Biochem Chapter 7~ Coenzymes And Vitamins

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Cofactors

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required by inactive apoenzymes to convert them to active holoenzymes

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Essential Ions

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mostly metal ions and organic compounds known as coenzymes

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Coenzymes

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Act as a group transfer reagents. They are specific for the chemical groups that accept and donate.

-Can carry a hydrogen, an electon, or some other large group.

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Metal Activated Enzymes

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either have an absolute requirement for added metal ions or are stimulated by the addition of metal ions.

Monovalent: K+
Divalent: Ca 2+, Mg 2+

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Metalloenzymes

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contain firmly bound metal ions at their active sites. Most common are transitition metals; iron and zinc, and less often copper and cobalt. In heme groups Fe, Non-heme groups iron is found in metallaenzymes in the form of iron-sulfur clusters

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Iron-sulfur clusters

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[2Fe-2S] and [4Fe-4S]
S- is from cysteine residues
-each group can only accept on electron

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Prosthetic Group

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Remains bound to the enzyme during the course of the reaction. In some cases, the prosthetic group is covalently attached to its apoenzyme, while in other cases it is tightly bound to the active site by many weak interactions. Both cosubstrates and prosthetic groups supply active sites with reactive groups not present on the side chains of amino acid residues

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vitamin-derived coenzymes

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are derivatives of vitamins, which are compounds that cannot be synthesized by mammals and must be obtained as nutrients.