Page 278 - Color Atlas of Biochemistry

Digestion 269

A. Digestive juices

Saliva Endoenzyme
Daily secretion 1.0–1.5 l
pH 7 Exoenzyme
Water Moistens food
Salts
Mucus Lubricant Compo- Function
Antibodies Bind to bacteria nents or substrate
α-Amylases (3.2.1.1) Cleave starch
Lysozyme (3.2.1.17) Attacks bacterial cell walls
Gastric juice
Daily secretion 2–3 l
pH 1
Bile Water
Daily secretion 0.6 l Salts
pH 6.9–7.7 HCl Denatures proteins,
Water kills bacteria
HCO 3 Neutralizes gastric juice Mucus Protects stomach lining
Bile salts Facilitate lipid digestion Pepsins (3.4.23.1-3) Cleave proteins
Phospholipids Facilitate lipid digestion Chymosin (3.4.23.4) Precipitates casein
Bile pigments Waste products Triacylglycerol lipase (3.1.1.3) Cleaves fats
Cholesterol Waste product Intrinsic factor Protects vitamin B 12

Pancreatic secretions
Daily secretion 0.7–2.5 l
pH 7.7 (7.5–8.8)
Water
HCO 3 Neutralizes gastric juice
Trypsin (3.4.21.4) Proteins
Chymotrypsin (3.4.21.1) Proteins
Elastase (3.4.21.36) Proteins
Carboxypeptidases (3.4.n.n) Peptides
α-Amylase (3.2.1.1) Starch and glycogen
Triacylglycerol lipase (3.1.1.3) Fats
Co-Lipase Cofactor for lipase
Phospholipase A (3.1.1.4) Phospholipids
2
Sterol esterase (3.1.1.13) Cholesterol esters
Ribonuclease (3.1.27.5) RNA
Deoxyribonuclease I (3.1.21.1) DNA

Secretions of the small intestine
Daily secretion unknown
pH 6.5–7.8
Aminopeptidases (3.4.11.n) Peptides
Dipeptidases (3.4.13.n) Dipeptides
α-Glucosidase (3.2.1.20) Oligosaccharides
Oligo-1,6-glucosidase (3.2.1.10) Oligosaccharides
β-Galactosidase (3.2.1.23) Lactose
Sucrose α-glucosidase (3.2.1.48) Sucrose
α, α-Trehalase (3.2.1.28) Trehalose
Alkaline phosphatase (3.1.3.1) Phosphoric acid esters
Polynucleotidases (3.1.3.n) Nucleic acids, nucleotides
Nucleosidases (3.2.2.n) Nucleosides
Phospholipases (3.1.n.n) Phospholipids

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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