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السبت، 13 أبريل 2019

Regulation of Enzyme Activity

Regulation of Enzyme Activity

Regulation of Enzyme Activity

Regulation by modification
Proteolytic cleavage
Covalent modification
Protein-protein interaction
Allosteric regulation
Properties of allosteric enzymes (important)
Sigmoid kinetics (what does Km mean in this case) (important)
Positive and negative modulators (where do they act and how do they modify activity at constant substrate concentration) (most important)

Models of allosteric transitions (important)

Normal metabolic control may be exerted in a variety of ways. Examples are:
1.Proteolytic Cleavage of inactive Proenzymes to active enzymes
Pepsinogen                   pepsin  + small peptide
in gastrointestinal tract for protein digestion
2.Coagulation cascade—a series of proenzymes are converted to active enzymes. The last step is
Fibrinogen                   Fibrin

Covalent Modification as Control

Chemical modification can either increase or decrease activity. Some examples are:
                            Glycogen Synthetase           
            Phosphatase                           Kinase
                                             Phosphorylated Glycogen
Glycogen phosphorylase
Covalent Phosphorylated Glycogen phosphorylase

  Protein-Protein Interaction

Example is activation of Protein Kinase A
R2C2  + 4 cAMP           R2C2(4cAMP)
                           2R(cAMP)2   +  2C (active)
The catalytic unit (C) is able to phosphorylate and modulate the activity of other enzymes

Properties of Allosteric enzymes

Catalyze essentially irreversible reactions; are rate limiting 
Generally contain more than one polypeptide chain 
Do not follow Michaelis-Menten Kinetics 
Are regulated by allosteric activators or inhibitors 
Can be up-regulated by allosteric activators at constant [S] 
Can be down regulated by allosteric inhibitors at constant [S] 
Activators and Inhibitors need not have any structural resemblance to substrate structure 

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