Enzyme complexes phosphorus-containing compounds

Paramagnetic Probes of Enzyme Complexes with Phosphorus-Containing Compounds... 

Careful analysis of the linewidth of the E P complex has indicated that the dissociation of noncovalent phosphate is the rate-Umiting step in the turnover of the enzyme (Hull et al., 1976). A study of the phosphorylated apoenzyme revealed that the linewidth observed was much narrower than that for the metal-containing enzyme. This suggested considerable flexibility for the residue (Chlehowski et al, 1976) in contrast to the holoenzyme, where the observed linewidth has been interpreted as that of a rigidly held moiety (Vogel et al., 1982). pH titrations showed that the residue in the apoenzyme cannot be protonated until the enzyme dissociates and unfolds at low pH (Chlehowski et al., 1976). The phosphorus nucleus in the apo-phosphoryl enzyme is coupled to the methylene protons of the serine with a coupling constant of 13 Hz, indicating that rotomers 1 or 3 are dominant and not much rotomer 2 is present, in contrast to the model compound (see 3, Scheme 3) (Chlehowski et al., 1976). 

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