Physiological and Metabolic Bases for Energy Expenditures. H d E,, Heat of Digestion IE = RE + HE + FE + GE + UE. H d E

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1 Physiological and Metabolic Bases for Energy Expenditures H d E,, Heat of Digestion Nutrition 202 Animal Energetics R. D. Sainz Lecture 06 IE = RE + HE + FE + GE + UE HE = H e E+ H d E+ H r E+ H j E+ H c E+ H f E RE = TE + LE There are two definitions of H d E, each with its own method of estimation H d E E.g., long-term -300 (comparative -400 slaughter): -500 H d E = ME m -NEm RE, kj/kg = kj/kg 0.75 = 75 kj/kg / 450 = 16.7% of ME (range 5 to 25%) MEm NEm ME intake, kj/kg

2 H d E E.g., short-term (calorimetry) costs of digestion, absorption and assimilation 8-14% of ME HE Meal Time H d E Long-term > short-term estimates These measurements involve quite different metabolic processes. Kellner Rubner Current H d E Nomenclature HIF heat increment of feeding (includes H f E) SDA specific dynamic action DIT diet-induced thermogenesis; refers to large HE in response to very high food intakes (e.g., cafeteria feeding) Thermic effect of food short-term H d E NRC, 1981 H d E heat of digestion, absorption & assimilation 2

3 Components of H d E Costs of ingestion Costs of digestive secretions Costs of bond breakage Costs of absorption Costs of assimilation Changes in metabolic activity due to intake Rubner Cost of eating fed bone meal + cellulose to dogs observed very small H Webster & others pigs, sheep, chickens H up to 50% during a meal, even with sham-feeding Response depends upon time spent eating NOT due to chewing, salivation H for rumination is much smaller Webster, 1980 Chopped hay Barley pellets % of ME Eating Rumination GI work Other H d E Fermentation HIF

4 Costs of digestive secretions Saliva, HCl very small energy cost GI & digestive proteins e.g. 250 kg steer secretes 350 g protein/day into GI tract (to be continued ) Protein synthesis (transport) 3 AA EC + 3 Na + EC + 2 K+ IC 3 AA IC + 3 Na+ IC + 2 K+ EC 3 Na + IC + 2 K+ EC + 1 ATP 3 Na+ EC + 2 K+ IC + 1 ADP + P i AA EC + 1 ATP 3 AA IC + 1 ADP or AA EC ATP AA IC ADP Protein synthesis (activation) AA + ATP AA-AMP-AAS + PP i AA-tRNA + AMP + AAS ATP + AMP 2 ADP AA + 2 ATP AA-tRNA + 2 ADP (AAS = aminoacyl-trna synthetase) 4

5 Protein synthesis (initiation, elongation, translocation & termination) AA-tRNA 1 + IF2 + GTP + P-site AA-tRNA 1 -P + GDP + IFs AA-tRNA 2 + EF1 + GTP + A-site AA-tRNA 2 -A + GDP EF1 AA-tRNA1-P + AA-tRNA 2 -A peptidyl-trna-a peptidyl-trna-a + EF2 + GTP peptidyl-trna-p + EF2 + GDP peptidyl-trna-p + RF + GTP peptide + RF + trna + GDP AA-tRNA + 2 GTP peptide bond + 2 GDP AA transport Activation Initiation Elongation Termination Total Protein synthesis (summary) ~P/mol Plus the costs of maintaining the synthetic machinery, ribosomes, enzymes, factors. So: ~ 5 ATP equivalents per peptide bond. Heat equivalent of ATP C 6 H 12 O O ADP 6 CO H 2 O + 31 ATP + heat 31 ATP 31 ADP + heat Net heat production: MJ MJ heat 31 ~P = MJ / ~P 5

