Observations on the Organometallic Bond of the Corrinoid Coenzymes

Hogenkamp, Harry P. C.; Rush, James E.; Swenson, Charles A.

doi:10.1016/s0021-9258(18)97192-9

Cited by 98 publications

(47 citation statements)

References 8 publications

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“…Photolyses of Co(III) alkylcobalamins are well-studied reactions where the primary photoproducts are known to be Co(II) and an alkyl radical (Hogenkamp, 1965;Pratt & Whitear, 1971;Taylor et al, 1973;, 1993. In the presence of oxygen, the five-coordinate Co(II) species is quickly oxidized to Co(III) and a water ligand binds to cobalt, forming aquocobalamin.…”

Section: Resultsmentioning

confidence: 99%

Human cobalophilin: The structure of bound methylcobalamin and a functional role in protecting methylcobalamin from photolysis

Frisbie¹,

Chance²

1993

Biochemistry

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The interactions of methylcobalamin with cobalophilin from human serum were analyzed using extended X-ray absorption fine structure (EXAFS) spectroscopy, photolysis of the cobalt-carbon bond of methylcobalamin, and a pKa determination of the protonation of the coordinated nitrogen of 5,6-dimethylbenzimidazole (DMB). These results are consistent with the idea that the DMB nitrogen is still coordinated when protein is bound; however, the ability of a methyl radical (generated by photolysis) to escape the geminate cage of the protein is considerably reduced. For methylcobalamin in solution, the DMB nitrogen ligand is at a distance of 2.20 +/- 0.03 A from cobalt [Sagi, I., & Chance, M. R. (1992) J. Am. Chem. Soc. 114, 8061-8066]. This distance to the lower axial ligand does not change when protein binds (2.20 +/- 0.04 A), nor do the optical spectra exhibit any base-off character. The average of the distance from cobalt to the four equatorial nitrogens of the corrin plane is also unchanged. The pKa for the conversion of the "base-on" to the "base-off" form of methylcobalamin, where the above DMB nitrogen becomes protonated and the Co-N axial bond is cleaved, does not deviate from the free cobalamin value of 2.7 when methylcobalamin is bound to cobalophilin. These results indicate that replacement of the DMB ligand with a ligand from the protein is unlikely. Although the background-subtracted EXAFS data sets for free methylcobalamin and for the protein complex are extremely similar, more accurate data with explicit higher shell analysis would be required to entirely rule out ligand replacement. The chemical and electronic nature of the ligand changes little.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Resultsmentioning

confidence: 99%

Human cobalophilin: The structure of bound methylcobalamin and a functional role in protecting methylcobalamin from photolysis

Frisbie¹,

Chance²

1993

Biochemistry

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“…This reaction has therefore been investigated by a number of researchers, 5,[7][8][9][10][11][12] especially since the reaction between cyanide and cobalamins provides a convenient means for studying factors that control the rate of heterolytic cleavage of the Co-C bond, such as the degree of polarization of the Co-C bond electron density toward the C atom. 10 There are discrepancies in the literature as to the mechanism of cyanation. In the most recent study, the authors claim that two reactions are kinetically observable (k obs(1) ) 2.9 × 10 -2 s -1 , k obs(2) ) 8.4 × 10 -4 s -1 , 0.1 M KCN, pH 10.5, 0.1 M buffer (NaHCO 3 ), 25 °C) and propose the following reaction mechanism.…”

Section: Introductionmentioning

confidence: 99%

Evidence for the Unexpected Associative Displacement of Adenosyl by Cyanide in Coenzyme B₁₂

1997

Inorg. Chem.

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The reaction of coenzyme B(12) (adenosylcobalamin) with cyanide has been reinvestigated in detail using spectroscopic and kinetic techniques. It has been shown that this reaction proceeds in one kinetically observable step, contradicting previous findings, with rate-determining attack of the first cyanide (k = (7.4 +/- 0.1) x 10(-3) M(-1) s(-1), 25.0 degrees C, I = 1.0 M (NaClO(4))). The activation parameters were found to be DeltaH() = 53.0 +/- 0.6 kJ mol(-1), DeltaS() = -127 +/- 3 J mol(-1) K(-1) and DeltaV() = -10.0 +/- 0.4 cm(3) mol(-1), suggesting an associative displacement mechanism. It is postulated that attack of the first cyanide occurs at the beta-(5'-deoxy-5'-adenosyl) site rather than at the alpha-dimethylbenzimidazole site.

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“…Materials and Methods. Cyanocobalamin was purchased from Sigma Chemical Co. Other corrinoids were prepared from cyanocobalamin by published procedures: aquocobalamin, Hogenkamp and Rush (1968); diaquocobinamide, alkylcobinamides, Pailes and Hogenkamp (1968); (cyanoaquo)cobinamide,3 Friedrich and Bernhauer (1956); alkylcobalamins, Hogenkamp et al (1965);5'-deoxyadenosylcobalamin, Hogenkamp and Pailes (1968). Other chemicals were obtained from commercial sources.…”

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confidence: 99%

Polarography of cobalamins and cobinamides

Hogenkamp¹,

Holmes²

1970

Biochemistry

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Observations on the Organometallic Bond of the Corrinoid Coenzymes

Cited by 98 publications

References 8 publications

Human cobalophilin: The structure of bound methylcobalamin and a functional role in protecting methylcobalamin from photolysis

Human cobalophilin: The structure of bound methylcobalamin and a functional role in protecting methylcobalamin from photolysis

Evidence for the Unexpected Associative Displacement of Adenosyl by Cyanide in Coenzyme B₁₂

Polarography of cobalamins and cobinamides

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Observations on the Organometallic Bond of the Corrinoid Coenzymes

Cited by 98 publications

References 8 publications

Human cobalophilin: The structure of bound methylcobalamin and a functional role in protecting methylcobalamin from photolysis

Human cobalophilin: The structure of bound methylcobalamin and a functional role in protecting methylcobalamin from photolysis

Evidence for the Unexpected Associative Displacement of Adenosyl by Cyanide in Coenzyme B12

Polarography of cobalamins and cobinamides

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Product

Resources

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Evidence for the Unexpected Associative Displacement of Adenosyl by Cyanide in Coenzyme B₁₂