Isotope effect studies of the pyridoxal 5'-phosphate dependent histidine decarboxylase from Morganella morganii

Journal Article · Tue Aug 09 04:00:00 EDT 1988 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00416a016· OSTI ID:6823059

Abell, L M; O'Leary, M H

The pyridoxal 5'-phosphate dependent histidine decarboxylase from Morganella morganii shows a nitrogen isotope effect k/sup 14//k/sup 15/ = 0.9770 +/- 0.0021, a carbon isotope effect k/sup 12//k/sup 13/ = 1.0308 +/- 0.0006, and a carbon isotope effect for L-(..cap alpha..-/sup 2/H)histidine of 1.0333 +/- 0.0001 at pH 6.3, 37/sup 0/C. These results indicate that the overall decarboxylation rate is limited jointly by the rate of Schiff base interchange and by the rate of decarboxylation. Although the observed isotope effects are quite different from those for the analogous glutamate decarboxylase from Escherichia coli, the intrinsic isotope effects for the two enzymes are essentially the same. The difference in observed isotope effects occurs because of a roughly twofold difference in the partitioning of the pyridoxal 5'-phosphate-substrate Schiff base between decarboxylation and Schiff base interchange. The observed nitrogen isotope effect requires that the imine nitrogen in this Schiff base is protonated. Comparison of carbon isotope effects for deuteriated and undeuteriated substrates reveals that the deuterium isotope effect on the decarboxylation step is about 1.20; thus, in the transition state for the decarboxylation step, the carbon-carbon bond is about two-thirds broken.

• Research Organization: Univ. of Wisconsin, Madison (USA)
• OSTI ID: 6823059
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:16; ISSN BICHA
• Country of Publication: United States
• Language: English

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63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ALDEHYDES
AMINO ACIDS
AZINES
AZOLES
BACTERIA
CARBON 12
CARBON 13
CARBON ISOTOPES
CARBON-CARBON LYASES
CARBOXY-LYASES
CARBOXYLIC ACIDS
DECARBOXYLASES
DEUTERIUM COMPOUNDS
ENZYMES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HISTIDINE
HYDROGEN COMPOUNDS
IMIDAZOLES
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
LYASES
MICROORGANISMS
NITROGEN 14
NITROGEN 15
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PYRIDINES
PYRIDOXAL
STABLE ISOTOPES