-->4)-galactosyltransferase (EC 2.4.1.22), alpha-(2-->3)-sialytransferase (EC 2.4.99.6) and alpha-(1-->3/4)-fucosyltransferase (EC 2.4.1.65), the GlcNAcT was used in the first step of a sequence which converted the disaccharide beta-D-Galp-(1-->3)-alpha-D-GalpNAc-OR into the sialyl-LeX-containing structure alpha-D-NeupAc-(2-->3)-beta-D-Galp- (1-->4)-[alpha-L-Fucp-(1-->3)]-beta-D-GlcpNAc-(1-->6)-[beta-D-Galp - (1-->3)]-alpha-D-GalpNAc-OR (5), where R = (CH2)8CO2Me. Hexasaccharide 5, thus assembled in only one week once the enzymes were prepared, was characterized by 1H and 13C NMR spectroscopy and fast-atom bombardment mass spectrometry, as were all intermediate oligosaccharides. The core II GlcNAcT thus joins the expanding repertoire of readily available reagents for the rapid assembly of oligosaccharides.

Animals↗
PubMed1993

Acceptor-substrate recognition by N-acetylglucosaminyltransferase-V: critical role of the 4"-hydroxyl group in beta-D-GlcpNAc-(1-->2)-alpha-D-Manp(1-->6)-beta-D-Glcp-OR.

The enzyme N-acetylglucosaminyltransferase-V (GlcNAcT-V) transfers GlcNAc from UDP-GlcNAc to the OH-6' group of oligosaccharides terminating in the sequence beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->6)-beta-D-Glcp (or Manp)-OR (5, R = (CH2)7CH3) to yield the sequence beta-D-GlcpNAc-(1-->2)-[beta-D-GlcpNAc-(1-->6)]-alpha-D-Manp-(1--> 6)- beta-D-Glcp (or Manp)-OR. Biosynthetically, if beta-(1-->4)-galactosyltransferase acts first on 5, the product beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->6)-be ta-D-Glcp (or Manp)-OR (7) is no longer a substrate for GlcNAcT-V even though it retains the active OH-6' group. The reason for this loss in activity is examined in this paper. Six analogues of the acceptor trisaccharide 5, all with the reducing-end D-gluco configuration, were chemically synthesized. A key feature of the synthetic scheme is the use of 1,2-diaminoethane for the efficient removal of N-phthalimdo protecting groups. In these analogues OH-4 of the terminal sugar unit, the site of galactosylation by GalT in the normal GlcNAc-terminating trisaccharide 5, was systematically replaced by OMe, F, NH2, NHAc, and H, as well as inverted to the galacto configuration. The interactions of the resulting trisaccharide analogues with GlcNAcT-V from hamster kidney were then evaluated kinetically. All six compounds were found to be essentially inactive either as acceptors or as inhibitors of GlcNAcT-V. The conclusion is reached that galactosylation of natural acceptors for GlcNAcT-V destroys acceptor activity, not by introduction of the steric bulk of an added sugar residue, but by destroying an important hydrogen-bonding interaction of terminal OH-4 of the GlcNAc residues with the enzyme. This OH-4 group is therefore designated as a key polar group for GlcNAcT-V.

Animals↗
PubMed1992

Identification of topaquinone and its consensus sequence in copper amine oxidases.

