Regulation Of Enzyme Activity 1i5x8

In biological systems,regulation of enzyme activities occur at different stages in one or more of the following ways to achieve cellular economy. Allosteric Regulation. Regulation of enzymes by covalent modifications. Induction and supression of enzyme synthesis.

ALLOSTERIC REGULATION.  Enzymes containing other sites beside the active site are known as allosteric enzymes. Composed of multiple subunits. Regulate the committed step early in the pathway. These are regulated by molecules called effectors(modifiers). Negative effectors inhibit the enzyme activity. Possitive effectors increase the enzyme activity. Can effect the Vmax, Km or both.

Homotropic effectors:When substrate itself act as an effector. Function as possitive effectors.

Heterotropic effectors: Effector is different from the substrate. Feed back inhibition Glycolytic enzyme phosphofrucokinase is allosterically inhibited by citrate. A B C D E

REGULATION OF ENZYME BY COVALENT MODIFICATION. Addition or removal of phosphate groups from specific serine , threonine , or tyrosine residues of the enzyme. Phosphorylation by protein kinases and dephosphorylation by phosphoprotein phosphatases.  EXAMPLE: Phosphorylation of Glycogen phosphorylase increases the enzyme activity Phosphorylation of Glycogen synthase decreases the enzyme activity.

INDUCTION AND REPRESSION OF ENZYME SYNTHESIS. Cells can also regulate the amount of enzyme present usually by altering the rate of enzyme synthesis. Rate of synthesis and degradation determine the enzyme quantity.

INDUCTION OF ENZYME SYNTHESIS. In Bacteria Lactose Induction of β Galactosidase In Animals

Enzymes of urea cycle HMG Co A reductase in cholesterol synthesis

REPRESSION OF ENZYME SYNTHESIS In Bacteria Glucose Repression of β galactosidase In Animals . HMG CoA reductase:Induction or stimulation of synthesis=Fed state or insulin effect. Repression of synthesis=Fasting or starvation

Hormone sensitive lipoprotein lipase:

Induction or stimulation=Adrenaline,cortisol,fastin g and stress. Repression=Insulin,fed state

PROENZYMES Inactive enzymes intially secreated as

large molecules,active sites not exposed. Pepsinogen HCl Pepsin Required for the control of the catalytic activity of enzymes so that catalytic activities only occurs when required. Pancreatic enzymes if all the time active=auto digesion of the pancrease Blood clot enzymes only active when blood clot is formed.