Mass spectral study of polymorphism of the apolipoproteins of very low density lipoprotein

New isoforms of apolipoprotein (apo)C-I and apoG-III have been detected in delipidated fractions from very low density lipoprotein (VLDL) using matrix -assisted laser desorption (MALDI) and electrospray ionization (ESI) mass s pectrometry (MS). The cleavage sites of truncated apoC-III isoforms have al so been identified. The VLDL fractions were isolated by fixed-angle single- spin ultracentrifugation using a self-generating sucrose density gradient a nd delipidated using a newly developed C18 solid phase extraction protocol. Fifteen apoC isoforms and apoE were identified in the MALDI spectra and th e existence of the more abundant species was verified by ESI-MS, The relati ve intensities of the apoCs are closely correlated in three normolipidemic subjects. A fourth subject with type V hyperlipidemia exhibited an elevated apoC-III level and a suppressed level of the newly discovered truncated ap oC-I isoform. ApoC-II, was found to be particularly sensitive to in vitro o xidation, The dynamic range and specificity of the MALDI assay shows that t he complete apoC isoform profile and apoE phenotype can be obtained in a si ngle measurement from the delipidated VLDL fraction.-Bondarenko, P. V., S. L. Cockrill, L. K. Watkins, I. D. Cruzado, and R. D. Macfarlane. Mass spect ral study of polymorphism of the apolipoproteins of very low density lipopr otein.