Stereochemistry of the reactions of glutamate-1-semialdehyde aminomutase with 4,5-diaminovalerate.
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 (lambdamax = 420 nm) was deduced to be the protonated external aldimine with the 4-amino group. The intermediate formed with d-DAVA (lambdamax = 390 nm) was deduced to be the unprotonated external aldimine with the 5-amino group.
D'Aguanno
Simona
S
Dipartimento di Scienze Biochimiche "A Rossi Fanelli," Università degli Studi di Roma "La Sapienza," Rome, Italy.
Gonzales
Isabel Nogues
IN
Simmaco
Maurizio
M
Contestabile
Roberto
R
John
Robert A
RA
D000447:Aldehydes / Q000737:chemistry; D000599:Amino Acids, Diamino / Q000737:chemistry*; D000622:Aminolevulinic Acid / Q000737:chemistry; D002208:Caproates / Q000737:chemistry; D018698:Glutamic Acid / Q000737:chemistry; D019751:Intramolecular Transferases / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D013237:Stereoisomerism; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000737:chemistry
D000447:Aldehydes; D000599:Amino Acids, Diamino; D002208:Caproates; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D000622:Aminolevulinic Acid; C074874:4,5-diaminopentanoic acid; D019751:Intramolecular Transferases; C061049:glutamate-1-semialdehyde 2,1-aminomutase