The effect of different extraction procedures on two different molecular weight species of serum NSILA and on the carrier protein of small molecular weight NSILA (NSILA-S).

The influence of Dowex-50 adsorption chromatography on the recovery of two different forms of serum NSILA, large and small mol. wt. NSILA, and on the recovery of the binding protein of the small mol. wt. form was studied and compared with another extraction procedure, gel filtration on Sephadex G-50 in 1 M acetic acid. Partially purified NSILA-S is adsorbed to Dowex-50 at pH 6.8. It can be eluted with 20 mM NH4OH and appears unchanged with regard to its biological activity and molecular weight. Adsorption of 125I-labelled NSILA-S to Dowex-50 does not change its binding characteristics to serum. When serum is chromatographed on Sephedex G-50 in 1 M acetic acid, NSILA is obtained in a large and in a small molecular weight form (NSILA-S). After recombination of the small molecular weight NSILA fraction with the "stripped" serum fraction, which contains large mol. wt. NSILA and a specific carrier protein for NSILA-S, re-chromatography of this mixutre on Sephadex G-50 at neutral pH yields NSILA mostly in the void volume. It adsorbs to Dowex-50. After elution from Dowex, acidic gel filtration on Sephadex G-50 results in an elution pattern which is completely different from that of NSILA-S. Adsorption of serum to Dowex-50 results in a dramatic decrease of the NSILA-S binding activity. It is concluded that Dowex-50 adsorption chromatography of serum 1) inactivates most of the serum NSILA-S binding protein 2) leads to the loss of acid dissociable small mol. wt. NSILA (NSILA-S). Therefore, Dowex-50 adsorption chromatography is not suitable for the subsequent determination or further purification of NSILA-S from whole serum.