6 Costs of digestive secretions Average molecular wt 110 g/mol amino acid in protein 350 g/day 110 g/mol = 3.2 mol AA/day 3.2 mol AA/day * 5 ~P/mol AA = 15.9 mol ~P/day 15.9 mol ~P/day * 90.8 kj/mol ~P (i.e., glucose) = 1,444 kj/day ME maintenance 450 kj/kg 0.75 * 62.9 kg ,000 kj/day So: cost of synthesizing digestive proteins is 1,444 28,000 = 5% of ME intake for maintenance Costs of bond breakage (e.g., starch) Starch: 17.5 kj/g * 162 g/mol glucose = MJ/mol glucose in starch Glucose: 15.6 kj/g * 180 g/mol glucose = MJ/mol glucose Cost of hydrolysis: = MJ/mol glucose = 0.6% of energy in starch Costs of bond breakage Similarly, for Proteins: 0.6% of energy in proteins (break peptide bonds) Triacylglycerols: 0.1% of energy in TAGs (break ester bonds) 6

1993. Understanding Nutrition. West Publishing Co., St. Paul, MN.

7 Costs of bond breakage H d E= ME m H e E These values must be corrected for the costs incurred in H e E, such as lipid mobilization (0.1%) So then we have: CH 2 O = 0.5% Protein = 0.5% TAG = 0.0% From: Whitney, EN and Rolfes, SR Understanding Nutrition. West Publishing Co., St. Paul, MN. Costs of absorption (glucose) As for AA transport above Glucose GI ~P glucose blood (active transport portion) (0.33 ~P/mol glucose * 90.8 kj/~p from glucose) / 2,816 kj/mol glucose = 1.0% 7

Costs of absorption (amino acids) As above, 0.33 ~P/mol (0.33 ~P/mol AA * 120 kj/~p from AA) / 2,360 kj/mol AA = 1.5% From: Whitney, EN and Rolfes, SR. 1993. Understanding Nutrition.

8 Costs of absorption (amino acids) As above, 0.33 ~P/mol (0.33 ~P/mol AA * 120 kj/~p from AA) / 2,360 kj/mol AA = 1.5% From: Whitney, EN and Rolfes, SR Understanding Nutrition. West Publishing Co., St. Paul, MN. Costs of absorption (tripalmitin) TAG GI 2-MAG + 2 FA 2 FA + 2 CoASH + 4 ATP 2 FA-CoA + 4 ADP 2-MAG + 2 FA-CoA TAG blood + 2 CoASH TAG GI + 4 ATP TAG blood + 4 ADP (4 ~P/mol TAG * 24.7 kj/~p from TAG) / 31,800 kj/mol TAG = 0.3% 8

9 Glucose: 1.0% Amino acids: 1.5% TAG: 0.3% Costs of absorption The costs derived here will depend upon a number of assumptions, therefore exact values may differ; The point is, absorption is energetically cheap. Animals are continuous metabolizers and discontinuous feeders. Costs of assimilation & storage E.g., human eating 3 30-minute meals/day 1.5 hours / 24 hours = 6.25% of day spent eating If absorptive period is 2 hours/meal, then 6/24 = 25% of time is absorptive, and 75% of time is post-absorptive 9

Costs of assimilation & storage (glycogen - short-term term CH 2 O storage) Glucose + ATP Glucose-6-P + ADP + Pi Glucose-6-P Glucose-1-P Glucose-1-P + UTP UDP-glucose + Pi UDP-glucose + Glycogen(n)

10 Costs of assimilation & storage (glycogen - short-term term CH 2 O storage) Glucose + ATP Glucose-6-P + ADP + Pi Glucose-6-P Glucose-1-P Glucose-1-P + UTP UDP-glucose + Pi UDP-glucose + Glycogen(n) Glycogen(n+1) + UDP UDP + ATP UTP + ADP Glucose + Glycogen(n) + 2 ATP Glycogen(n+1) + 2 ADP (2 ~P/mol glucose * 90.8 kj/~p from glucose) / 2,816 kj/mol glucose = 6.45% Lipogenesis From: Allen, CE, Beitz, DC, Cramer, DA, and Kauffman, RG Biology of Fat in Meat Animals. American Society of Animal Science, Chapaign, IL. Costs of assimilation & storage (glucose to fat - short-term) term) 13.5 glucose + 27 ADP 3 palmitate + 27 ATP 3 palmitate + 6 ATP + 3 CoASH 3 palmitoyl-coa + 6 ADP 0.5 glucose + ATP + NADH 2 α-glycerol-p + ADP + NAD + NAD ATP NADH ADP palmitoyl-coa + α-glycerol-p tripalmitin + 3 CoASH 14 glucose + 17 ADP tripalmitin + 17 ATP (Net) see p. 168, Table 6.6 in Baldwin 10

