Enzymes – Part II

Biochemistry I

Lecture 2
         2009 (J.S.)



Induced-fit model of enzyme-substrate binding: The enzyme changes shape on substrate binding. The
active site forms a shape complementary to the substrate only after the substrate has been bound.

















































       Irreversible inhibition

    Irreversible inhibitors are usually compounds not of biological origin, which bind onto an
enzyme mostly covalently and make substrate binding impossible.

    Some of them called "active-site directed inhibitors" are used in experimental studies of
enzymes because they permit to map the active sites (affinity labels structurally similar to the
substrate, other group-specific reagents).

    Heavy metal ions bind and inhibit irreversibly enzymes during isolation.

     Mechanism-based inhibitors (suicide inhibitors) are recognized as substrates, initially
processed, but catalysis generates a reactive intermediate that inactivates the enzyme (e.g.
α[1]-antitrypsin, penicillin, aspirin).