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Flashcards in amino acid metabolism Deck (11):

Phenylketonuria: what is missing? labs?

decr. pheynlalanine hydroxylase or decr. tetrahydrobiopterin cofactor (malignant PKU). tyrosine becomes essential. incr. Phe causes excess phenylketones in the urine.


findings of PKU; tx

intellecutal disability, growth retardation, seizures, fair skin eczema, musty odor (this is a disorder of aromatic aa metab). treat wti h decr. phe and incr. tyr in diet. avoid aspartame


what is maternal PKU

lack of proper dietary therapy during pregnancy. findings in infant: microcephaly, intellectual disability, growth retardation, congenital heart defects


PKU screening

2-3 days after birth. levels normal at birth b/c of maternal enzyme during fetal life



congenital deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumate. autosomal recessive. benign. find a build up of homogentisic acid. see dark CT, brwon pigmented sclera, urine turns black on prolonged exposure to air, and may have bad arthralgias (homogentisic acid toxic to cartilage)


What enzymes may be deficient in homocystinuria?

cystathione synthase deficiency, decr. affinity of cystathione synthase for pyridoxal phosphate (B6), or homocystein methyltransferase deficiency. all cause excess homocystein.
(recall that homocystein can go to methionine via homocystein methytransferase, or to cystathione via cystathione synthase. that rxn requires B6)


findings for homocystinuria

incr. homocysteine in urine, intellectual diability, osteoporosis, tall stature, kyphosis, lens subluxation, thrombosis, and atherosclerosis (stroke and MI)


cystinuria: what is the defect? manifestation?

defect of renal PCT and intestinal amino acid transporter for cystein, ornithine, lysine, and argining. can lead to precipitation of cystine stones (hexogonal). autosomal recessive.


cystinuria: dx and tx

urinary cyanide nitroprusside test. give urinary alkalinization (potssium citrate, acetazolamide) and chelating agents to incr. the solubility of cystine stones. good hydration


maple syrup urine disease

blocks degradation of branched amino acids (isoleucine, leucine, valine) d/t decr. alpha hetoacid dehydrogenase (B1). causes incr. alpha-ketoacids in the blood, esp. those of leucine.


manifestations of maple syrup urine disease. tx

CNS defects, intellectual disability, death. tx: limit isoleucine, leucine, and valine, and supplement thiamine.