Enzymes

Question 1

Salivary/lingual glands
pH of saliva: 6.8 – 7.2

Salivary α- amylase (ptyalin)

Answer 1

Enzyme class: Glycosidase, Endoglycosidase
Specific activator: Cl-
Substrate: Starch, glycogen
Action mechanism: Hydrolysis of internal α 1,4 glycosidic bonds
Potential products: Dextrins, maltotriose, maltose, isomaltose

Question 2

Salivary/lingual glands
pH of saliva: 6.8 – 7.2

Lingual lipase (characteristic for newborns, infants)

Answer 2

Enzyme group: Esterase
Substrate: Triacylglycerides
Action mechanism: Hydrolysis of ester bonds
Potential products: Fatty acids, 1,2-diacylglycerols, rarely monoacylglycerols

Question 3

Stomach
(chief cells)
pH of gastric juice: 1 – 2

Pepsin (Pepsinogen)

Answer 3

Enzyme group: Peptidase, Endopeptidase
Specific activator: HCl, autocatalysis
Substrate: Proteins (polypeptides)
Action mechanism: Hydrolysis of peptide bonds after aromatic AA (Phe, Tyr, Trp)
Potential products: Polypeptides, oligopeptides, tripeptides, dipeptides

Question 4

Stomach
(chief cells)
pH of gastric juice: 1 – 2

Gastric lipase *optimum pH 4-6

Answer 4

Enzyme group: Esterase
Substrate: Triacylglycerides
Action mechanism: Hydrolysis of ester bonds
Potential products: Fatty acids, 1,2-diacylglycerols, rarely monoacylglycerols

Question 5

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Pancreatic α-amylase

Answer 5

Enzyme group: Glycosidase, Endoglycosidase
Specific activator: Cl-, Ca2+ (for stabilization of active site)
Substrate: Starch, glycogen
Action mechanism: Hydrolysis of internal α 1,4 glycosidic bonds
Potential products: Dextrins, maltotriose, maltose, isomaltose

Question 6

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Trypsin (Trypsinogen)

Answer 6

Enzyme group : Peptidase, Endopeptidase
Specific activator: Enterokinase (enteropeptidase) and trypsin
Substrate: Proteins (polypeptides), peptides
Action mechanism: Hydrolysis of internal peptide bonds after basic AA (Arg, Lys, but NOT His)
Potential products: Shorter polypeptides, peptides (smallest product dipeptide)

Question 7

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Chymotrypsin (Chymotrypsinogen)

Answer 7

Enzyme group: Peptidase, Endopeptidase
Specific activator: Trypsin – proteolytical cleavage
Substrate: Proteins (polypeptides), peptides
Action mechanism: Hydrolysis of internal peptide bonds after aromatic AA (Phe, Tyr, Trp)
Potential products: Shorter polypeptides, peptides (smallest product dipeptide)

Question 8

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Elastase (Proelastase)

Answer 8

Enzyme group: Peptidase Endopeptidase
Specific activator: Trypsin – proteolytical cleavage
Substrate: Proteins (polypeptides), peptides
Action mechanism: Hydrolysis of internal peptide bonds after short AA (Ser, Thr, Ala, Gly, Cys)
Potential products: Shorter polypeptides, peptides (smallest product dipeptide)

Question 9

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Carboxypeptidase A (Procarboxy- peptidase A)

Answer 9

Enzyme group: Peptidase, Exopeptidase
Specific activator: Trypsin – proteolytical cleavage
Substrate: Proteins (polypeptides), peptides (smallest tripeptide)
Action mechanism: Hydrolysis of aromatic AA (Phe, Tyr, Trp) from carboxy- terminal end
Potential products: Shorter peptide (smallest product dipeptide) AND amino acid

Question 10

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Carboxypeptidase B (Procarboxy- peptidase B)

Answer 10

Enzyme group: Peptidase, Exopeptidase
Specific activator: Trypsin – proteolytical cleavage
Substrate: Proteins (polypeptides), peptides (smallest tripeptide)
Action mechanism: Hydrolysis of basic (Arg, Lys, but NOT His) from carboxy-terminal end
Potential products: Shorter peptide (smallest product dipeptide) AND amino acid

