| Abstract: | Apolipoprotein (apo) C-III isoforms from a patient with a mutant apo C-III and from controls were isolated to homogeneity by isoelectric focusing and subjected to proteolytic digestion. The peptides obtained were separated by reversed-phase high-performance liquid chromatography, and their molecular masses were determined by time-of-flight secondary ion mass spectrometry. Molecular masses of peptides derived from apo C-III0, C-III1 and C-III2 were indistinguishable from control preparations, whereas the mutant apo C-III contained a COOH-terminal, carbohydrate-containing peptide with an abnormal retention time in high-performance liquid chromatography and a molecular mass higher by 291 daltons owing to oversialation at position 74 of the amino acid sequence (apo C-III3). |