The nature of the active site cofactor and the amino acid sequence flanking this structure have been determined in a range of copper amine oxidases. For enzymes from porcine plasma, porcine kidney, and pea seedlings, proteolytic digestion was performed on phenylhydrazone or p-nitrophenylhydrazone derivatives. Thermolysin treatment leads to relatively small active site peptides, which have been characterized by Edman degradation and by resonance Raman spectroscopy. Resonance Raman spectra of peptides show identical peak positions and intensities relative to each other and to a model p-nitrophenylhydrazone derivative of topaquinone hydantoin, establishing topaquinone as the cofactor in each instance. Edman degradation of peptides provides active site sequences for comparison to previous determinations with bovine serum and yeast amine oxidases. The available data establish a consensus sequence of Asn, Topa, Asp/Glu. Trypsin leads to significantly longer peptides, which reveal a high degree of sequence identity between plasma proteins from bovine and porcine sources (89%), with significantly decreased identity between the porcine serum and intracellular amine oxidases (56%). A lower degree of identity (45%) is observed between the pea seedling and mammalian enzymes. As an alternative to the isolation of active site peptides for topaquinone identification, visible spectra of intact proteins have been investigated. It is shown that p-nitrophenylhydrazone derivatives of native enzymes, active site-derived peptides, and a topaquinone model exhibit identical behavior, absorbing at 457-463 nm at neutral pH (pH 7.2) and at 575-587 nm in basic solution (1-2 M KOH). These spectral properties, which appear unique to topaquinone, provide a rapid and simple test for the presence of this cofactor in intact enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amine Oxidase (Copper-Containing)↗
PubMed1992

Enzymatic transfer of a preassembled trisaccharide antigen to cell surfaces using a fucosyltransferase.

The Lewis alpha (1-->3/4)-fucosyltransferase (Le-FucT) is known to fucosylate both Type I (beta Gal(1-->3) beta GlcNAc) and Type II (beta Gal(1-->4) beta GlcNAc) sequences even when these are sialylated at OH-3 or fucosylated at OH-2 of the terminal Gal residues. These acceptor sequences are ubiquitous on mammalian cell-surface glycoproteins and glycolipids. The Le-FucT enzyme is therefore a potential candidate as a universal reagent for the modification of cell surfaces. We have found that a readily accessible, partially purified Le-FucT from human milk, which normally uses GDP-fucose (a 6-deoxy sugar) as the donor for the transfer of a single fucose residue, will also transfer a fucose residue substituted on C-6 by a very large sterically demanding structure, in this instance, a synthetic blood group antigen. As a demonstration of the ability of the Le-FucT to modify glycoconjugates in a mild and specific manner, we chemically synthesized the complex sugar-nucleotide alpha Gal(1-->3) [alpha Fuc(1-->2)]-beta Gal-O-(CH2)8COHN(6)-beta-L-fucose-GDP (13) which is a GDP-fucose analog where the human blood group B trisaccharide antigen is covalently linked to C-6 of fucose through an amino group. It is shown that, in enzyme-linked immunosorbent assays, the Le-FucT uses both immobilized beta Gal(1-->3) beta GlcNAc-bovine serum albumin conjugates and fetuin as acceptor substrates and renders them blood group B-active as detected by a monoclonal anti-B blood-grouping antibody. The fucose residue to which the B-trisaccharide is linked therefore becomes covalently attached to the acceptor oligosaccharide chains of those glycoproteins. Incubation of type "O" erythrocytes with the Le-FucT and complex donor 13 results in the covalent transfer of alpha Gal(1-->3) [alpha Fuc(1-->2)] beta Gal-O-(CH2)8COHN(6)-beta-L-Fuc to cell-surface acceptors since the cells become phenotypically "B" and are agglutinated by the same antibody. It is proposed that the Le-FucT represents a powerful new tool with the ability to label animal cell surfaces with preassembled oligosaccharide and possibly also other complex recognition markers.

ABO Blood-Group System↗
PubMed1992

An electrophoresis-based assay for glycosyltransferase activity.

