cofactors and vitamins

Question 1

Thiamin aka vitamin B1

Answer 1

first water-soluble vitamin discovered, deficiency causes beriberi, acts as cofactor for decarboxylation reactions by being converted to thiamine pyrophosphate in pyruvate dehydrogenase

Question 2

Riboflavin aka vitamin B2

Answer 2

composed of ribose and flavin; 2 cofactor forms- FMN and FAD. Flavin residue serves as H+ acceptor in oxidation/desaturation reactions. e.g. fatty acyl CoA desaturase

Question 3

Niacin aka vitamin B3

Answer 3

used in NAD synthesis Deficiency leads to pellagra- dermatitis, diarrhea and dementia. NAD also acts as cofactor in alcohol dehydrogenase by accepting alcohol Hs to form NADH

Question 4

Pantothenic Acid aka coenzyme A aka vitamin B5

Answer 4

used in acyl-transfer reactions through formation of thioester linkage

Question 5

Lipoic Acid

Answer 5

acts as cofactor covalently bound to lysine. Covalently bound to pyruvate dehydrogenase Where it accepts acetyl group and transfer it to CoA to form acetyl coA. Oxidized form of lipoyllysine is then regenerated by FAD to FADH2 reaction

Question 6

Pyroxodal phosphate aka vitamine B6 aka pyroxidine

Answer 6

all aminotransferases use this linked to ε amino group of lysine. Work by transferring amino group to pyridoxal part of coenzyme to give pyradoxamine phosphate which reacts with α ketoacid to form the amino acid. Keq near 1, so reversible
* DOPA Decarboxylase uses this cofactor. Deficiency is linked to Parkinson’s and excess linked to schizophrenia

Question 7

Biotin

Answer 7

converted to coenzyme form biotinyllysine by formation of amide bond to N of lysine. Acts as cofactor in reactions that add carboxyl groups

Question 8

Vitamin B12

Answer 8

contains metal ion cofactor Co2+; involved in methyl transfer reactions and mutate reaction. Most important reaction is methionine synthase converting homocysteine to methionine using methyl from N5-methyl tetrahydrofolate (N5-THF). Methyl is transferred from THF to cobalt ion B12, then to sulfur on homocysteine.

Question 9

Folic Acid

Answer 9

• converted to coenzyme by addition of glutamate residues to carboxylate of other glutamate residues on folate, then pterin ring system of folate reduced by dihydrofolate reductase (DHFT) to give tetrahydrofolate (THF)
  
  • DHFT is cancer drug target of methotrexate. Binds to active site of DHFT, and prevents production of nucleic acid bases since THF is needed

Question 10

Ascorbic Acid aka Vitamin C

Answer 10

cofactor for hydrolase enzymes and acts as anti-oxidant

Question 11

Vitamin K

Answer 11

only fat soluble vitamin that is a cofactor. Involved in modifying proteins in clotting pathway by post-trnanslational modification. Ket cofactor in γ-flutamyl carboxylase that carboxylates residues on clotting factors to crease γ-carbocyglutamate residues