Talk:Metalloproteinase

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[edit] Older class of proteinases

The metallo proteinases The metallo proteinases may be one of the older classes of proteinases and are found in bacteria, fungi as well as in higher organisms. They differ widely in their sequences and their structures but the great majority of enzymes contain a zinc atom which is catalytically active. In some cases, zinc may be replaced by another metal such as cobalt or nickel without loss of the activity. Bacterial thermolysin has been well characterized and its crystallographic structure indicates that zinc is bound by two histidines and one glutamic acid. Many enzymes contain the sequence HEXXH, which provides two histidine ligands for the zinc whereas the third ligand is either a glutamic acid (thermolysin, neprilysin, alanyl aminopeptidase) or a histidine (astacin). Other families exhibit a distinct mode of binding of the Zn atom. The catalytic mechanism leads to the formation of a non covalent tetrahedral intermediate after the attack of a zinc-bound water molecule on the carbonyl group of the scissile bond. This intermediate is further decomposed by transfer of the glutamic acid proton to the leaving group.

[edit] Contradiction ?

I see what I believe is a contradiction in this entry. The sentence "Metalloproteinases bind a metal ion such as Zn²⁺ or Ca²⁺ in their active site" contradicts the sentence "The proper functioning of MMPs involves the binding of Ca and Zn ions as well, but only the latter is bound in the active site of the enzyme, while Ca is only required for maintaining the molecule's conformation", I believe. I would not want to make a change without doing a little research, but if anyone else is confident of the right fix, that will relieve me of the task. -- Ben Best 04:43, 22 January 2007 (UTC)