Objectives Chapter 7 Protein Review the basic structure

Objectives: Chapter 7 - Protein • Review the basic structure of proteins and their component amino acids • Learn which are the essential amino acids and why • Understand that there are various amino acid “pools” within the body including dietary and body tissue pools • Learn how amino acids can be used for Ø The synthesis of new proteins for growth or replacement of cellular proteins Ø Production of important non-protein nitrogen containing molecules Ø Oxidation as an energy source Ø Synthesis of glucose, ketones or fatty acids • Understand how the liver and muscle handle amino acid metabolism, and how brain function is closely related to some amino acid metabolism • Learn how to determine the “quality” of the protein you eat, what the recommended intakes are and why

Functional roles of proteins: Structural organization Fig. 7 -1, p. 175

Table 7 -1 a 1, p. 178

Table 7 -1 a 2, p. 178

Key Ideas: the tertiary structure of a protein is determined by its amino acid composition and amino acid side chain chemistry determines what our bodies can do with them metabolically Table 7 -1 b, p. 179

Sources of Protein Exogenous Sources • Animal products such as meat, poultry, fish, and dairy products (not including butter, sour cream, or cream cheese) • Plant products such as grains, grain products, legumes, and vegetables Endogenous Sources • Desquamated mucosal cells (50 g protein/day) • Digestive enzymes and glycoproteins (17 g/day) (total daily requirement for protein for males is 56 g/day, for females it is 46 g/day)

Digestion of Proteins – pepsin only works on exogenous proteins, all other enzymes work on both exogenous and endogenous proteins Table 7 -2, p. 182

Step 2 Amino acid Na+ Step 1 Amino acid Cell membrane Na+ Amino acid transporter Na+ Cytosol Amino acid Intracellular amino acid metabolism Na+ Step 3 Na+ /K + ATPase Na+ Amino acid Step 4 Step 5 Fig. 7 -6, p. 183

Table 7 -3, p. 184

Amino Acid Supplements • Amino acids that use the same carrier system may create, depending on the amount ingested, a competition between the amino acids for absorption • Supplements may result in impaired or imbalanced amino acid absorption • Some amino acid supplements can cause serious illness • L-tryptophan • L-phenylalanine • Some amino acids are useful • L-lysine

Enterocyte Basolateral Membrane Lumen (small intestine) Peptide Carrier H 1 H 1 Na 1 K 1 Na 1 Brush border Membrane Fig. 7 -7, p. 184

Basolateral Membrane Enterocyte Na 1 Lumen ATP Na 1 ADP 1 Pi K 1 Amino Acid Amino acids Carrier Na 1 Required for some amino acid transport Brush border membrane Peptides Na 1 Amino Acids Fig. 7 -8, p. 185

Table 7 -4, p. 185

Many dietary amino acids are used by enterocytes and never make it into the circulation. This is an example of the fates of glutamine in the enterocyte. Fig. 7 -9, p. 186

Reduced Glutathione can also be made from glutamine in enterocytes Fig. 7 -10, p. 186

Metabolic Fates of Amino Acids • Synthesis – Plasma proteins (albumin, retinol-binding protein, acute phase proteins, heat shock proteins) – Nitrogen containing non-protein compounds (glutathione, carnitine, creatine, carnosine, choline) – Purines and pyrimidines • Catabolism • Transamination and deamination to keto-acids • Energy • Glucose • Ketone bodies • Cholesterol • Fatty acids • Ammonia disposal – urea cycle

Synthesis of plasma proteins

Synthesis of nitrogen containing, nonprotein compounds • Glutathione • Carnitine • Creatine • Carnosine • Choline • Purine and pyrimidine bases

Table 1. Effect of Oral Creatine Supplementation on Specific Activities Activity Summary of Studies Comments Stationary Several studies support an cycling ergogenic effect in repeated sprints but are not convincing for single sprints Field studies with bicycles on a track are needed to simulate actual competition Running sprints (repeated or single) Conflicting results regarding performance enhancement Speculation is that weight gain offsets any potential benefit Swimming Conflicting results regarding sprints performance enhancement (repeated or single) Speculation is that weight gain offsets any potential benefit Weight lifting Whether creatine supplementation truly increases muscle synthesis is being investigated. Creatine-induced weight gain may make true double-blindness difficult to achieve Some evidence of an ergogenic effect

