Proteins

·         Imino group of PROLINE creates kinks and bends.

It is Found in: hair,muscle,skin,collagen,cartilage.

·         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.

·         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.