Purification from human cerebrospinal fluid of insulin-like growth factor binding proteins (IGFBPs). Isolation of IGFBP-2, an altered form of IGFBP-3 and a new IGFBP species.

Cerebrospinal fluid insulin-like growth factor binding proteins (CSF IGFBPs) characteristically have a preferential affinity for IGF-II, which is largely accounted for by a 32-30 kDa IGFBP(Ka = 10(11) M-1) previously purified from human CSF, with an N-terminal sequence unlike any other IGFBP identified at the time. We have now used procedure (including ammonium sulphate precipitation, acidic gel filtration, affinity chromatography and reverse phase chromatography) and purified three further IGFBPs to homogeneity from child CSF. Apart from the 32-30-kDa form, the predominant IGFBP in CSF is a 34-kDa form (non-reduced in SDS-polyacrylamide gel electrophoresis). Like the 32-30-kDa IGFBP, it has a preferential affinity for IGF-II (Ka = 2 x 10(10) M-1). Its N-terminus, Phe-Arg-(/)-Pro-Pro-(/)-Thr-Pro-Glu-Arg-Arg-(/)-Gly-Pro-Pro-Pro-Val, corresponds to that deduced for IGFBP-2, except for the first three residues which were not found in the CSF IGFBP. Another form, of 30 kDa, has an N-terminus identical to IGFBP-3's over the first 18 residues determined and seems to be an altered form of IGFBP-3. A third minor species, of 22 kDa, with a preferential affinity for IGF-II similar to that of the 34-kDa IGFBP, has an N-terminal sequence, (/)-(/)-Asp-Ser-Phe-Val-Pro-(/)-Glu-Pro-Ser-Asp-Glu-Lys-Ala-Leu-Ser-(/)- (/)-Pro, which bears some analogy with those of other known human IGFBPs, particularly IGFBP-3 (7 homologous residues), and appears to be related to, but distinct from, other IGFBP species.