Polyacrylamide gel electrophoresis (PAGE) and capillary zone electrophoresis (CZE) were used to measure the activity of glycosyltransferases. Acceptor molecules were prepared by reductive amination of the monopotassium 7-amino-1,3-naphthalenedisulfonic acid (AGA) Schiff base with sugars. The resulting sugar conjugates were purified by gradient PAGE and recovered using semidry electrotransfer into a positively charged nylon membrane. The beta(1----4)galactosyltransferase was shown, by PAGE analysis, to transfer a beta-galactosyl residue to the AGA conjugate of beta-D-GlcNAc-(1----4)-beta-D-GlcNAc-(1----4)-D-GlcNAc (compound 4). Similarly, alpha(1----2)fucosyltransferase isolated from porcine submaxillary glands was shown to transfer fucose from GDP-fucose to the AGA conjugate of beta-D-Gal-(1----4)-beta-D-GlcNAc-(1----6)-D-Gal (compound 5). This conjugate (compound 5) was also an acceptor for the alpha(1----3/4)fucosyltransferase partially purified from human milk. The latter reaction was followed by both gradient PAGE and CZE, having sensitivities of 200 pmol and 80 fmol, respectively.

2-Naphthylamine↗
PubMed1992

Stereochemical course of tyramine oxidation by semicarbazide-sensitive amine oxidase.

Two semicarbazide-sensitive amine oxidases (SSAO's) from bovine and porcine aortic tissue were partially purified and characterized, and the stereochemical course of amine oxidation was evaluated. The porcine and bovine SSAO's were membrane bound glycoproteins, with Km values for benzylamine of 8 and 16 microM, respectively. The reactivity of SSAO with semicarbazide and phenylhydrazine suggests that the cofactor is a carbonyl type molecule. The stereochemical course of the bovine and porcine aortic semicarbazide-sensitive amine oxidase reaction was investigated using chiral tyramines, deuterated at C-1 and C-2, and 1H-NMR spectroscopy to establish the loss or retention of deuterium in product p-hydroxyphenethyl alcohols. The preferred mode of tyramine oxidation was found to occur with the loss of pro-S proton at C-1, coupled with solvent exchange into C-2, a pattern which has not been observed for any copper amine oxidase examined to date. The solvent exchange reaction also occurred stereospecifically, with loss from and reprotonation to the pro-R position, suggesting that these two processes occur from the same face of the enamine double bond.

Amine Oxidase (Copper-Containing)↗
PubMed1992

Enzyme-linked immunosorbent assays for the measurement of blood group A and B glycosyltransferase activities.

ELISA assays have been developed for alpha(1-3)N-acetylgalactosaminyltransferase (blood group A transferase) and alpha(1-3)galactosyltransferase (blood group B transferase) activities. In these assays, microtitre plates coated with the bovine serum albumin conjugate of a synthetic Fuc alpha 1-2Gal beta-R acceptor substrate are incubated with the appropriate nucleotide donor (UDP-GalNAc or UDP-Gal) and human serum as the enzyme source. The resulting trisaccharide products Fuc alpha 1-2(GalNAc alpha 1-3)Gal beta-R-BSA or Fuc alpha 1-2(Gal alpha 1-3)Gal beta-R-BSA are detected and quantified with monoclonal antibodies selected not to cross-react with the substrate structure. With less than a microliter of human serum, product formation is proportional to enzyme concentration and to time of incubation of up to 90 min.

Carbohydrate Sequence↗
PubMed1991

Evaluation of deoxygenated oligosaccharide acceptor analogs as specific inhibitors of glycosyltransferases.

