Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis.

Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis. Research Abstract Details 

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Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis. Abstract Text:

Tracy D Turbeville,Junshun Zhang,Gregory A Hunter,Gloria C Ferreira,

5-Aminolevulinate synthase (ALAS), the first enzyme of the heme biosynthetic pathway in mammalian cells, is a member of the alpha-oxoamine synthase family of pyridoxal 5'-phosphate (PLP)-dependent enzymes. In all structures of the enzymes of the -oxoamine synthase family, a conserved histidine hydrogen bonds with the phenolic oxygen of the PLP cofactor and may be significant for substrate binding, PLP positioning, and maintenance of the pKa of the imine nitrogen. In ALAS, replacing the equivalent histidine, H282, with alanine reduces the catalytic efficiency for glycine 450-fold and decreases the slow phase rate for glycine binding by 85%. The distribution of the absorbing 420 and 330 nm species was altered with an A420/A330 ratio increased from 0.45 to 1.05. This shift in species distribution was mirrored in the cofactor fluorescence and 300-500 nm circular dichroic spectra and likely reflects variation in the tautomer distribution of the holoenzyme. The 300-500 nm circular dichroism spectra of ALAS and H282A diverged in the presence of either glycine or aminolevulinate, indicating that the reorientation of the PLP cofactor upon external aldimine formation is impeded in H282A. Alterations were also observed in the K(Gly)d value and spectroscopic and kinetic properties, while the K(PLP)d increased 9-fold. Altogether, the results imply that H282 coordinates the movement of the pyridine ring with the reorganization of the active site hydrogen bond network and acts as a hydrogen bond donor to the phenolic oxygen to maintain the protonated Schiff base and enhance the electron sink function of the PLP cofactor.

Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis. Publishing Authors By Initials

TD Turbeville,J Zhang,GA Hunter,GC Ferreira,

For similar biochemical phenomena, metabolism, and nutrition: biochemical phenomena: substrate specificity research abstracts see: biochemical phenomena, metabolism, and nutrition: biochemical phenomena: substrate specificity research

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Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis. Journal Published:

PUBLICATION TYPE: Research Support, N.I.H., Extr

Journal: Biochemistry

VOLUME: 46

Page Numbers: 5972-81

Journal Abbreviation: Biochemistry

ISSN: 0006-2960

DAY: 1

MONTH: 05

YEAR: 2007

Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis. Information

Number of References:

LANGUAGE: eng

NlmUniqueID: 370623

Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis. Keywords Mesh Terms:

KEYWORDS: Substrate Specificity

MESH TERMS: genetics

Chemical & Substance for Abstract: Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis. Information

Substance Name: 5-Aminolevulinate Synthetase

Registry Number: EC 2.3.1.37

Grant and Affiliation Information for Histidine 282 in 5-aminolevulinate synthase affects substrate binding and catalysis.

AFFILIATION: Department of Molecular Medicine, College of Medicine, University of South Florida, Tampa, Florida 33612, USA.

Country: United States

AGENCY: United States NIDDK

GRANT: DK63191

ACRONYM: DK

MEDLINETA: Biochemistry

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