11 Costs of assimilation & storage (glucose to fat - short-term) term) 14 glucose ADP tripalmitin ATP Heat production = Hc of inputs - Hc of of outputs = (14 mol glucose*2.816 MJ/mol) (1 mol TAG*31.8 MJ/mol mol ~P* MJ/mol) = 39.4 MJ 32.4 MJ = 7.0 MJ/mol TAG = 17.7% of energy in glucose see p. 168, Table 6.6 in Baldwin Lipolysis From: Murray, RK, Granner, DK, Mayes, PA, and Rodwell, VW Harper s Biochemistry. Appleton & Lange, San Mateo, CA. Costs of assimilation & storage (glucose stored as fat and then mobilized - long-term) the long-term costs of glucose storage as fat are those associated with the conversion of acetyl-coa to fatty acids and the oxidation of fat to re-form acetyl-coa Net: 100 mol ~P / mol tripalmitin Heat loss = (100 mol ~P* MJ/mol) / (14 mol glucose*2.816 MJ/mol) = 9.08 MJ / 39.4 MJ = 23.0% see p. 169, Table 6.7 in Baldwin 11

12 From: Allen, CE, Beitz, DC, Cramer, DA, and Kauffman, RG Biology of Fat in Meat Animals. American Society of Animal Science, Chapaign, IL. Costs of assimilation & storage (assimilation & storage of dietary fat) TAG blood glycerol + 3 FA 3 FA + 3 CoASH + 6 ATP 3 FA-CoA + 6 ADP 0.5 glucose + ATP + NADH 2 α-glycerol-p + ADP + NAD 3 FA-CoA + α-glycerol-p TAG cell + 3 CoASH glycerol + ATP α-glycerol-p α-glycerol-p + NAD DHAP + NADH 2 DHAP 0.5 glucose TAG + 8 ATP TAG + 8 ADP Red denotes liver transactions. Costs of assimilation & storage (assimilation & storage of dietary fat) TAG + 8 ATP TAG + 8 ADP Heat production = (8 mol ~P* MJ/mol) / 31.8 MJ/mol TAG = 0.6% 12

13 Costs of assimilation & storage (use of protein for energy) AA intermediates Urea + CO 2 + H 2 O + ~P + heat Heat 15% of energy in protein Costs of assimilation & storage H d E Glucose glycogen Glucose fat (short-term) Glucose fat (long-term) Fat Protein 6.45% 17.7% 23.0% 0.6% 15% Costs of assimilation & storage (Baldwin, p. 165, Table 4) Assimilation costs vary from % (short-term) % (long-term) depending upon assumptions e.g. CH 2 O: 20% oxidized 30% stored as glycogen 50% stored as fat 13

14 Changes in metabolic activity between fasted & fed states deal with under H e E Bottom line H d E is about 5 25% of ME (observed) We accounted for % of ME (theoretical) Ingestion Secretions Bond breakage Absorption 2-3% 5% 0 0.5% % Assimilation % Conclusion Careful, quantitative analysis of metabolic costs CAN account for a majority of observed energy expenditures, over the short and long terms. 14

Physiological and Metabolic Bases for Energy Expenditures IE = RE + HE + FE + GE + UE

Physiological and Metabolic Bases for Energy Expenditures H d E,, Heat of Digestion Nutrition 202 Animal Energetics R. D. Sainz Lecture 06 IE = RE + HE + FE + GE + UE HE = H e E+ H d E+ H r E+ H j E+ H