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Enzymes:
Regulatory
Regulatory enzymes
In a metabolic pathway, which utilizes numerous enzymes, a regulatory
enzyme sets the rate of the overall sequence because it catalyzes the
slowest, rate-limiting reaction
Characteristics of regulatory enzymes
1. Allosteric control
2. Use of binding proteins
3. Reversible covalent modifications
Proteins kinases and phophatases
4. Proteolytic activation
Enzymes:
Regulatory - Allosteric enzyme
Allosteric enzymes
Involve reversible noncovalent binding of regulatory compounds called
allosteric modulators
Binding of modulators can be inhibitory or stimulatory
Binding of modulator causes conformational changes
catalytic
regulatory
Enzymes:
Regulatory - Allosteric enzyme
Aspartate transcarbamoylase (ATCase)
Feedback control by production of end product of pathway
Allosteric inhibition - CTP inhibits aspartate transcarbamoylase by
binding to a regulatory site (not an active site)
Enzymes:
Regulatory - Binding proteins
Trypsin can be bound by trypsin inhibitor (BPTI) and inactivated
Protease inhibitors are common in nature
~10% of blood plasma proteins are protease inhibitors
A mutant of one protease inhibitor causes emphysema
Enzymes:
Regulatory - Reversible covalent modification
Enzymes:
Regulatory - Reversible covalent modification
Methylation - involved in chemotaxis in bacteria
ADP-ribosylation -involved in bacterial nitrogen fixation
Examples: Diphtheria toxin and cholera toxin
D toxin acts on and inhibits EF-2 (protein biosynthesis)
C toxin acts on signaling protein (loss of body fluids - death)
Phosphorylation - 1/3 to 1/2 of all euk. proteins are phosphorylated
Enzymes:
Regulatory - proteolytic activation
Zymogen - inactive precursor (proteases)
many proteases activated this way, activation
is irreversible
Proproteins/proenzymes - inactive precursor (other proteins)
procollagen
blood clotting system