Part 5.pdf

Enzymes for AA Synthesis Essential AAs  59 enzymes total 59 enzymes required to synthesize the 9 essential aa   Expensive to synthesize ?survival advantage to be able to rely on diet Non-Essential AAs  17 enzymes   essential implies important and the nonessential are less important if th...

Enzymes for AA Synthesis Essential AAs  59 enzymes total 59 enzymes required to synthesize the 9 essential aa   Expensive to synthesize ?survival advantage to be able to rely on diet Non-Essential AAs  17 enzymes   essential implies important and the nonessential are less important if theory that it’s an advantage to be able to rely on diet Easy to synthesize ?survival advantage to maintain capacity to theory says that the nonsynthesize this essential ones are more important bc we need it to survive  Are they more important? Dispensable AAs Intake De novo synthesis Special Products Synthesis Free AA Pool Feces Urinary Nitrogen Breakdown CO2, H2O Body Protein label difficult to do in humans can take blood samples: plasma proteins time Precursor-product relationship Plasma Proteins Diet Precursor Pool Glutathione Special products Tracer Some proteins are synthesized really rapidly and some slowly like actin and myosin in muscle can do it also by a tracer that is infused and mixes in the pool and we measure the synthesis of different proteins for different special products by looking at the constant labeling in the precursor pool and we measure over several hours the incorporation of the label in the individual proteins Enzymes Transporters…. Special Products Reeds 2000 Synthesis of dispensable AAs  High flux rates High proportion from de novo synthesis Synthesis accounts for up to 8% of basal metabolic rate Ultimate precursor is glucose of the flux comes      Except for tyrosine For cysteine – only the S is from methionine Cysteine Methionine demethylation Homocysteine Serine Cystathionine comes from glucose Cysteine Classical sulphur AAs Kinetic view of sulphur AAs Relevant for dietary requirement of these 2 sulphur containing aa: both can be used for protein synthesis and both are necessary in the diet (DRI is for cysteine + methionine bc if cysteine is low in the diet, there’s going to be more shunting of HCY) All these B vitamins are important in aa catabolism and energy metabolism vitamin B6 folate: B12 methyl group transfers FAD: flavin —> riboflavin —> B2 NAD: niacin —> B3 important in transamination reaction See Fig 34.3 Issues in sulphur AA metabolism         Methylation reactions Vitamins Homocysteine Liver function Premature infants Intravenous feeding Taurine Glutathione can be used for DNA synthesis and modification vitamin deficiency: B6 requires healthy liver somebody having liver failure can really impact sulphur aa metabolism producing cysteine —> not stable product of cysteine important for premature babies made of 3 dispensable aa Glutathione (GSH)    γ-glutamyl-cysteinyl-glycine intracellular protection against oxidative stress antioxidant       conjugation with electrophiles removal of reactive oxygen species glutathionylation of proteins proteins, lipid membranes, DNA immune system function erythrocyte function each cell in the body needs to do it —> quite expensive Glutathione depletion correcting by: additional protein Nutritional Status   short term fasting protein deficiency Synthesis < Inflammation/ Infection  burns  AIDS Consumption Supplements?  Glutathione - no very expensive aa