Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 431	Biochemistry	Fall 2007
Lecture Notes: 22 October	© R. Paselk 2007
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Introduction to Vitamins and Cofactors, cont.

Fun facts:

• Folate and Cobalamin deficiency both give rise to megaloblastic anemia, however cobalamin deficiency also results in irreversible CNS damage.
• In contrast to most water soluble vitamins, the lipid soluble vitamins can be taken in excess, with toxic results:
  • Excess vitamin D (actually a hormone) causes excess Ca²⁺ buildup with precipitation to form kidney stones and precipitates in tissues. Deficiency results in rickets.
  • Excess vitamin A can cause exfoliation.

Note the relationships of the various cofactors to their vitamin precursors.

Nucleotide Functions: Most involve use of the nucleotide as a recognition molecule, e.g. ATP (text Figure 1-25)

Nicotinamide Adenine Dinucleotide (NAD⁺) (text Figure 8-41-2) uses ADP (bolded) as a recognition "handle." (Note the two nitrogenous bases each attached to a ribose and linked through a phosphoric acid anhydride linkage:

Similarly adenosine with a modified ribose (reduced to the alcohol - ribitol) is used in Flavin Adenine Dinucleotide = FAD (text Figure 8-41-3; not truly a dinucleotide since ribitol instead of ribose!):

Coenzyme A (text Figure 8-41-1) has an ADP attached to an arm of pantothenic acid, which in turn is attached to beta-mercaptoethylamine. Acetyl groups can be carried on the sulfhydryl group:

To summarize, all three of these cofactors have ADP recognition portions which enzymes etc. can bind. (text Figure 8-41)

Three vitamins give cofactors with long "arms" which enable the cofactors to shift an attached substrate between adjacent active sites on a single enzyme. (Note attachment of biotin and lipoate to lysine side-chain to give 10 atom arms.)

Pathway Diagrams

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Last modified 22 October 2007