Size and Shape of Blood Group A-Substance

Abstract

Kekwick has recently presented data on the size and shape of an A-substance preparation from pseudomucinous ovarian cyst fluid 1 . He obtained a molecular weight of 260000 and an axial ratio of 60/1 from ultracentrifuge and diffusion measurements. For comparison it seems worthwhile to present briefly data obtained on other preparations of A-substance 2 .

Materials. The closely related preparations R18-F10, R19-F1A, and R19-F2A of A-substance from hog gastric mucin were used ( 3 , 4 ).‡ This material is known to be chemically and immunologically inhomogeneous ( 3 , 4 ). The solvent used in all experiments was 0.02 M phosphate buffer at pH 7.1 with sufficient sodium chloride to give an ionic strength of 0.15.

Light scattering. Measurements were made at concentrations between 1.0 and 0.1%. Values of the reciprocal of specific turbidity were plotted against concentration and extrapolated to zero concentration. The molecular weights of R19-F1A and R19-F2A calculated from the values of (C/τ) c=o were 900,000 and 1,100,000 respectively. All samples were centrifuged for 30 minutes at 25,000 times gravity to remove optical haze. The refractive index increment for 5461 Å was 0.14 (concentration expressed as weight fraction).

Diffusion. Free diffusion measurements at 2 concentrations of R18-F10 were made at 1.3 °C in a Neurath cell using a Longsworth scanning optical system. By the height-area method

and by the method of successive analysis

for 5 determinations. Pycnometric measurements gave an apparent specific volume of 0.66 ml/g.

Viscosity. The values of specific viscosity, γ_tsp, divided by volume fraction of solute, θ, at different rates of shear are given in Table I. Measurements were made in an Ostwald-Fenske viscometer at 25°C.

Osmotic Pressure. Four measurements at one and 2% concentration gave the molecular weight of R18-F10 as 220,000 ± 30,000, uncorrected for deviations from ideal behavior.