The mechanism of enzyme action.

The important facts are that two histidines are located very close together exactly as we suggested, namely, histidine 12, which probably hydrogen-bonds to the attacking hydroxyl, and histidine 119, which probably hydrogen-bonds to the leaving oxygen

B R Rabin

2007

Scholarcy highlights

  • Available about this enzyme, including the complete If the rate of alkylation of ribonuclease by iodothree-dimensional structure of the protein
  • The deal of chemical and kinetic information which sheds reaction of a simple imidazole with iodoacetic acid light on the mechanism of its catalytic action and it is does not vary withpH in the same way, but follows a possible to suggest tentatively the nature of the simple titration curve inflecting about the pK of the reaction pathway
  • There is obviously an ancillary acid enhancement factors, which are of the order of group required for the reaction of the enzyme with magnitude of 10,10 is still problematical and will not iodoacetic acid
  • The enzyme consists of a single chain of 124 amino emerged that in the enzyme these two histidines acid residues; in general, the molecule is kidney- must be located close together three-dimensionally, shaped containing a depression, and there is good in such a way that one of them in the acid form can reason to believe that the active site is in the depres- promote the reactivity of the other towards alkylatsion
  • Which histidine is alkylated is implicated because, whereas removal of the end would depend amongst other things on the distributhree amino acids from the C-terminus has no effect tion of the charges
  • This general picture would explain on catalytic activity, removal of the one, ie, why either of these two histidines, but never both in aspartate 121, results in complete loss of catalysis. the same molecule, is alkylated by iodoacetic acid
  • The hydrolysis of the cyclic phosphate, where R is H in the illustration, requires the reverse movements of one proton towards histidine 119 and away from histidine 12 to the 2' oxygen; one vibration of the phosphorus in the middle of the trigonal bipyramid will give the second stage of reaction hydrolysis

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