Enzymes: Regulatorychemistry.creighton.edu/~jksoukup/lec10.pdf · Enzymes: Regulatory Regulatory...
Transcript of Enzymes: Regulatorychemistry.creighton.edu/~jksoukup/lec10.pdf · Enzymes: Regulatory Regulatory...
Enzymes:Regulatory
Regulatory enzymesIn a metabolic pathway, which utilizes numerous enzymes, a regulatoryenzyme sets the rate of the overall sequence because it catalyzes theslowest, rate-limiting reaction
Characteristics of regulatory enzymesAllosteric controlUse of binding proteinsReversible covalent modifications
Proteins kinases and phophatasesProteolytic activation
Enzymes:Regulatory
Allosteric enzymesInvolve reversible noncovalent binding of regulatory compounds calledallosteric modulators
Binding of modulators can be inhibitory or stimulatoryBinding 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 bybinding 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 inhibitorsA 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
Proproteins/proenzymes - inactive precursor (other proteins)procollagenblood clotting system
Zymogen - inactive precursor (proteases)many proteases activated this way, activationis irreversible