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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.
2.
3.
4.
Enzymes:
Regulatory
Allosteric enzymes
Involve reversible noncovalent binding of regulatory compounds called
allosteric modulators
Binding of modulators can be ___________ or ___________
Binding of modulator causes ____________________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