Studies on biotin dependent carboxylases and the properties of carboxybiotin
Biotin dependent carboxyl-transfer reactions have been studied using biotin and pyruvate carboxylases. The pH profile for the Mg/sup 2 +/ and MgATP dependent carboxylation of biotin by bicarbonate shows that an enzymic base with a pK of 6.5 must be unprotonated for catalysis to occur. The pH profiles for the carboxyl-transfer reaction of pyruvate carboxylase have been obtained by studying the decarboxylation of oxalacetate stimulated by the presence of oxamate. Similarly, /sup 13/C and /sup 2/H isotope effects have been measured for the decarboxylation of oxalacetate by both enzymic and nonenzymic means. From these studies the authors can conclude that carboxyl-transfer between biotin and oxalacetate is at least partially rate-limiting and is not concerted with proton-transfer. The lack of any apparent enzymic acid-base catalyst (the V/K profile for oxalacetate is pH independent) suggests that proton transfer may occur directly between biotin and the carbanion formed when oxalacetate is decarboxylated. The pH profile for the nonenzymatic decarboxylation of carboxybiotin shows a plateau below pH 4 (k = 0.012 min/sup -1/ at 2/sup 0/C), and a lower plateau above pH 8 (k = 0.005 min/sup -1/ at 25/sup 0/C). A proton inventory at low pH is linear, while at high pH it is curved. These data suggest that two different mechanisms operate at high and low pH.
- Research Organization:
- Univ. of Wisconsin, Madison
- OSTI ID:
- 5220373
- Report Number(s):
- CONF-8606151-
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Journal Name: Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States) Vol. 45:6; ISSN FEPRA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
AZOLES
BARYONS
BIOCHEMICAL REACTION KINETICS
BIOTIN
CARBON 13
CARBON ISOTOPES
CARBON-CARBON LYASES
CARBOXY-LYASES
CARBOXYLASE
CARBOXYLATION
CARBOXYLIC ACID SALTS
CARBOXYLIC ACIDS
CATALYSIS
CHEMICAL PROPERTIES
CHEMICAL REACTIONS
DECARBOXYLATION
DEUTERIUM
ELEMENTARY PARTICLES
ENZYMES
EVEN-ODD NUCLEI
FERMIONS
HADRONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN ISOTOPES
IMIDAZOLES
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
LYASES
NUCLEI
NUCLEONS
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXALATES
PH VALUE
PROTONS
REACTION KINETICS
STABLE ISOTOPES
VITAMIN B GROUP
VITAMINS