2014/9/25 1 Metabolism of common dietary saccharides and alcohol Lactose milk sugar, a disaccharide consisting of glucose & galactose lactase deficiency Fructose a common food ingredient and implicated in the development of certain chronic diseases Ethanol social drinking chronic alcoholics impact on people with compromised hepatic function http://www.web-books.com/MoBio/Free/Ch4H1.htm Lactose [galactosyl β (14)-glucose] synthesis. Protein B only found in lactating mammary glands, stimulated by prolactin. lactase
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2014/9/25
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Metabolism of common dietary saccharides and alcohol
Lactose
milk sugar, a disaccharide consisting of glucose & galactose
lactase deficiency
Fructose
a common food ingredient and implicated in the
development of certain chronic diseases
Ethanol
social drinking
chronic alcoholics
impact on people with compromised hepatic function
http://www.web-books.com/MoBio/Free/Ch4H1.htm
Lactose [galactosyl β (14)-glucose] synthesis.
Protein B only found in lactating mammary glands,
stimulated by prolactin.
lactase
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Pathway for galactose metabolism
GALT
Galactose kinase
GALT = galactose 1-phosphate uridyltransferase
UDP-hexose
4-epimerase
Key concept map for metabolism of fructose and galactose
GALT = galactose 1-phosphate uridyltransferase
Galactose converts to galactitol
Remove fructose and
sucrose from the diet
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Fructose
Dietary sources: as fructose (fruit sugar, honey) or high fructose corn
syrup (in soft drink)
• GLUT 5 transcription increases with increase fructose availability
•Entry into cells is NOT insulin-dependent
•Does not promote insulin secretion
http://en.wikipedia.org/wiki/Fructose
Phosphorylation products of fructose and their cleavage
pathways of energy metabolism Lippincott’s Illustrated Reviews : Biochemistry, 2011
• Hexokinase has low affinity for fructose
with the presence of glucose to saturate hexokinase,
little fructose is phosphorylated by hexokinase (to
form F 6-P).
• Fructokinase (found in liver and intestine) converts F to F 1-P
• F 1-P is then cleaved by Aldolase B
• Rate of F metabolism is more rapid than G
trioses formed from F 1-P bypass PFK-1 regulation, the
rate limiting step in glycolysis
What are the metabolic consequences of chronic high
fructose intake?
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Johnson R J et al. Endocrine Reviews 2009;30:96-116
Bray GA et al., Am J Clin Nutr. 2004 Apr;79(4):537-43
Total fructose : the sum of free fructose and fructose that is part of the disaccharide sucrose. Free fructose: the monosaccharide in HFCS and is also obtained in small amounts from other sources.
Fructose and Health
Effect of fructose on various organ systems
Basciano A et al. Nutr Metab 2:5-18, 2005
Euglycemic
hyperinsulinemic clamp
is a technique to assess
insulin resistance in
human and experimental
animals
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Nutrition Reviews 63:133-157, 2005
?
Basciano A et al. Nutr Metab 2:5-18, 2005
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Impacts of alcohol consumption on intermediary metabolism
~ 80% absorbed in duodenum and 20% in the stomach 7 kcal per gram of ethanol Main site of metabolism is the liver, but metabolites could also affects organs such as the CNS (ethanol-induced oxidative stress)