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J M Pratt

Publications and source records attributed to J M Pratt.

45 records · Page 3Linked to original sources
PubMed1970

The chemistry of vitamin B 12. The co-ordination of biologically important molecules.

The following equilibrium constants (given as logK in units of m(-1)) were determined for the substitution of co-ordinated H(2)O in aquocobalamin by glycine (bound through N) 5.8, cysteine (bound through S) 6.0 or 8.3, depending on the value chosen for the pK of the thiol group, and phenolate 2.9. The spectrum of the phenolate cobalamin shows an additional intense absorption band at 468nm with a molar extinction coefficient of 1.1x10(4), which is assigned to a charge transfer from the phenolate to the cobalt ion. Equilibrium constants have also been determined for the equilibria between adenylcobamide cyanide and CN(-), HO(-) and H(+), which show that the adenine is more easily displaced by CN(-) and HO(-) than is 5,6-dimethylbenziminazole in vitamin B(12), but can be protonated by acid while still remaining co-ordinated to the cobalt. It is shown that in the binding of corrinoids to proteins and polypeptides the formation of hydrogen bonds is far more important than co-ordination by the metal.

Adenine↗
PubMedDate not supplied

Metalloenzymes as molecular switches: the role of conformation changes in controlling activity.

Enzymatically important conformation changes have been classified according to the nature of the trigger (capital S, I, A for substrate, reaction intermediate, allosteric modifier) and the rate of change (subscript f or s, if fast or slow relative to the enzymatic reaction). It is suggested that, in Cu superoxide dismutase, the known protonation of the product (to give H2O2) under nonequilibrium conditions involves an essentially irreversible If change.

Electron Transport Complex IV↗