12_Fructose_and_Galactose_...pdf

1Fructose and Galactose  Metabolism And Carbohydrate Metabolism in Tissues What can we do with fructose and galactose? 1. Convert to glucose 2. Can be used to produce energy Liver is the major sight of fructose and galactose metabolism. - because hexokinase has a lower Km (higher affinity) for glucose vs. fructose and galactose Liver Glucokinase Fructokinase Galactokinase Muscle Hexokinase 2Fructose Metabolism Fructose Fructokinase ADP ATP Fructose 1-Phosphate Fructose 1-Phosphate + ADP Aldolase B DHAP + Glyceraldehyde DHAP + Glyceraldehyde Gluconeogenesis Aldolase Glyceraldehyde kinase or Triokinase Glyceraldehyde 3-Phosphate Glycolysis ATP ADP 3Fructose enters after PFK I Æ No rate control ÆMore triacylglycerol formation Excess fructose intake can lead to excess fatness Æ Increased risk of heart disease Glucose Triose Phosphate Pyruvate Acetyl CoA Fructose Fatty acids Triacylglycerol Metabolic Problems Associated with  Fructose ?  Fructosemia ? Excrete fructose in the urine ? Caused by lack of Fructokinase ?  Fructose Intolerance ? Results in hypoglycemia ?  Caused by lack of Aldolase 4Galactose Metabolism Galactose Galactokinase ATP ADP Galactose 1-phosphate Galactose 1-phosphate Galactose 1-phosphate uridyl transferase UDP-glucose Glucose 1-phosphate UDP - Galactose UDP - Galactose UDP-galactose 4-epimerase UDP - Glucose Glycogen Glycogen synthase 5Glycogen Glucose 1-Phosphate Glucose 6 Phosphate Glycogen phosphorylase - Glucose Glucose 6-phosphatase UDP-glucose can feedback to supply the substrate in galactose metabolism Galactose 1-phosphate UDP-glucose Glucose 1- phosphate UDP - Galactose UDP - Glucose Metabolic Problems Associated with Galactose ? Galactosemia ? missing galactose 1-phosphate uridyl transferase - Can cause liver failure, mental deterioration, and cataracts 6Carbohydrate Metabolism in Various Tissues I. Liver ? Involved in blood glucose homeostasis via the processes of: ? Gluconeogenesis - ? blood glucose ? Glycogenolysis - ? blood glucose ? Glycogenesis - ? blood glucose What occurs during low blood glucose (starvation)? ? Want to ? blood glucose ? Glucose is supplied to the blood in response to the following hormones: ? Glucagon ? promotes Gluconeogenesis & Glycogenolysis ? Epinephrine - ? Glycogenolysis ? Glucocorticoids - ? Gluconeogenesis 7What happens during high blood glucose (fed state)? ? ? Blood glucose ? In response to insulin: ? ? Glycogenesis, ? ? Glycolysis ? ? HMP shunt II. Muscle ? Predominate pathways: ? Glycolysis ? Glycogenolysis / Glycogenesis Uptake of glucose by the muscle enhanced by: 1. Insulin 2. Muscular Work/Exercise Occurs via Glucose transport protein (Glut 4) Æ transports glucose into the muscle. 8Products of glycogenolysis used in the muscle only, not delivered to the blood. ? Muscle can break down glycogen Æ glucose-6- phosphate; unable to convert glucose-6- phosphate to glucose ? Muscle lacks the enzyme: glucose-6- phosphatase ? Hexokinase enzyme: low Km for glucose III. Brain ? Predominate pathways 1. Glycolysis 2. TCA cycle ? Involved in aerobic metabolism ? Hexokinase: low Km for glucose Glucose can provide important carbon pre-cursors: ? Acetylcholine ? GABA ? Lipids 9IV. Erythrocytes (RBC?s) ? No mitochondria; restricted to anaerobic metabolism ? Predominate pathways: 1. HMP shunt 2. Anaerobic glycolysis 1. HMP shunt : source of NADPH + H+ GSSH NADPH + H+ NADP+ GSH (reduced) Glutathione reductase H2O2 H2O Glutathione peroxidase 2. Anaerobic glycolysis ? Source of: ? 2,3-bisphosphoglycerate (BPG) ? Emergency energy reserve ? Binds to Hb = lowers Hb affinity for O2Æ facilitates unloading of O2 to tissues ? Buffering agent 10 1,3-bisphosphoglycerate 2,3-bisphosphoglycerate 3-phosphoglycerate * Not substrate level phosphorylation V. Kidney ? Source of gluconeogenesis in an adapted fast VI. Adipose Tissue ? Predominant pathways: ? Glycolysis: source of glycerol-3-phosphate DHAP Glycerol-3-phosphate Triacylglycerol 11 2. HMP shunt ? Produces NADPH + H+ = used in the synthesis of fatty acids rgf09 Microsoft PowerPoint - 12 Fructose and Galactose Metabolism [Compatibility Mode]