Question 11

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Pancreatic lipase
Colipase dependent (prevents inhibition)

Answer 11

Enzyme group: Esterase
Substrate: Triacylglycerides
Action mechanism: Hydrolysis of ester bonds
Potential products: Fatty acids, monoglycerols glycerol

Question 12

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Pancreatic lipase related protein-2

Answer 12

Enzyme group: Esterase
Substrate: Triacylglycerides, galactolipids, phospholipids
Action mechanism: Hydrolysis of ester bonds
Potential products: Fatty acids, monoacylglycerols, monoacylgalactosylglycerol, monoacylphosphoglycerol

Question 13

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Carboxyl ester lipase

Answer 13

Enzyme group: Esterase
Substrate: Triglycerides, galactolipids, phospholipids, cholesterol esters
Action mechanism: Hydrolysis of ester bonds
Potential products: Fatty acids, monoacylglycerols, monoacylgalactosylglycerol, monoacylphosphoglycerol cholesterol

Question 14

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Phospholipase A2

Answer 14

Enzyme group: Esterase
Substrate: Phospholipids
Action mechanism: Hydrolysis of ester bonds
Potential products: Fatty acids, monophosphoglycerol

Question 15

Pancreas
(acinar cells)
pH of pancreatic juice: 7.6 – 8.3

Polynucleotidase: Ribonuclease Deoxyribonuclease

Answer 15

Enzyme group : Esterase
Substrate: RNA - polynucleotides DNA - polynucleotides
Action mechanism: Hydrolysis of phosphodiester bonds between nucleotides
Potential products: Oligonucleotides, mononucleotides

Question 16

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

Glucoamylase (maltase-glucoamylase complex)

Answer 16

Enzyme group : Glycosidase, Exoglycosidase
Substrate: Oligosaccharides, dextrins, maltotriose, maltose
Action mechanism: Hydrolysis of terminal α-1,4- glycosidic bonds at nonreducing end
Potential products: Shorter oligosaccharide, Glucose

Question 17

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

β – glycosidase complex (lactase-phlorizin hydrolase)

Answer 17

Enzyme group : Glycosidase, Exoglycosidase
Substrate: Lactose, cellobiose, glycosyl-β- ceramides
Action mechanism: Hydrolysis of β 1,4 glycosidic bond
Potential products: Glucose and galactose

Question 18

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

Sucrase-isomaltase complex

Answer 18

Enzyme group : Glycosidase, Exoglycosidase
Substrate: Dextrins, maltose, maltotriose, isomaltose, sucrose
Action mechanism: Hydrolysis of α 1,2; both α-1,4- and α-1,6-glycosidic bonds
Potential products: Glucose; fructose, shorter oligoscahharides

Question 19

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

Trehalase

Answer 19

Enzyme group : Glycosidase, Exoglycosidase
Substrate: Trehalose (mushroom sugar)
Action mechanism: Hydrolysis of α 1,1-glycosidic bonds
Potential products: Glucose

Question 20

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

Nucleosidase

Answer 20

Enzyme group : Glycosidase
Substrate: Nucleoside
Action mechanism: Hydrolysis of N-glycosidic bond
Potential products: Pentose (Ribose or deoxyribose); purine or pyrimidine base

Question 21

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

Aminopeptidase
Zn2+ dependent metalloenzyme

Answer 21

Enzyme group : Peptidase, Exopeptidase
Substrate: Peptide (smallest tripeptide)
Action mechanism: Hydrolysis of any AA from N terminal
Potential products: Shorter peptide and amino acid

Question 22

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

Dipeptidase
Zn2+ dependent metalloenzyme

Answer 22

Enzyme group : Peptidase, Exopeptidase
Substrate: Dipeptides
Action mechanism: Hydrolysis of any dipeptide
Potential products: Amino acids

Question 23

Intestinal
mucosa
(absorptive cells)
pH of intestinal juice: 7.1 – 7.6

Nucleotidase

Answer 23

Enzyme group : Esterase
Substrate: Nucleotide
Action mechanism: Hydrolysis of ester bonds in nucleotide
Potential products: Nucleoside and phosphate