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Enzyme
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Biological molecules (proteins) that act as catalysts and help complex reactions.
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are specific to their substrates and each enzyme has its own optimum pH
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Substrate
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Material upon which an enzyme acts.
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Enzyme inhibition
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important in normal metabolism for control of pathways.
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Reversible inhibitor
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competitive inhibition
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(Raises Km only) Same size and shape with the substrate
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noncompetitive inhibition
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(Lowers Vmax only) inhibitor doesn't mind whether there is a substrate or not. but when the inhibitor binds, it switches off catalysis.
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uncompetitive inhibition
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(Lowers Vmax and Km) the inhibitor can ONLY be on the surface of the enzyme if the substrate is there.
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Irreversible inhibitor
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acts by reacting with the enzyme protein, usually at the active site(substrate site), to permanently block activity.
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Vmax is the maximum rate of an enzyme catalysed reaction i.e. when the enzyme is saturated by the substrate.
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Km is measure of how easily the enzyme can be saturated by the substrate.
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Km and Vmax are constant for a given temperature and pH and are used to characterise enzymes. They can be used to identify types of inhibitors i.e. competitive, non-competitive and uncompetitive.
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In the case of metal ion cofactors
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Stabilise the structure, not directly involved in the chemistry
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Ca++ with some proteinases
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part of substrate
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Mg++-ATP with some kinases
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part of active site
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Zn++ in alcohol dehydrogenase
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Organic cofactors
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coenzymes
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they do come on and off like other substrates (NAD+)
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prosthetic groups
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a cofactor that forms a permanent part of the enzyme's active site.
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Doesn't come on and off in a catalytic cycle (FAD,PLP)
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Why use coenzyme in one case and not in the other case?
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Metabolic point: NAD is one of a range of cofactor substances that is present in small concentration
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They turn over and over again to process a large amount of substances
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Pathway is to process large amount with tiny amount of coenzyme
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