A new apoprotein has been isolated from delipidated human very low density lipoproteins by Sepharose 6B chromatography in 6 Y guanidine hydrochloride. This water-insoluble protein was noted to be unique to the plasma very low density and chylomicron fractions. This protein was shown to be homogeneous by urea-DEAE-cellulose chromatography, rechromatography in a guanidine-Sepharose system, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and isoelectric focusing. The molecular weight of

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... this apoprotein obtained by guanidine gel filtration, sedimentation equilibrium in guanidine hydrochloride, and by sodium dodecyl sulfate polyacrylamide gel electrophoresis was 33,000. The amino acid content was significantly different from any previously characterized very low density lipoprotein apoprotein, containing relatively more arginine. By the dansylation and cyanate techniques the NH2-terminal amino acid was found to be lysine. Digestion with carboxypeptidase revealed the COOH-terminal sequence to be -Leu-Ser-Ala-COOH.