The characterization of somatomedin A, isolated by microcomputer-controlled chromatography, reveals an apparent identity to insulin-like growth factor 1.
The polypeptide termed somatomedin A (SMA) was isolated from outdated human plasma by a new purification procedure, not using acid ethanol extraction. Fractions containing SMA were monitored by a placenta radioreceptorassay and a radioimmunoassay for SMA. The purification method utilized a microcomputer-controlled chromatography system, yielding both SMA (identified as insulin-like growth factor 1 (IGF-1) or a deamidated derivative) and insulin-like growth factor 2 (IGF-2). The first step of CM-Affigel blue adsorbed at neutral pH the majority of somatomedins detectable by the radioreceptorassay for SMA. Exclusion chromatography on Sephadex G-50 in 0.1 M acetic acid separated this active material from albumin and NaCl. Separation between SMA and IGF-2 was achieved on two different cation-exchange columns, but not in the final high-performance liquid chromatography step. The isoelectric points, determined by chromatofocusing, were 8.0 for SMA and 6.2 for IGF-2. The amino acid compositions of the two isolated peptides were indistinguishable from the known compositions of IGF-1 and IGF-2. Sequence analysis up to position 39 of the peptide with a pI of 6.2 also proved identity with IGF-2 for all positions examined. The peptide with a pI of 8.0, corresponding to SMA, was degraded directly as well as after CNBr cleavage. The results show that it is identical to IGF-1, with the possible exception of acid/amide assignment, which could correspond to a deamidation. If occurring in the native preparation before analysis, it could explain the chromatographic properties and isoelectric point of SMA versus IGF-1 isolated by other techniques.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D003201:Computers; D006801:Humans; D007328:Insulin / Q000032:analysis*; D007335:Insulin-Like Growth Factor II; D007525:Isoelectric Focusing; D008838:Microcomputers; D010455:Peptides / Q000032:analysis*; D011863:Radioimmunoassay; D011869:Radioligand Assay; D013002:Somatomedins / Q000032:analysis*
D000596:Amino Acids; D007328:Insulin; D010455:Peptides; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II