ABSTRACT
A recent review [64] lists other enzymes without corrin or porphyrin, which are claimed to be Co-dependent (but see below), as:
1. Methionine aminopeptidase (X-ray structure published [65]) 2. Prolidase or proline dipeptidase 3. Nitrile hydratase (similar to an Fe-dependent analogue; both used indust
tion of D-glucose to D-fructose) 5. Methylmalonyl-CoA carboxytransferase (also contains biotin) 6. Lysine 2 ,3-aminomutase (also contains pyridoxal phosphate and Fe-S clus
ters) 7 . Bromoperoxidase from Pseudomonas putida
In all cases, except perhaps case 3, the apoenzyme may be activated by several different metal ions and claims that Co is essential must be treated with caution. A recent study [66] of the activation of methionine aminopeptidase by variety of diva lent metal ions in the presence and absence of physiological concentrations of glu tathione (GSH) found that Co2+ (unlike Zn2+) was insoluble in the presence of GSH and that the Co-(but not the Zn-) activated enzyme was inactivated by GSH. It was their conclusion that “ given that the in vivo concentration of Zn2+ is at least 1,000fold higher than that of Co2+, and that Co2+ is insoluble in physiological concentra tions of GSH, it is probable that yeast Met aminopeptidase is actually a Zn2+ metalloprotease (and that) ... there are not likely to be any cytoplasmic enzymes that use free Co2+” .
