Isoelectric focusing of long-acting thyroid stimulator immunoglobulin G.

Abstract

Isoelectric focusing of long-acting thyroid stimulator immunoglobulin G [LATS-IgG] was used to determine the distribution of LATS activity among IgGs of various isoelectric points and to determine if isoelectric focusing techniques might yield LATS-IgG of increased biologic activity. LATS-IgG prepared from 16 LATS-positive sera was fractionated by isoelectric focusing [72 hr, 1200 V] using a 1% Ampholine solution, pH range 7.0 to 10.0. On the basis of absorbance at 280 nm, the effluent was gathered into 8 fractions. The 8 LATS-IgG subfractions and the parent IgG were tested in the same mouse bioassay. Following each of the 16 isoelectric focusing runs, maximal LATS activity was confined to one [6 instances] or two [10 instances] IgG subfractions [peak pi 8.99 ± 0.08 and 8.78 ± 0.09, respectively], with a 4- to 7-fold increase in LATS activity per mg protein compared to the parent IgG. However, of 12 LATS-negative Graves' disease IgGs submitted to isoelectric focusing, none of the IgG subfractions so deriv...