Studies on the structure of lecithin: Cholesterol acyltransferase (LCAT)-comparisons of the active site region and secondary structure of the human and the porcine enzymes

1. 1. Chemical modification of essential serine, histidine and cysteine residues of porcine LCAT were accompanied by loss of enzymatic activity. 2. 2. Modification of cysteine with DTNB inactivated the enzyme which could not be reactivated by KCN suggesting direct involvement of the cysteine residue(s) in catalysis. 3. 3. About half of the primary structure of the procine enzyme was determined. 4. 4. Respective regions of the human and porcine LCAT are highly homologous; especially, the amino-terminus and the region surrounding the DFP-labeled serine residues. 5. 5. The observed primary structure differences represent amino acid substitution that are projected to induce significant changes in secondary structure.