CHEM 4420: Glycolysis: Lecture 3

What are the fat-soluble vitamins?

A, D, E, K

What are the water-soluble vitamins?

Vitamin B 1, 2, 3, 6, 12

What is the difference between coenzymes and cofactors?

Coenzymes are typically organic, while cofactors are often metals. Coenzymes DO bind to the active site, while cofactors DO NOT bind to the active site.

Vitamin B1 = (chemical name) + (active form)

Thiamine / thiamine pyrophosphate

Significant structures on Vitamin B1:

Thiazole ring joined to substituted pyrimidine; quaternary nitrogen (+) stabilizes (-) charged carbonyls

Vitamin B1 reactions:

Bonds to carbonyl carbons broken or formed; CHO metabolism, AA synthesis, pentose phosphate pathway

Vitamin B3= (chemical name) + (active form)

Niacin / nicotinamide adenine dinucleotide

What is the function of adenine nucleotide groups on vitamins/coenzymes?

NO catalytic reactivity; impacts specificity and binding affinity for the enzyme the substrate is binding to

How much energy is produced by breaking the phosphodiester bond?

\-30 kJ/mol

Which of the B vitamins are coenzymes?

B2, B3, B5

Disease caused by niacin deficiency

3D disease (Pellagra)

Theory as to niacin deficiency’s relation to dementia?

Niacin can be synthesized from tryptophan; if niacin stores are low, then tryptophan levels must be low, which is associated with Alzheimer’s syndrome

RDA Vitamin B3/niacin, sources

16 mg/d; Special K, braised calf liver, chicken breast

Vitamin B2= (chemical name) + (active form)

Riboflavin / flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)

Components of Vitamin B2 structure:

flavin (isoalloxazine ring), ribitol (sugar alcohol), mononucleotide

Vitamin B4 = (chemical name) + (active form)

Adenine / adenine

Vitamin B5 = (chemical name) + (active form)

Pantothenic acid / coenzyme A

Components of vitamin B5 (active form) structure:

Reactive terminal SH group \*\* part of beta-mercaptoethylamine, pantothenic acid, 3’,5’-ADP

What is the significance of the SH group on CoA (vitamin B5)?

It activates an acyl group for later transfer via nucleophilic attack. The thioester is more favorable than if CoA had a terminal OH group and formed an oxygen ester because thioester hydrolysis upon group transfer has a more negative delta G than oxygen ester hydrolysis

RDI of Vitamin B5

4 mg

What is the 4-phosphopantotheine group?

Pantothenic acid part + beta-mercaptoethylamine (end part of molecule ending in SH group) on CoA

What is the role of the 4-phosphopantotheine group?

FA chain transporter in FA synthesis; carrier of acyl group at start of TCA cycle, thioester hydrolysis

Vitamin B6 = (chemical name) + (active form)

Pyridoxine / pyridoxal phosphate (PLP)

What reactions are vitamin B6 involved in?

AA rxns; transamination, alpha-decarboxylation, beta-elimination. Binds to the active site of an enzyme via a Schiff base with a lysine residue. Stabilizes reaction intermediates via a conjugated “electron sink” mechanism—electron withdrawal away from the alpha-carbon of the AA to the cationic imine intermediate and the pyridoxal ring induces reactivity in AA substituents.

RDI vitamin B2:

1\.1 mg

RDI vitamin B1

1\.5 mg

RDI vitamin B3

16 mg

RDI vitamin B4

4 mg

RDI vitamin B5

4 mg

RDI vitamin B6

2 mg

RDI vitamin B7

300 mcg

RDI vitamin B9

500 mcg

RDI vitamin B12

2\.4 mcg

RDI vitamin A

900 mcg

RDI vitamin D

20 mcg

RDI vitamin C

60 mg