5.2 Enzyme Classifications (how diff enzymes fxn)

Enzyme Classifications

→ enzymes are classified by the rxns & processes they catalyze

• not fixed to a class

• enzyme classification DOESN’T change based on the direction of rxn

KNOW the names of the classes & what they do

1. Oxidoreductases

Oxidoreductases = catalyse oxido-reductions

• substrate is oxidized & regarded as the hydrogen or electron donor

• classification is based on donor:acceptor oxidoreductase

• types: dehydrogenases, oxidases, reductases

  • dehydrogenates typically involve cofactors (NAD+, FAD)

ex. alcohol dehydrogenase

ex. GAPDH in glycolysis

2. Transferases

transferases = transfer a group (methyl or glycosyl group) from one compound (donor) → another compound (acceptor)

• classification is based on donor:acceptor grouptransferase

• types: kinases (phosphate transfer enzymes)

ex. ATP-protein transferase

ex. hexokinase, PFK-1, PGK, and PK in glycolysis

Q. what is a more common name of the enzyme ATP:D-hexose 6-phosphotransferase?

hexokinase

• a transferase in glycolysis

3. Hydrolases

Hydrolases = catalyze hydrolysis reactions

• named after substrate w suffix -ase

• types: protease, collagenase, hyaluronidase

ex.

4. Lyases

Lyases = cleave C-C, C-O, C-N bonds by means OTHER than hydrolysis or oxidation

• 2+ substrates are involved in one rxn direction, BUT one compound less in the other direction

• when acting on the single substrate, a molecules is eliminated → generates a new double bond or a new ring

• often named “synthases”

• carry out addition or elimination rxns

• types: dehydratases & decarboxylases

ex. hydration of a double bond (addition rxn)

→ differentiate from hydrolysis by the presence of only one product after addition of water?

ex. aldolase & enolase (elim. rxn) in glycolysis

note: synthases are typically lyases, while synthetases are ligases

5. Isomerases

isomerases = catalyze structural rearrangements within a single molecule

• carry out isomerization rxns (relatively simple)

ex.

ex. PGI, PGM, & TPI in glycolysis

6. Ligases

ligases = catalyze the joining of 2 molecules or 2 parts of a molecule within concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate

• often named “synthetases"

ex. DNA ligases

ex. CAC succinyl-CoA synthetase

7. Translocases

Translocases = catalyze the movement of ions or molecules across membranes or their separation within membranes

• 1° active transport

Enzyme Classification Number

→ provides info about a reaction (4 digit codes)

• creates a reference system

note: trypsin & chymotrypsin have different specificity

ex. Glycolysis enzymes

1. hexokinase: phosphotransferase

2. phosphoglucose isomerase: isomerase

3. phosphofructokinase: transferase

4. aldolase: lyase (elimination rxn)

5. triose phosphate isomerase: isomerase

6. glyceraldehye phosphate dehydrogenase: oxidoreductase

7. phosphoglycerate kinase: transferase

8. phosphoglyceromutase: isomerase

9. enolase: lyase (elim rxn)

10. pyruvate kinase: transferase