Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 438

Introductory Biochemistry

Spring 2007

Lecture Notes: 22 February

© R. Paselk 2006
 
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Enzyme Catalysis, cont.

Stabilization of Transition State Conformation: (Strain/distortion; Charge neutralization)

Strain/distortion example: Alkyl phosphate hydrolysis:

The base-catalyzed hydrolysis of A takes place more than one-hundred-million times faster than that of B, apparently due to the strain in the five membered ring in A.

Metal ion catalysis: metal ions can act as electrophilic catalysts in covalent type catalytic mechanisms and also as counter ions in charge stabilization in TS catalytic mechanisms.

Enzyme Examples of Catalysis

Now want to put it all together and look at example enzymes to try to explain their activities.

Lysozyme: Have looked at model of Lysozyme - globular with cleft to accommodate substrate (overhead; model). Functions as an antibiotic, hydrolyzing polysaccharide strand in cell walls of bacteria. For Lysozyme the substrate is a carbohydrate polymer. (Figure 6.17) [overhead].

Evidence:

So now let's look at the enzyme itself:

Chymotrypsin: (digestive enzyme: zymogens-precursor protein has peptide covering active site, activated by having it hydrolyzed off).

CARBOHYDRATES

  The carbohydrates, or sugars, are our third group of biomolecules. They are characterized by having a carbonyl carbon (aldehyde or ketone) and multiple hydroxyl groups. The smallest sugars are thus the three carbon trioses, glyceraldehyde (aldotriose) and dihydroxyacetone (ketotriose).
Note that sugars occur in both D and L forms. As we shall see the natural sugars are generally D.


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Last modified 22 February 2007