Procarboxypeptidase, cobalt

Zymogens have been considered to be inactive precursors of enzymes and the activation process to involve the generation of a catalytic or substrate binding site or both 44). Recently, Behnke and Vallee (50) found that the spectral properties of cobalt-substituted procarboxypeptidase A closely resemble those of the cobalt enzyme. Since these spectra were believed to be peculiar to enzymatically active proteins (5i), they investigated the intrinsic catalytic activity of the cobalt zymogen. Remarkably, with certain substrates, cobalt procarboxypeptidase was found to have as much activity, and in some cases even more than the native enzyme. These observations, as well as those of others (52), have questioned the entire concept of zymogens as inactive enzyme precursors. 

Metal binding in procarboxypeptidase A is weaker than in the active enzyme ( 107), Table 7). It was proposed that the bonding involves sulfur and a weaker ligand than N (107). In view of the present concept of the chelating site in carboxypeptidase, further studies of the zymogen are necessary. In that connection, the cobalt complex should be valuable. 

Cobalt has recently been used as an ESR active substitute in zinc metalloenzymes. Whilst liquid helium temperatures may be needed and theoretical aspects of the spectra are not yet as well understood, cobalt has two important advantages over copper as a metal substitute, namely that many cobalt derivatives show some enzymic activity (e.g. cobalt in carbonic anhydrase, alkaline phosphatase and superoxide dismutase) and that g values and hyperfine splitting are more sensitive to ligand environment, particularly when low spin. ESR data have been reported for cobalt substituted thermolysin, carboxypeptidase A, procarboxypeptidase A and alkaline phosphatase [51]. These are all high spin complexes. Cobalt carbonic anhydrase has been prepared and reacted with cyanide [52]. In... 

Replacement of the zinc by cobalt in either bovine procarboxypeptidase or carboxypeptidase resulted in a visible-range CD spectrum, which was inverted and increased in magnitude upon addition in glvcyl-L-tyrosine. Correlations between the optical properties and the catalytic potential of the metalloproteins have been proposed (127). 

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See also in sourсe #XX -- [ ]

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