Pyrimidine synthesis Fig. 7 -16, p. 192

Purine synthesis from ribose phosphate Fig. 7 -17 a, p. 193

Fig. 7 -17 b, p. 193

Gout

Amino Acid Metabolism • Deamination or transamination • Nitrogen recycling/disposal via urea cycle • Use of remaining carbon skeletons Fig. 7 -20, p. 195

Urea Deamination Fig. 7 -21, p. 196

Transamination Fig. 7 -22, p. 196

Fig. 7 -23, p. 197

A typical blood chemistry panel might include the following tests: General Metabolism Kidney Function Electrolytes Liver Function Thyroid Pancreas GLU (Glucose) LDH (Lactate dehydrogenase) CPK (Creatine phosphokinase) BUN (Blood Urea Nitrogen) CREAT Creatinine Na (Sodium) K (Potassium) Cl (Chloride) CA (Calcium) PHOS Phosphorus ALP (Alkaline phosphatase) ALT (Alanyl amino transferase) ALB (Albumin) GGT (Gammaglutamyl transpeptidase) SGPT (Serum glutamate pyruvate transaminase) TP (Total Protein) CHOL (Cholesterol) GLOB (Globulin) TBILI (Total Bilirubin) T 3 Triiodothyro nine) T 4 Thyroxine AMY (Amylase) LIP (Lipase)

If acetylco. A is abundant, but oxaloacetate is not glucogenic ketogenic Fate of carbon skeletons from amino acids Fig. 7 -24, p. 199

Metabolic fates of selected amino acids • Phenylalanine – tyrosine, melanin, thyroid hormones, Ldopa, dopamine, norepinephrine, acetyl co. A • Tryptophan – serotonin, melatonin, picolinate, NAD+, nicotinamide, NADP+, acetylco. A, pyruvate, xanthurenic acid • Methionine – homocysteine, spermidine, tetrahydrofolate, taurine, sulfate, succinylco. A • Lysine – carnitine, acetylco. A • Threonine – succinyl co. A, pyruvate, acetaldehyde

Fates of amino acids not used for the synthesis of body proteins Fig. 7 -31, p. 207

How do organs other than the liver get rid of the ammonia biproduct of amino acid metabolism? • Ammonia to glutamate to glutamine (glutamine synthetase; ATP; Mg 2+ or Mn 2+) • Alanine to pyruvate to glucose (transamination) • Branched chain amino acids to glutamate to glutamine to alanine (transamination)

Alanine-glucose cycle Fig. 7 -34, p. 209

Fig. 7 -38 b, p. 213

Kidneys prefer: Glycine, alanine, glutamate, phe, and aspartate From these it produces: Arginine, histidine, serine and maybe tyrosine It is the only organ other than the kidney that has gluconeogenic enzymes and is critically important during fasting. Fig. 7 -38 c, p. 213

You can also excrete urea via the skin, and can lose nitrogen via hair and skin cell loss. These losses are referred to as insensible nitrogen losses. Table 7 -5, p. 214

Fig. 7 -38 a, p. 213

How to Determine Protein Quality? • Digestibility • Composition with respect to indispensable amino acids – High quality or complete – Low quality or incomplete • Quantitative evaluation methods – – – Amino acid score Digestiblity corrected amino acid score Protein efficiency ratio Nitrogen balance Biological value Net protein utilization

Table 7 -6, p. 220

Table 7 -7, p. 222

Food Weight in grams Serving Protein grams % Daily Value Hamburger, extra lean 6 ounces 170 48. 6 97 Chicken, roasted 6 ounces 170 42. 5 85 Fish 6 ounces 170 41. 2 82 Tuna, water packed 6 ounces 170 40. 1 80 Beefsteak, broiled 6 ounces 170 38. 6 77 Cottage cheese 1 cup 225 28. 1 56 Cheese pizza 2 slices 128 15. 4 31 Yogurt, low fat 8 ounces 227 11. 9 24 Tofu 1/2 cup 126 10. 1 20 Lentils, cooked 1/2 cup 99 9 18 Skim milk 1 cup 245 8. 4 17 Split peas, cooked 1/2 cup 98 8. 1 16 Whole milk 1 cup 244 8 16 Lentil soup 1 cup 242 7. 8 16 Kidney beans, cooked 1/2 cup 87 7. 6 15 Cheddar cheese 1 ounce 28 7. 1 14 Macaroni, cooked 1 cup 140 6. 8 14

p. 227 a

p. 227 b

p. 228