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Imino group of PROLINE creates kinks and bends.
It is Found in: hair,muscle,skin,collagen,cartilage.
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In PKU, Phenylalanine competitively inhibits
tyrosinase and, together with the reduced availability of tyrosine, a melanin
precursor, results in the hypopigmentation of hair and skin.
A defect in histidine ammonia
lysase occurs in histidinemia with hearing and speech deficits;
a defect in cystathionase occurs
in cystathioninuria;
a defect in sarcosine
dehydrogenase occurs in sarcosinemia
defect in 4-hydroxyphenylpyruvate
dioxygenase occurs in tyrosinemia type III.
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Propionic acidemia results from a block in propionyl CoA
carboxylase (PCC), which converts propionic to methylmalonic acid.
Excess propionic acid in the blood produces metabolic acidosis with a decreased bicarbonate
and increased anion gap (the serum cations sodium plus potassium minus the
serum anions chloride plus bicarbonate). The usual values of sodium (~140
meq/L) plus potassium (~4 meq/L) minus those for chloride (~105 meq/L) plus
bicarbonate (~20 meq/L) thus yield a normal anion gap of ~20 meq/L. A low
bicarbonate of 6 to 8 meq/L yields an elevated gap of 32 to 34 meq/L, a
"gap" of negative charge that is supplied by the hidden anion (propionate
in propionic acidemia). Biotin is a cofactor for PCC and its deficiency
causes some types of propionic acidemia. Vitamin B12 deficiency can cause
methylmalonic aciduria because vitamin B12 is a cofactor for methylmalonyl
coenzyme A mutase. Glycine is secondarily elevated in propionic acidemia, but
no defect of glycine catabolism is present.
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