Substitution of SER 61 → GLY 61 in human apolipoprotein C-II does not alter its activation of lipoprotein lipase

Abstract

Lipoprotein lipase (LpL) activity is enhanced by apolipoprotein C-II (apoC-II), a 79 amino acid residue peptide. The minimal apoC-II sequence required for activation of LpL resides between residues 56–79. To determine the possible role of an acyl-apoC-II intermediate involving Ser 61 in enzyme catalysis, a synthetic peptide of apoC-II containing residues 56–79 was synthesized and compared to the corresponding peptide with serine at position 61 being substituted with glycine. With two different LpL assay systems, both peptides enhanced enzyme activity. Since glycine does not contain a hydroxyl group, these results rule out the possibility that an acyl-apoC-II intermediate with Ser 61 is required for enzyme activation.