TY - JOUR
T1 - Tryptic peptide analysis of the human apolipoprotein E isomorphs
AU - Pereira, L. V.
AU - Dolphin, P. J.
PY - 1982
Y1 - 1982
N2 - The nature of the polypeptide backbone of human apolipoprotein (apo)E present in the very low density lipoprotein (VLDL) of normal and homozygous type III hyperlipoproteinemic patients was investigated by tryptic cleavage fingerprinting and specific chemical modification studies. Apo E from normal subjects was resolved on polyacrylamide isoelectric focussing gels into five bands (apo E-I', E-I, E-II, E-III, and E-IV), whereas apo E from type III patients was resolved into three bands (apo E-I3', E-I3. and E-II3). The apo E isoforms, contained within unstained polyacrylamide gel slices, were washed to remove ampholytes, desialylated, and digested with L-1-tosylamido-2-phenylchloromethyl ketone treated trypsin. Autoradiography of 125I- labelled tryptic apo E peptides showed complete identity between all isoforms from normal subjects. High performance liquid chromatographic (HPLC) analysis showed that complete peptide identity exists between apo E-I', E-I, and E-II and between apo E-I3', E-I3, and E-II3. Distinct HPLC peptide profiles were found for apo E-II, E-III, E-IV, and E-II3. These resolved peak differences were reproducible between runs, between digests, and between apo E isolations, suggesting that the distinct profiles were neither a result of artifacts nor of contamination. Specific chemical modification studies revealed that human apo E isomorphism is due, in part, to differences in arginine and cysteine residues but not to lysine residues. These findings indicate that human apo E isomorphism results from differences in the primary amino acid sequence of the individual isoforms in addition to charged carbohydrate heterogeneity. Furthermore, the apo E isomorphic profile observed in homozygous type III hyperlipoproteinemic patients reflects both a deficiency of apo E-III and E-IV and the presence of the altered apo E-II isoprotein (apo E-II3).
AB - The nature of the polypeptide backbone of human apolipoprotein (apo)E present in the very low density lipoprotein (VLDL) of normal and homozygous type III hyperlipoproteinemic patients was investigated by tryptic cleavage fingerprinting and specific chemical modification studies. Apo E from normal subjects was resolved on polyacrylamide isoelectric focussing gels into five bands (apo E-I', E-I, E-II, E-III, and E-IV), whereas apo E from type III patients was resolved into three bands (apo E-I3', E-I3. and E-II3). The apo E isoforms, contained within unstained polyacrylamide gel slices, were washed to remove ampholytes, desialylated, and digested with L-1-tosylamido-2-phenylchloromethyl ketone treated trypsin. Autoradiography of 125I- labelled tryptic apo E peptides showed complete identity between all isoforms from normal subjects. High performance liquid chromatographic (HPLC) analysis showed that complete peptide identity exists between apo E-I', E-I, and E-II and between apo E-I3', E-I3, and E-II3. Distinct HPLC peptide profiles were found for apo E-II, E-III, E-IV, and E-II3. These resolved peak differences were reproducible between runs, between digests, and between apo E isolations, suggesting that the distinct profiles were neither a result of artifacts nor of contamination. Specific chemical modification studies revealed that human apo E isomorphism is due, in part, to differences in arginine and cysteine residues but not to lysine residues. These findings indicate that human apo E isomorphism results from differences in the primary amino acid sequence of the individual isoforms in addition to charged carbohydrate heterogeneity. Furthermore, the apo E isomorphic profile observed in homozygous type III hyperlipoproteinemic patients reflects both a deficiency of apo E-III and E-IV and the presence of the altered apo E-II isoprotein (apo E-II3).
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U2 - 10.1139/o82-133
DO - 10.1139/o82-133
M3 - Article
C2 - 7172090
AN - SCOPUS:0020362824
SN - 0008-4018
VL - 60
SP - 1032
EP - 1042
JO - Canadian Journal of Biochemistry
JF - Canadian Journal of Biochemistry
IS - 11
ER -