The glycosyltransferases controlling the biosynthesis of cell-surface complex carbohydrates transfer glycosyl residues from sugar nucleotides to specific hydroxyl groups of acceptor oligosaccharides. These enzymes represent prime targets for the design of glycosylation inhibitors with the potential to specifically alter the structures of cell-surface glycoconjugates. With the aim of producing such inhibitors, synthetic oligosaccharide substrates were prepared for eight different glycosyltransferases. The enzymes investigated were: A, alpha(1----2, porcine submaxillary gland); B, alpha(1----3/4, Lewis); C, alpha(1----4, mung bean); D, alpha(1----3, Lex)-fucosyltransferases; E, beta(1----4)-galactosyltransferase; F, beta(1----6)-N-acetylglucosaminyltransferase V; G, beta(1----6)-mucin-N-acetylglucosaminyltransferase ("core-2" transferase); and H, alpha(2----3)-sialyltransferase from rat liver. These enzymes all transfer sugar residues from their respective sugar nucleotides (GDP-Fuc, UDP-Gal, UDP-GlcNAc, and CMP-sialic acid) with inversion of configuration at their anomeric centers. The Km values for their synthetic oligosaccharide acceptors were in the range of 0.036-1.3 mM. For each of these eight enzymes, acceptor analogs were next prepared where the hydroxyl group undergoing glycosylation was chemically removed and replaced by hydrogen. The resulting deoxygenated acceptor analogs can no longer be substrates for the corresponding glycosyltransferases and, if still bound by the enzymes, should act as competitive inhibitors. In only four of the eight cases examined (enzymes A, C, F, and G) did the deoxygenated acceptor analogs inhibit their target enzymes, and their Ki values (all competitive) remained in the general range of the corresponding acceptor Km values. No inhibition was observed for the remaining four enzymes even at high concentrations of deoxygenated acceptor analog. For these latter enzymes it is suggested that the reactive acceptor hydroxyl groups are involved in a critical hydrogen bond donor interaction with a basic group on the enzyme which removes the developing proton during the glycosyl transfer reaction. Such groups are proposed to represent logical targets for irreversible covalent inactivation of this class of enzyme.

Animals↗
PubMed1991

Stereochemical trends in copper amine oxidase reactions.

Copper amine oxidases (EC 1.4.3.6) exhibit atypical stereochemical patterns in the reactions they catalyze. Dopamine and tyramine are oxidized with abstraction of the pro-R hydrogen by the porcine plasma amine oxidase, the pro-S hydrogen by pea seedling amine oxidase and a net nonstereospecific proton abstraction by the bovine plasma enzyme. This provides the first example in which a reaction catalyzed by enzymes in the same formal class occurs by all three possible stereochemical routes. To assess the underlying mechanistic significance of this heterogeneity, we have established the stereochemical course of the oxidation of tyramine by five additional copper amine oxidases using 1H NMR spectroscopy. Reactions catalyzed by rabbit and sheep serum amine oxidases are nonstereospecific. These enzymes exhibit rare mirror image binding with differential flux through two opposite and stereospecific reaction pathways. Differential primary kinetic isotope effects are observed for each mode, 8 and 4.6 for pro-S abstraction and 2.6 and 2.7 for pro-R abstraction by the sheep and rabbit amine oxidases, respectively. Tyramine oxidations catalyzed by the soybean and chick pea amine oxidases and porcine kidney diamine oxidase, however, are all stereospecific, occurring with loss of the pro-S hydrogen at C-1. Solvent exchange profiles are consistent within each stereochemical class of enzyme; the pro-R and nonstereospecific enzymes exchange solvent into C-2 of product aldehydes, the pro-S enzymes do not.

Amine Oxidase (Copper-Containing)↗
PubMed1991

Inhibition of cytoplasmic aspartate aminotransferase from porcine heart by R and S isomers of aminooxysuccinate and hydrazinosuccinate.

D- and L-aminooxysuccinate were synthesized and evaluated as inhibitors of cytoplasmic aspartate aminotransferase (EC 2.6.1.1) from porcine heart. L-Aminooxysuccinate was shown to be a slow binding inhibitor of the pyridoxal phosphate form of the enzyme with a Ki of 160 nM and a half-life of the inhibited complex of 8 min. Kinetic analysis revealed that inhibition followed a two-step mechanism in which the last step was rate-limiting. D-Aminooxysuccinate was not inhibitory up to a concentration of 0.1 mM. These compounds were compared to D- and L-hydrazinosuccinate, which are potent slow binding inhibitors of aspartate aminotransferase with Ki values of 1.5 and 0.5 nM, respectively. Models of all four analogs were built into the active site of the closed form of the enzyme. The energy-minimized conformations of both L-isomers bound to aspartate aminotransferase show better geometry for hydrogen bond and ion pair formation than do the corresponding D-isomers. The aldimine double bond formed by the L-isomers is not coplanar with the pyridoxal phosphate ring in accordance with the spectral properties of the inhibitor complexes that are characterized by broad absorbance bands. This lack of planarity was not evident for the models of D-hydrazinosuccinate and D-aminooxysuccinate.

