The N terminus of human myelin basic protein consists of C2, C4, C6, and C8 alkyl carboxylic acids.

Abstract Peptide 1-21, generated by cyanogen bromide cleavage of each of two highly purified components of human myelin basic protein, components 1 and 8, gave a series of peaks in the fast atom bombardment mass spectra with m/z 2299, 2327, 2355, 2383, and 2411, indicating additions of 42, 70, 98, 126, and 154 atomic mass units respectively with m/z 2327 and 2355 as the dominant species. The pentafluorobenzyl esters prepared from an acid hydrolysate analyzed by negative ion chemical ionization gas chromatography mass spectrometry confirmed that C6, C8, and C10 fatty acids were present. These data demonstrated (i) that the N terminus of a myelin basic protein is not simply acetylated but contains C2, C4, C6, C8, and C10 fatty acids with C4 and C6 as the dominant species, (ii) the two components studied (C-1 and C-8) showed different relative amounts of C2 and C8 in particular, and (iii) human myelin basic protein is the first protein to be reported with a complex N terminus consisting of several alkyl carboxylic acid species.