BioChem Enzymes

Question 1

Hexo/Glucokinase

Answer 1

First step of glycolysis. Phosphorylates glucose to glucose 6 phosphate. Locks glucose into cell
Hexokinase: Inhibited by product G6P
NB: Inhibition of PFK leads to build up of G6P

Glucokinase (in liver): has higher Km then hexokinase
NB: not inhibited by products

Question 2

PFK

Answer 2

comitted step in glycolysis phorphorylates F6P->F16BP
Regulation: High ATP inhibits,
High AMP activates

Liver: Stimulated by F26BP F6P->F26BP by PFK2
inhibited by citrate

Question 3

Pyruvate Kinase

Answer 3

Last step in glycolysis breaks down PEP to Pyruvate
Regulation: Inhibited by ATP, alanine
Activated by F16BP via feed forward mechanism

Question 4

Pyruvate Dehdrogenase Complex

Answer 4

Large complex that converts pyruvate into Acetyl CoA after pyruvate has been shuttled into mitochondria
Reguatlion: phosphorylated and innactive
phorsphorylation increased by NADH, ATP and Acetyl CoA
Dephosphorylated and active. Phosphatase activity is increased by ADP, Pyruvate and Ca++

Question 5

Isocitrate Dehydrogenase

Answer 5

Step in TCA cycle takes isocitrate to A-ketoglutarate with CO2 and NADH
Regulation: Inhibited by ATP and NADH. Leads to build up of citrate via aconitase converting isocit to cit
Cit inhibits PFK and acts as source of Acetyl CoA for FAS

Question 6

Carnitine Shuttle

Answer 6

FA -> Acyl CoA via Acyl CoA synthetase
Carnitine shuttles acyl CoA across the inner mitochondrial membrane for FA degredation
Carnitine is recylced
Inhibited by malonyl CoA (precurrsor for FA synthesis)

Question 7

Acetyl CoA Carboxylase

Answer 7

Enzyme that transforms Acetyl CoA to Malonyl CoA for FAS
Regulation: AMP dependent protein kinase inactivates
Phosphatase activates
Citrate activates even inactive form
Insulin Stimulates
Glucagon, Epinephrine inhibit ACC

Question 8

Fatty Acid Synthase

Answer 8

Links malonyl CoA to Acetyl CoA to form long fatty acids. Need Malonyl ACP and Acetyl ACP

Question 9

Adipose Tissue Lipase

Answer 9

Hormone Sensitive Lipase and Perilipase involved in FA degredation
Regulation: Epinephrine/ glucagon stimulate

Question 10

Fructose 1,6 Biphosphatase

Answer 10

Enzyme that cleaves off phosphate in gluconeogenesis to form Fructose 6 Phosphate.
Inhibited by F26BP, AMP
Activated by citrate

Question 11

Pyruvate Carboxykinase

Answer 11

First step in gluconeogenesis takes pyruvate to OAA. OAA can be shuttled out of the mitochondria in the form of malate. Uses ATP
Inhibited by ADP
Activated by Acetyl CoA

Question 12

Glycogen Phosphorylase

Answer 12

Enzyme involved in breaking down glycogen
Takes piece of gylcogen and cleaves it to form glucose 1 phosphate
glucose 1 phosphate -> G6P via phosphoglucomutase
Regulation: Inhibited by G6P and ATP
Insulin leads to T state (less active) dephosphorylates a to b form
Glucagon leads to R state (more active)via phosphorylation of b form

Question 13

Glycogen Synthase

Answer 13

Builds glycogen molecule from UDP-glucose monomers. Requires primer glycogenin
Regulation: Phosphorylated and deactivated
Dephosphorylated and active
Activated by G6P

Question 14

Lipoprotein Lipase

Answer 14

Found in the lumen of the blood vessles. Breaks down FA carried on serum albumin. Allows for transport of FA into cells as FFA and monoacylglycerol

Question 15

PEP Carboxykianse

Answer 15

Converts OAA into PEP. Uses GTP

Regulation: Inhibited by ADP