chapter15

chapter15 - BCH 4054 Spring 2001 Chapter 15 Lecture Notes...

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Chapter 15, page 1 BCH 4054 Spring 2001 Chapter 15 Lecture Notes Slide 1 Chapter 15 Enzyme Regulation Slide 2 Enzyme Specificity • Molecular recognition through multiple interactions between substrate and enzyme • H-bonds, ionic forces, hydrophobic binding, van der Waals binding • Lock and Key Model (Emil Fischer) • Induced Fit Model (Daniel Koshland) • Example of hexokinase (See Fig. 15.1) Slide 3 Control of Enzyme Activity Product accumulation Substrate and coenzyme availability Synthesis and degradation of enzyme Covalent modification Allosteric regulation by “effector molecules” Specialized controls (zymogens, isozymes, modulator proteins)
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Chapter 15, page 2 Slide 4 Product accumulation and substrate availability • Products are generally inhibitors, and as they increase the back reaction increases. • Substrate availability can be important when the enzyme is not saturated, i.e. substrate is at K m or below. Slide 5 Synthesis and degradation of enzyme • Control at the level of gene expression Induction is the activation of enzyme synthesis Repression is the shutdown of enzyme synthesis • Protein degradation can also play a role sometimes. • Regulation is relatively slow, and requires considerable resource investment. Slide 6 Covalent modification • A faster means to control rate—don’t need to completely synthesize a new protein • Requires a reaction to activate, another to de-activate. • For example, phosphorylation- dephosphorylation (See Fig. 15.2) Converter enzymes must also be regulated, so interactions can become complex.
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Chapter 15, page 3 Slide 7 Protein Kinases • Over 100 known in yeast • Probably over 1000 in human genome • Phosphorylation at specific target sequences in proteins • Serine, Threonine, or Tyrosine • Find in many complex regulatory systems, from hormonal stimulation to gene activation to growth regulation. Phosphorylation and dephosphorylation is not the only method of regulation by covalent modification, though it is probably the most common. Slide 8 Zymogens (or “Proenzymes”) • Newly synthesized protein is inactive, and must be activated by proteolytic cleavage. • Proinsulin (See Figure 15.3) • Chymotrypsinogen (See Figure 15.4) • Blood Clotting proteins (See Figure 15.5) Slide 9 Isozymes • Enzymes with the same catalytic activity, but different kinetic properties which are adapted to needs of different tissues. • Hexokinase of brain versus glucokinase of liver (low K m in brain, high K m in liver) • Lactate Dehydrogenase • Two “types”, muscle (A) and heart (B) lead to five isozymes. (See Fig. 15.6) The heart type is inhibited by pyruvate, and is kinetically suited to convert lactate to pyruvate, which heart muscle can do. The muscle type is better suited kinetically to convert pyruvate to lactate. Of course the equilibrium position of the reaction would not be affected by either enzyme.
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Chapter 15, page 4 Slide 10 Modulator Proteins • Proteins that bind to enzymes and affect their activity.
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This note was uploaded on 05/22/2011 for the course BCH 4053 taught by Professor Logan during the Fall '06 term at FSU.

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chapter15 - BCH 4054 Spring 2001 Chapter 15 Lecture Notes...

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