Animals↗
PubMed1991

Flexibility in the donor substrate specificity of beta 1,4-galactosyltransferase: application in the synthesis of complex carbohydrates.

Biosynthetically, bovine N-acetylglucosamine beta 1,4-galactosyltransferase (GalT) catalyses the transfer of galactosyl residues from UDP-Gal to the 4-position of GlcNAc units, resulting in the production of N-acetyllactosamine sequences. UDP-Glc and UDP-GalNAc were also found to act as donors for this enzyme, allowing the preparation of beta Glc(1----4)-beta GlcNAc and beta GalNAc(1----4) beta GlcNAc terminating structures on the milligram scale. GalT could thus be used to add beta GalNAc to beta GlcNAc(1----2) alpha Man terminating structures, converting them to the beta GalNAc(1----4) beta GlcNAc(1----2) alpha Man sequences found on glycoprotein hormones. GalT did not transfer GlcNAc residues from UDP-GlcNAc, but it could utilize UDP-GlcNH2 as a donor. Synthesis of beta GlcNAc(1----4) beta GlcNAc sequences could therefore be accomplished by transfer of GlcNH2 from its UDP derivative, followed by N-acetylation of the product amino-disaccharide using acetic anhydride in methanol. The products of the enzymatic reactions were characterized by 1H-NMR-spectroscopy and fast-atom bombardment mass spectrometry. This work expands the scope of the combined chemical-enzymatic synthesis of complex carbohydrates, using glycosyltransferases, to the production of oligosaccharides different from those for which these enzymes were designed. These unnatural reactions should find application in glycoprotein and glycolipid remodelling.

Animals↗
PubMed1990

Regulation of N-acetylglucosaminyltransferase V activity. Kinetic comparisons of parental, Rous sarcoma virus-transformed BHK, and L-phytohemagglutinin-resistant BHK cells using synthetic substrates and an inhibitory substrate analog.

Baby hamster kidney (BHK) cells transformed with Rous sarcoma virus, RS-BHK cells, demonstrate a 2.5-fold increase in the activity of N-acetylglucosaminyltransferase V (GlcNAc-T V, EC 2.4.1.155), and this increase in activity appears to be specific for this enzyme. By contrast, a lectin-resistant BHK cell line selected for its ability to grow in high levels of L-phytohemagglutinin, LP3.3, is characterized by a specific decrease in its GlcNAc-T V activity. To test if these alterations in the apparent Vmax of GlcNAc-T V are due to changes in the efficiency of populations of enzymes in RS-BHK and LP3.3 cells compared to the parental BHK cells, we have compared the kinetic properties of the enzymes from these three sources. The Km constants observed for both the sugar nucleotide donor (UDP-GlcNAc) and two synthetic trisaccharide acceptors were indistinguishable. The Vmax values toward three synthetic acceptors were also determined first for the BHK GlcNAc-T V, and they varied by over 5-fold. When these values were measured for the variant and transformed cell enzymes, however, similar 5-fold differences were still observed, although the absolute values for these acceptors were all higher or lower for the RS-BHK and LP3.3 enzymes, respectively. In addition, we have synthesized a deoxygenated analog of the specific GlcNAc-T V acceptor, beta GlcNAc(1,2) alpha Man(1,6) beta ManOR, where the reactive 6'-OH group has been removed, and the resulting trisaccharide was found to be a competitive inhibitor of the enzyme. The Ki for this inhibitor was near 70 microM for the GlcNAc-T V from all three sources. These kinetic comparisons demonstrate that the enzymes from the three cell types have kinetically indistinguishable active sites. These results suggest that the differences in the apparent Vmax values among the cell types are most likely due to alterations in the number of active molecules rather than in the modulation of either their catalytic activities or specificities.

