chapter 7- cofactors

explain what the plots mean

• a) chymotrypsin works best near neutral to slight basic conditions

• b) peak at ph 8 → His57 being deprotonated

  • His57 acts a general base

  • if His57 is protonated → slow catalysis

• c) low pH → binding is stron

  • after pH 8 → amino groups of lle becomes deprotonated

  • so weak substrate binding

what is another name for cofactors?

• vitamins

• important to understand because a deficiency can create disease

cofactor vs coenzyme

• cofactor:

• coenzyme: helps an enzyme catalyze a reaction by transferring atoms or electrons

• non protein chemical helpers that enzymes need to fucntion properly

What is SAM?

• S-adenosylmethionine

• synthesized by the reaction of methionine with ATP

• reacts readily with the nucleophilic acceptors

• donor of almost all the methyl group

what is this reaction important?

• SAM is required for conversion of norepinephrine to epinephrine

what are NAD(P)+ and NAD(P)H? why are they important?

• NAD+ → nicotinamide adenine dinucleotide (accepts electrons to become NADH)

• NADP+ → nicotinamide adenine dinucleotide phosphate (accepts electrons to become NADPH)

• Important as they are used in redox reactions

what is niacin?

• wear NAD+ and NADP+ come from

• two forms: nicotinic acid and nicotinamide

• vitatmin B3

• need 12-14 mg/day

• in animals, fruit, seeds, fungi

• can synthesize from tryptophan but we can not synthesize tryptophan

how do the structures of NAD+(NADP+) and NADH (NADPH)differ?

• NAD+ : is in oxidized form so it has one H

• NADH: is in reduced form so it has two H

what is lactate dehyrogenesase (LDH)?

• a NAD-dependent dehydrogenase

• NAD+ is reduced to NADH

  • gains electrons from lactate

• lactate is oxides to pyruvate

  • loses electrons

• shows how NAD+ is important for electron flow

what so dehydrogenases contain?

• rossman fold motifcation

• so beta-alpha-beta-alpha-beta units

hoe does ethanol metabolism work?

• 1: ethanol to acetaldehyde

  • uses alcohol dehydrogenase

  • NAD+ reduced to NADH

  • ethanol oxidized to acetaldehyde → toxic!!

• 2: acetaldehyde to acetate

  • uses acetaldehyde dehydrogenase

  • NAD+ is reduced to NADH

  • acetaldehyde is oxidized to acetate

what is FAD and FMN?

• FAD: flavin adenine mononucleotide

• FMN: flavin mononucleotide

• it is from riboflavin (vitamin B2)

• used by flavoproteins