Page 121 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM SECTION II 77

Pyruvate Causes a buildup of pyruvate that gets shunted to lactate (via LDH) and alanine (via ALT).
dehydrogenase X-linked.
complex deficiency
FINDINGS Neurologic defects, lactic acidosis,  serum alanine starting in infancy.
TREATMENT  intake of ketogenic nutrients (eg, high fat content or  lysine and leucine).

Pyruvate metabolism Functions of different pyruvate metabolic
pathways (and their associated cofactors):
Glucose Alanine aminotransferase (B 6 ): alanine
carries amino groups to the liver from
muscle
Pyruvate Pyruvate carboxylase (biotin): oxaloacetate
ALT can replenish TCA cycle or be used in
LDH
gluconeogenesis
Alanine NADH
Cahill cycle Cytosol + H + NAD + Lactate Pyruvate dehydrogenase (B 1 , B 2 , B 3 , B 5 ,
Mitochondria Cori cycle lipoic acid): transition from glycolysis to
PC
NAD + PDH the TCA cycle
CO + ATP
2 Lactic acid dehydrogenase (B 3 ): end of
CO 2 anaerobic glycolysis (major pathway in
NADH RBCs, WBCs, kidney medulla, lens,
Oxaloacetate + H + testes, and cornea)
Acetyl-CoA

TCA cycle
Pyruvate (3C) Also called Krebs cycle. Pyruvate Ž acetyl-CoA
ATP produces 1 NADH, 1 CO 2 .
*
PDH Acetyl-CoA The TCA cycle produces 3 NADH, 1 FADH 2 ,
NADH 2 CO 2 , 1 GTP per acetyl-CoA = 10 ATP/
Acetyl-CoA (2C) acetyl-CoA (2× everything per glucose). TCA
ATP
cycle reactions occur in the mitochondria.
Oxalo- Citrate synthase
NADH acetate * Citrate (6C) α-ketoglutarate dehydrogenase complex
(4C) cis-Aconitate requires the same cofactors as the pyruvate
Malate (4C) Isocitrate (6C) dehydrogenase complex (vitamins B 1 , B 2 , B 3 ,
B 5 , lipoic acid).
* CO + NADH Citrate Is Krebs’ Starting Substrate For Making
2
Fumarate (4C) Isocitrate ATP
dehydrogenase NADH Oxaloacetate.
ADP
FADH 2 α-KG (5C)
Succinate (4C) α-KG dehydrogenase CO + NADH
*
2
GTP + CoA
Succinyl- Succinyl-CoA
CoA (4C) NADH
ATP
* Enzymes are irreversible

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