Figure 6.1 The complexity of metabolism. Figure 6.5 The relationship of free energy to stability,...

Figure 6.1  The complexity of metabolism

Figure 6.5 The relationship of free energy to stability, work capacity, and spontaneous change

Figure 6.6  Energy changes in exergonic and endergonic reactions

Figure 6.7 Disequilibrium and work in closed and open systems

Figure 6.8 The structure and hydrolysis of ATP

Figure 6.9  Energy coupling by phosphate transfer

Figure 6.10 The ATP cycle

Figure 6.11 Example of an enzyme-catalyzed reaction: Hydrolysis of sucrose

Figure 6.12 Energy profile of an exergonic reaction

http://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf

Figure 6.13 Enzymes lower the barrier of activation energy

Figure 6.14 The induced fit between an enzyme and its substrate

Figure 6.15 The catalytic cycle of an enzyme

Figure 6.16 Environmental factors affecting enzyme activity

Characterizing enzymes

• Vmax - rate when enzyme is saturated with substrate

• KM – substrate concentration that allows reaction to proceed at 1/2 Vmax

• KM – useful as a measure of how tightly an enzyme binds its substrate– Low KM means tight binding, high KM

means weak binding

• Enzyme kinetics

Characterizing enzymes

• Turnover number: Vmax/enzyme concen.

– typically about 1000 substrate molecules processed per second per enzyme molecule, but can be much higher

Enzyme Turnover number (per second)

Carbonic anhydrase 600,000

Acetycholinesterase 25,000

Amylase 18,000

Penicillinase 2,000

DNA Polymerase 15

Measuring enzyme activity

• One unit of an enzyme is defined as the amount that will catalyze a defined amount of substrate in one minute under specified conditions.

• For catalase:

one unit decomposes 1mole H2O2 at 250C at pH 7.

What to measure for rate?

• Amount of substrate used over a specified time.

OR

• Amount of product accumulated over a specified time.

• Which to use???

Figure 6.17 Inhibition of enzyme activity

Figure 6.18 Allosteric regulation of enzyme activity

Figure 6.19 Feedback inhibition

Figure 6.20 Cooperativity