Paramagnetic carbon-13 NMR relaxation studies on the kinetics and mechanism of the HCO/sub 3//sup -//CO/sub 2/ exchange catalyzed by manganese(II) human carbonic anhydrase I

Journal Article · Tue Jan 13 04:00:00 EST 1987 · Biochemistry; (United States)

OSTI ID:6616620

Led, J J; Neesgaard, E

A detailed analysis of the stability and activity of Mn(II) human carbonic anhydrase I and the kinetics and mechanism of its catalysis of the HCO/sub 3//sup -//CO/sub 2/ exchange have been performed at pH 8.5. The analysis was based on the paramagnetic relaxation rates R/sub 1p/ and R/sub 2p/ of the /sup 13/C atom of HCO/sub 3//sup -/ in the Mn/sup 2 +//apoenzyme/HCO/sub 3//sup -//CO/sub 2/ system and the HCO/sub 3//sup -/ in equilibrium CO/sub 2/ interconversion rate obtained by the magnetization-transfer technique. The R/sub 1p/ and R/sub 2p/ rates were measured as functions of the temperature, magnetic field strength, and substrate and apoenzyme concentrations and were interpreted on the basis of Solomon-Bloembergen-Morgan theories and general equations for the liquid exchange. From the analysis of the data, a formation constant for the Mn(II) enzyme of log K/sub MA//sup M/ = 5.8 +/- 0.4 was obtained while the activity of the Mn(II) enzyme, measured as the HCO/sub 3//sup -//CO/sub 2/ interconversion rate at (HCO/sub 3//sup -/) = 0.100 M and pH 8.5, was found to be about 4% of that of the native Zn(II) enzyme. Most conspicuously, the resulting distance of only 2.71 +/- 0.03 A between the Mn/sup 2 +/ ion of the enzyme and the /sup 13/C atom of HCO/sub 3//sup -/ in the enzyme-bicarbonate complex indicates that the bicarbonate is bound to the metal ion by two of its oxygen atoms in the central catalytic step, thereby supporting the modified Zn(II)-OH mechanism. In contrast, this binding mode differs from the structure of the complexes suggested in the rapid-equilibrium kinetic model.

• Research Organization: Univ. of Copenhagen, Denmark
• OSTI ID: 6616620
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:1; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
ACID CARBONATES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BODY FLUIDS
CARBON 13
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON ISOTOPES
CARBON OXIDES
CATALYSIS
CHALCOGENIDES
CHROMATOGRAPHY
ENZYME ACTIVITY
ENZYMES
ERYTHROCYTES
EVEN-ODD NUCLEI
ION EXCHANGE CHROMATOGRAPHY
ISOTOPES
KINETICS
LIGHT NUCLEI
LYASES
MAGNETIC RESONANCE
MANGANESE COMPOUNDS
MANGANESE SULFATES
MATERIALS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
OXIDES
OXYGEN COMPOUNDS
PH VALUE
REACTION KINETICS
RELAXATION TIME
RESONANCE
SEPARATION PROCESSES
STABLE ISOTOPES
SULFATES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS