Cofactors are getting Real

What is an enzyme - cofactor

apoenzyme

Enzyme + cofactor

holoenzyme

Essential ions

• activator ions: weakly bound

• Metal ions: tightly bound

Coenzymes

• Cosubstrates = weakly bound

• Prothestic groups = tightly bound

Essential ions characteristics:

• these are minerals and MUST be obtained from the diet

• Activator and metal ions are both required by all organsims as enzyme cofactors

• activator ions = readily exchanged from enzyme

• metal ion = in metalloenzymes or part of prosthetic groups

cosubstrates:

• exhibit weak and reversible bind to the enzyme

• participate as necessary substrates in the reactions

• located at catalytic center

• replaced after each reaction by displacement/replacement

prosthetic groups

• tight binding and no dissociation

• can be covalently attached to the enzyme

• regenerated as needed while still bound to enzyme.

T/F: vitamins are usually needed as coenzymes or the starting compounds for making coenzymes

true

Metal activated essential ion cofactor

metal binding to enzyme or substrate changes structure or properties of the complex

Metalloenzymes

metal plays a direct role in catalysis

What is this:

• Weakly bound ions exhibiting reversible binding

• often necessary for substrate binding

• most common metals bound to enzymes are: K+, Mg²+, Ca²+

Metal activated enzymes

What are the two mains types of coenzymes

• Essential ions: activtor ions + metal ions

• coenzymes: cosubstrates + prothestic groups

Why does Mg2+ bind to ATP?

This is an example of a metal binding to a substrate: ATP is a substrate for many enzymes. Often Mg²+ must bind to the ATP, reducing the negative charge around the phosphates and stabilizing binding of ATP to an enzyme.

• The Mg²+ facilitates nuceophilic attach of phospjate groups

• Magnesium coordinates with the oxygen on the alpha and beta phosphate to neturalize the charge on them.

T/F: in metalloenzymes the metals bind tightly and remain bound to the enzyme

true

What is one example of metal binding and stabilizing a structure:

Ca²+ controls neutrotransmitter Ca²+ channels and Calmodulin acts as a calcium sensor.

• The protein, calmodulin, interacts with the control domain of the Ca²+ channel

  • Ca²+ binding changes the conformation of calmodulin

  • Ca²+ binds to the N-lobe and C-lobe of CaM

  • Calmodulin has 4 different binding sites for Ca²+ and each one has a little different specificity —> binding of one Ca²+ affects the binding of another.

The conc of calcium dictates whether calmodulin is bound with calcium or if the calcium levels in the cell are low, then Ca2+ gets released from calmodulin.

How does Fe²+ interact with the heme group?

• Fe²+ functions in hemoglobin to bind O2

• Fe²+ is the most common metalloenzyme ion and often transfers electrons in oxidation-reduction reactions.

Does Fe²+ bind as part of the prosthetic group?

YES! It binds heme in the globs and cytochromes.

Iron-sulfur clusters:

Fe²+ binds with sulfur as a prosthetic group of specific composition and geomertry. Strong reduction potential.

What is ATP?

It transfers a phosphoryl or nucleotidyl group —> cosubstrate

What does nicotinamide adenine dinucleotide do?

• Oxidation-reduction reactions involving two electron transfer

• cosubstrate

What does flavin mononucleotide (FMN) and Flavin adenine dinucleotide (FAD) do?

• Oxidation-reduction reactions involving one and two electron transfers

• Prosthetic group

S-Adenosylmethionine:

transfer of methyl groups —> cosubstrate

Coenzyme A does?

transfer of acyl groups → cosubstrate

Draw ATP

What is the charge of ATP at PH7 when there is no Mg²+

-4

What is the charge of ATP at Ph7 when there is Mg²+

It is -2 —> the magnesium coordiantes with the oxygen on the alpha and beta phosphate to neutralize the charge on both of them. This leaves a negative 2 charge

How do we label sugars in the ring

with primes

T/F: ATP can donate a variety of its parts in different reactions

true!

phosphoryl (1 PO4) → donor

-pyrophosphoryl ( 2 PO4’s) → donor

-adenosyl (AMP) → donor

What is Nicotinamide Adenine Dinucleotide (Phosphate) – NAD(P) involved in

oxidation - reduction reactions

What is a hydride?

2 electrons and one proton

• NAD+ is reduced to NADH

T/F: only the nicotinamide part is involved in the oxidation or reduction charge

true!

T/F: Frequently reduction reactions involve a gain of a proton with the gain of the electron

true