Nucleophilic Addition and Amide Bond Fission in Creatinase

1 Nucleophilic Addition and Amide Bond Fission in Creatinase 

The first example describes the attack of a nucleophile on a carbonyl-type carbon atom. This reaction is the first step in the creatinase catalyzed cleavage of the amide bond of creatine, which eventually leads to the products urea and sarcosine [79]. 

Natural substrate (guanidinium) and inhibitors (carbamoyl) differ by the presence or absence of a positive charge on this part of the molecule. Thus, addition of water (as OH ) to the carbamoyl moiety and hydrolysis of the inhibitor would result in the development of charge rather than in its dispersal (as for the natural substrate ) in the partially hydrophobic environment of the active site. This explains why carbamoyl sarcosine acts as inhibitor for creatinase. In succinamic acid, the central NCH3 is replaced by CH2 and the proton transfer reaction (step 3) cannot occur. 

Detailed information about the electron distribution in molecules is available from ab initio calculations or from very accurate X-ray diffraction experiments. In the latter case, the results are influenced by the surrounding crystal field. To achieve quantitative agreement between ab initio calculations and diffraction experiments, the influence of the nearest neighbors of the molecule in the crystal field has to be incorpo- 

C-O bond, and similar effects may be expected for C-N bonds with double-bond character, as in the guanidinium group of creatine. 

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