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Eric Niederhoffer SIU-SOM

SSB End of Unit Review. Eric Niederhoffer SIU-SOM. Submitted Questions. Which enzymes are inhibited by elevated NADH versus which steps cause elevated NADH ? Inhibited: Dehydrogenases Elevated: ADH, AlDH Specific inhibitory/activating substrate interactions with PFK1, PFK2

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Eric Niederhoffer SIU-SOM

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  1. SSB End of Unit Review Eric Niederhoffer SIU-SOM

  2. Submitted Questions • Which enzymes are inhibited by elevated NADH versus which steps cause elevated NADH? Inhibited: Dehydrogenases Elevated: ADH, AlDH • Specific inhibitory/activating substrate interactions with PFK1, PFK2 Inhibitory: ATP, citrate Activating: F6P, F26BP, F16BP, NH4+, AMP, Pi • Why F16BP stimulates both PFK1 and PK? Feed-forward activation • Significant and differentiating characteristics of metabolic diseases (examples given in RS) Physical symptoms, metabolites

  3. Peroxisome Cytosol H2O2 NAD+ ER CAT O2 ADH MEOS NADPH Pyrazole H2O P450 NADH Aminotriazole NADP+ NAD+ Mitochondrion AlDH NADH Disulfiram (antabuse) Chlorpropamide (diabetes) Extra-hepatic tissue Oh my! Now what? Cellular Processing EtOH Acetaldehyde Acetate

  4. G6Pase GK G6P F6P F16BPase PFK Ala F16BP Asp PEPCK OAA PEP ALT AST NAD+ NAD+ PK MDH LDH MDH Lactate Pyr Malate OAA NADH NADH NADH PDH β-Ox NADH PC Acetyl CoA FA Malate NAD+ NADH MDH OAA Cit NADH Malate ICit IDH Fum NAD+ NAD+ NADH αKGDH Suc αKG S CoA NADH Pathway Perturbations Glc Cytosol Protein Mitochondrion

  5. Ep AR ATP Citrate AC cAMP ATP G6P PKA Ca2+ PKa F6P PFK-2 PP F26BP Pi IMP AMP NH4+ AMP Pi F16BP PEP PDHP Ca2+ PDHP PDHK Pyr Acetyl-CoA PDH Regulation in Skeletal Muscle Glc Glycolysis PFK-1 Glycogen Glycogenolysis b-Oxidation Fatty acids PK PDH

  6. Glycogen Storage Disease Type VII (Tarui Disease) • Classic, infantile onset, Late onset • Exercise intolerance, fatigue, myoglobinuria • Phosphofructokinase • Tetramer of three subunits (M, L, P) • Muscle/heart/brain - M4; liver/kidneys - L4; erythrocytes - M4, L4, ML3, M2L2, M3L • General symptoms of classic form • Muscle weakness, pronounced following exercise • Fixed limb weakness • Muscle contractures • Jaundice • Joint pain • Laboratory studies • Increased serum creatine kinase levels • No increase in lactic acid levels after exercise • Bilirubin levels may increase • Increased reticulocyte count and reticulocyte distribution width • Myoglobinuria after exercise • Ischemic forearm test - no lactate increase with ammonia increase

  7. Pyruvate Dehydrogenase Complex Deficiency • Neonatal, infantile, childhood onset • Abnormal lactate buildup (mitochondrial disease) • Pyruvate dehydrogenase complex • E1 -  (thiamine dependent) and  subunits, 22 tetramer • E2 - monomer (lipoate dependent) • E3 - dimer (riboflavin dependent) common to KGDH and BCAKDH • X protein - lipoate dependent • Pyruvate dehydrogenase phosphatase • Nonspecific symptoms (especially with stress, illness, high carbohydrate intake) • Severe lethargy, poor feeding, tachypnea • Key feature is gray matter degeneration with foci of necrosis and capillary proliferation in the brainstem (Leigh syndrome) • Infants with less than 15% PDH activity generally die • Developmental nonspecific signs • Mental delays • Psychomotor delays • Growth retardation • Laboratory studies • High blood and cerebrospinal fluid lactate and pyruvate levels • Elevated serum and urine alanine levels • If E2 deficient, elevated serum AAs and hyperammonemia • If E3 deficient, elevated BCAA in serum, KG in serum and urine

  8. Maple Syrup Urine Disease (Branched-Chain -Ketoaciduria) • Classic (early) and late onset (5 clinical phenotypes; classic, intermediate, intermittent, thiamine-responsive, and E3-deficient) • Encephalopathy and progressive neurodegeneration • Branched-chain -ketoacid dehydrogenase complex • E1 -  (thiamine dependent) and  subunits, 22 tetramer • E2 - monomer (lipoate dependent) • E3 - dimer (riboflavin dependent) common to KGDH and PDH • BCKD kinase • BCKD phosphatase • Initial symptoms • Poor feeding, vomiting, poor weight gain, and increasing lethargy • Neurological signs • Alternating muscular hypotonia and hypertonia, dystonia, seizures, encephalopathy • Laboratory studies • Elevated BCAA in serum • Presence of alloisoleucine in serum • Presence of -HIV, lactate, pyruvate, and KG in urine • Treatment • Restriction of BCAA • Supplementation with thiamine

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