Stereochemistry of the Reactions of Glutamate-1-semialdehyde Aminomutase with 4,5-Diaminovalerate

• Published in: The Journal of biological chemistry Vol. 278; no. 42; pp. 40521 - 40526
• Main Authors: D'Aguanno, Simona, Gonzales, Isabel Nogues, Simmaco, Maurizio, Contestabile, Roberto, John, Robert A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 17.10.2003; American Society for Biochemistry and Molecular Biology
• Subjects: Aldehydes - chemistry; Amino Acids, Diamino - chemistry; Aminolevulinic Acid - chemistry; Caproates - chemistry; gamma-Aminobutyric Acid - chemistry; Glutamic Acid - chemistry; Intramolecular Transferases - chemistry; Intramolecular Transferases - metabolism; Kinetics; Models, Chemical; Stereoisomerism; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M306223200

Conversion of glutamate 1-semialdehyde to the tetrapyrrole precursor, 5-aminolevulinate, takes place in an aminomutase-catalyzed reaction involving transformations at both the non-chiral C5 and the chiral C4 of the intermediate 4,5-diaminovalerate. Presented with racemic diaminovalerate and an excess of succinic semialdehyde, the enzyme catalyzes a transamination in which only the l-enantiomer is consumed. Simultaneously, equimolar 4-aminobutyrate and aminolevulinate are formed. The enzyme is also shown to transaminate aminolevulinate and 4-aminohexenoate to l-diaminovalerate as the exclusive amino product. The interaction of the enzyme with pure d- and l-enantiomers of diaminovalerate prepared by these reactions is described. Transamination of l-diaminovalerate yielded aminolevulinate quantitatively showing that reaction at the C5 amine does not occur significantly. A much slower transamination reaction was catalyzed with d-diaminovalerate as substrate. One product of this reaction, 4-aminobutyrate, was formed in the amount equal to that of the diaminovalerate consumed. Glutamate semialdehyde was deduced to be the other primary product and was also measured in significant amounts when a high concentration of the enzyme in its pyridoxal form was reacted with d-diaminovalerate in a single turnover. Single turnover reactions showed that both enantiomers of diaminovalerate converted the enzyme from its 420-nm absorbing pyridoxaldimine form to the 330-nm absorbing pyridoxamine via rapidly formed intermediates with different absorption spectra. The intermediate formed with l-DAVA (λmax = 420 nm) was deduced to be the protonated external aldimine with the 4-amino group. The intermediate formed with d-DAVA (λmax = 390 nm) was deduced to be the unprotonated external aldimine with the 5-amino group.