of experimental error the concentration of silver nitrate in the middle compart-Inent remained unchanged during the electrolysis.Results.--The table lists the cation transference numbers obtained at 25.00 ~ • 0.01~ Solvent Moluli~y t+ Water 0.0500 0.463 Water 0.0498 0.465 Water 0.0497 0.462 Water 0.0497 0.462 Acetone 8.57 X 10 -~ 0.449 Acetone 8.57 X 10 -3 0.445 Discussion.--The average value for the silver ion transference number in water is 0.463 ~ 0.003 (99 % confidence limits). This average is not significantly different at the 10% level of significance ("Students t" test) ~ from the value, 4 0.4664, obtained by the moving boundary method. The two results for dilute solutions of silver nitrate in acetone are included to show that the apparatus yields reasonably precise results for solutions of low conductivity.

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The interaction of two sodium n-alkyl sulfates (C10 and C12) with porcine pancreatic phospholipase A2 and its zymogen was studied by various spectroscopic techniques, equilibrium gel filtration, calorimetry, and photochemically induced dynamic nuclear polarization 1H NMR. At very low concentrations of n-alkyl sulfate [up to 0.07 X critical micelle concentration (cmc)] the enzyme (Mr 14 000) is able to build up a complex with the detergent molecules having a molecular weight of about 90 000. This complex consists of 6 enzyme molecules and about 40 n-alkyl sulfate monomers. The formation of the detergent-protein aggregate occurs in a two-step process: First, two detergent molecules strongly bind to a hydrophobic surface region of the protein, previously called interface recognition site [Pieterson, W. A., Vidal, J. C., Volwerk, J. J., & de Haas, G. H. (1974) Biochemistry 13, 1455-1460]. Subsequently, at higher detergent concentrations suddenly 6 enzyme molecules aggregate, probably including about 30 additional detergent monomers. Although the zymogen of the pancreatic phospholipase A2 seems to form comparable high molecular weight aggregates with these detergents, there are spectroscopic differences, and higher detergent concentrations are required. Moreover, as will be shown in the following paper [Hille, J. D. R., Egmond, M. R., Dijkman, R., van Oort, M. G., Sauve, P., & de Haas, G. H. (1983) Biochemistry (following paper in this issue)], only the phospholipase A2 becomes superactivated in these complexes.

Circular dichroism of human immunoglobulin G and its tryptic digestion fragments Fab(t) and Fc(t) was studied in neutral and acid solutions. In neutral solutions, all the proteins examined showed at least two circular dichroism bands in the far ultraviolet zone: a negative band centered at 217 µ and a positive band at approximately 202 µ. The former indicates the presence of the ß structure. In hydrochloric acid (pH 2.2), the positive band at 202 µ was shifted to a negative band at 200 µ, whereas the negative band at 217 µ was affected very little. At low pH, all the other bands (at 230 to 300 µ) were strongly reduced. The negative ellipticity values at 200 µ in acid (pH 2.2) were different for each protein but the general features of the T X he optical rotatory dispersion of immunoglobulin G has been studied in several laboratories. Analyses by Drude and Moffitt methods have been interpreted to indicate little or no a helix in IgG1 (