Ii

Maleic acid carries the hydrogen atoms added to (or removed from) the substrate by many enzymes. Metal ions are also common. Zinc ions are found at the active site of most enzymes that synthesize or degrade nucleic acids. The Zn2+ binds to the negatively charged phosphate groups and weakens the critical bonds.

Enzymes Have Varying Specificities

Some enzymes are extremely specific and will use only a single substrate. Aspartase catalyzes the inter-conversion of aspartic acid and fumaric acid (Fig 7.30). Aspartase will use only aspartate (not similar amino acids such as glutamate) and it uses only the

FIGURE 7.31 Active Site Specificity of Proteases

A) In general, a side chain of an amino acid fits into the pocket of a protease and a clipping mechanism nearby breaks the amino acid chain. B) The pockets have different properties in different protease enzymes. A negative charged pocket as in trypsin binds positively charged residues such as arginine. The hydrophobic pocket of chymotrypsin attracts hydrophobic residues and the shallow pocket of elastase only fits small residues such as glycine or alanine.

A) General mechanism

Substrate cut here

Side chain fits pocket

Protease

Protein substrate

Substrate cut here

Protein substrate

Side chain

Pocket determines specificity

Side chain

Pocket determines specificity

B) Specific active sites

Lys or

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