Animals↗
PubMed1990

An enzyme-linked immunosorbent assay for the measurement of Lewis blood-group alpha-(1----4)-fucosyltransferase activity.

An enzyme-linked immunosorbent assay (ELISA) has been developed for the Lewis blood-group associated alpha-(1----4)-fucosyltransferase activity. Microtiter plates coated with the bovine serum albumin conjugate of a synthetic beta-D-Galp-(1----3)-beta-D-GlcpNAc disaccharide are incubated with a fucosyltransferase preparation in the presence of guanosine 5'-diphosphofucose. The resulting immobilized Lewis-a active trisaccharide beta-D-Galp-(1----3)-[alpha-L-Fucp-(1----4)]-beta-D-GlcpNAc is then detected and quantitated using a monoclonal anti-Lewis-a antibody. Product formation detected in this manner is linear with time, proportional to enzyme activity, and reproducibly quantitated in the 50-400 fmol range.

Carbohydrate Sequence↗
PubMed1990

An enzyme-linked immunosorbent assay for N-acetylglucosaminyltransferase-V.

The development of an enzyme-linked immunosorbent assay (ELISA) for uridine 5'-diphospho-N-acetyl-glucosamine: alpha mannoside beta 1----6 N-acetylglucosaminyltransferase (GnT-V) is reported. The assay quantitates the enzymatic conversion of the specific synthetic GnT-V acceptor GlcNAc beta 1----2Man alpha 1----6Man beta-R (5) to the product GlcNAc beta 1----2[GlcNAc-beta 1----6]Man alpha 1----6Man beta-R (6) when these oligosaccharide structures were covalently attached to bovine serum albumin which was then coated on microtiter wells. Conversion of 5 to 6 was detected using a polyclonal antiserum raised against the product 6 and from which antibodies cross-reacting with acceptor 5 had been removed by affinity adsorption. GnT-V activity detected by ELISA was linearly proportional to both enzyme concentration and time under appropriate experimental conditions where 50-300 fmol of product was formed per microtiter well. GnT-V activity could be measured by ELISA in Triton X-100 extracts of hamster kidney acetone powder and in human serum. The twofold increase in GnT-V activity which is known to accompany Rous sarcoma virus transformation of baby hamster kidney cells could also be quantitated using the ELISA.

Animals↗
PubMed1990

Assays for amino acid decarboxylase enzymes using ion-exchange cartridges.

A general radiochemical method for estimating the activity of amino acid decarboxylases is reported. This method utilizes ion-exchange cartridges to separate unreacted radiolabeled amino acid substrates from product amines, which can then readily be quantitated by liquid scintillation counting. The assay is simple, rapid, and more sensitive than standard 14CO2 trapping procedures if uniformly labeled amino acid substrates are utilized. Acidic, basic, and aromatic amino acid decarboxylases can be assayed with the appropriate choice of cation or anion exchangers. The utility of the method is demonstrated for aspartate-alpha-decarboxylase, tyrosine decarboxylase, and lysine decarboxylase where kinetic parameters are comparable to values obtained by standard radiochemical 14CO2 trapping assays.

Amino Acids↗
PubMed1989

Stereochemistry of copper amine oxidase reactions.

The stereochemical course of the oxidation of stereospecifically deuterated dopamine and tyramine, catalyzed by porcine plasma amine oxidase, has been investigated using 1H NMR spectroscopy. The oxidation proceeds with loss of the pro-R hydrogen at C-1. This stereochemistry is in contrast to that observed with the analogous copper containing oxidases isolated from pea seedlings (pro-S) and bovine plasma (nonstereospecific). There is no precedent for these three distinct stereochemical reaction courses to be followed by enzymes in the same class. Mechanistic differences among the three enzymes are evident from the profiles of solvent exchange into reaction products; however, these differences cannot account for the overall differential stereochemical courses observed.

Amine Oxidase (Copper-Containing)↗