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Revision as of 04:07, 25 October 2006

Contents 1 Exam 1 Summary 2 Proteins continued 2.1 Enzyme kinetics 2.1.1 Inhibition 2.1.1.1 Irreversible Inhibitors 2.1.1.2 Reversible Inhibitors 2.1.1.2.1 Competitive Inhibitors 2.1.1.2.2 Non-competitive Inhibitors 2.1.1.3 Multiple-substrate Enzymes and Inhibition 2.1.1.3.1 Double Displacement Reactions

Exam 1 Summary

• no questions on cell biology stuff
• know all structures, even those barely mentioned
• go get exam from him if you'd like it

Proteins continued

Enzyme kinetics

Inhibition

• There are two types of inhibitors: irreversible, and reversible (which is made up of competitive and non-competitive)

Irreversible Inhibitors

• These inhibitors bind at the active site and cannot be taken off
• Example:
  • di-isopropyl flourophosphate on chymotrypsin
  • It binds to serine 195 and stops the enzyme from catalyzing.
  • Can be used to identify the active site amino acids.

Reversible Inhibitors

• The more inhibitor is added the less the enzyme works.

Competitive Inhibitors

• Usually, these inhibitors look like the substrate that the enzyme is supposed to bind with.
• Example: Succinate dehydrogenase
  • Succinate + FAD -> Fumarate (which is oxidized) + FADH2 (which is reduced)
  • If we put malonate in as an inhibitor, it binds as would succinate but electrons cannot be used for redox reaction because malonate does not have the carbons in the middle of the chain to donate them.
• So when you add competitive inhibitors:
  • Vmax does not change
  • Km increases
  • The slope of the reaction graph increases (because m = Km / Vmax)
• It makes sense that Vmax doesn't change because we are not changing the enzyme's ability, only how often the right substrate lands in the active site.

Non-competitive Inhibitors

• Does not bind where substrate binds.
• Example:
  • Add a heavy metal --it usually binds to SH group
• Note that these are not the same as allosteric affects
• So when you add non-competitive inhibitors:
  • Vmax decreases
  • Km stays constant
  • The slope of the reaction graph increases (because m = Km / Vmax)
• It makes sense that Vmax decreases because we are affecting the enzymes ability in a physical way.
• Likewise, it makes sense that Km remains constant because we are not changing how often the proper substrate lands in the active site.

Multiple-substrate Enzymes and Inhibition

• A + B -> P + Q
• We can study them by making them pseudo first order by saturating them with one of the reagents (A or B)
• The sequence of adding substrates can matter. If it does, it is called ordered, if it doesn't it is called random.
  • Random example: Creatin + ATP -> ADP + Creatin-p and it doesn't matter what order you add them.
  • Ordered example: Malate + NAD+ -> oxaloacetate + NADH+ and the NAD+ must be added first, then the malate.

Double Displacement Reactions

• These are also called ping-pong reactions.
• You bring in one substrate and release one product then repeat the process for each substrate.
• Example: Aspartate transaminase
  • Aspartic acid + alpha-ketogluterate -> oxloacetate + glutamic acid

1. Bind aspartic acid, then shift the amine to the pyridoxyl phosphate via shiff base formation.
2. Oxloacetate leaves
3. Alpha-ketogluterate binds, then transfer the amine from pyridoxyl phosphate to alpha-ketogluterate to produce glutamic acid.
4. Glutamic acid leaves.