allosteric enzymes

Allosteric enzyme

Regulate the flux of bio chemicals through metabolic pathways

Allosteric enzymes catalyze

Committed steps of biochemical pathways

Committed steps

Irreversible under cellular conditions meaning it has a large -ve delta G

Allosteric enzymes consist of

More than one subunit (quaternary and more than one active site)

What kind of molecules can be bound to Allosteric enzymes

Inhibitory and stimulatory

Inhibitors

Bind to regulatory sites on the enzyme which decreases the enzyme activity signalling that there is enough product and turning the pathway off

Stimulation (feed forward)

A metabolite/intermediate produced early in the pathway binds to a regulatory site on an Allosteric enzyme down stream in the metabolic pathway signalling an increase in substrate and increasing enzyme activity

So Allosteric enzymes follow Michaelis menten

No

What kind of kinetics do Allosteric enzymes display

Sigmoidal

R form

Catalyzes reaction

T form

Less active but more stable and common

R and T in converted model

Are in equilibrium but shifted more towards T

Allosteric constant

T/R = Lo typically in the hundreds

Symmetry rule in concerted model

All active sites must be in same state

Concerted model

When [S] is low most enzymes are in stable tense form. As [S] increases it binds to an active site on R trapping all other active sites in R form. As more active sites are in R form it’s easier for substrate to bind

The binding of one substrate to an active site shifts (concerted)

The TR equilibrium shifts toward R

The behaviour of shifting the TR equilibrium is called (concerted)

Cooperativity

Threshold effect

Allosteric enzymes are more sensitive to changes in [S] near Km than Michaelis menten enzymes with the same Vmax

How do regulatory molecules modulate the activity of Allosteric enzymes

Binding to a specific f if sites (Allosteric sites) on the enzyme and inducing conformational change affecting the enzymes activity. CTP: -ve regulator (T state) ATP: +ve regulator (R state)

Heterotrophic effects

How binding of a regulatory (inhibitory or stimulatory) affects Allosteric enzyme activity

How does heterotrophic effects affect kinetic curve

Shift to the left for an activator and to the right for an inhibitor

Homotrophic effects

How binding of substrate effects Allosteric enzyme activity

Sequential model

Binding of substrate to one active site influences the substrate binding to neighbouring active sites