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The present experimental study of the conductance and transference of alkali salts of bovine serum albumin under varying conditions of charge and salt concentration aims at a quantitative interpretation of electrophoresis. Special attention is paid to the range of low and zero salt content. For salt-free albuminates at low protein charge, the contribution of the charge fluctuations of the protein to the current transport through the solution cannot be neglected. The electrophoretic mobility of the protein appears to be independent of the nature of the alkali ion and increases with the charge, whereas the counterion mobility decreases with increasing protein charge. This lowering increases in the order lithium, sodium, potassium, in agreement with theoretical expectations concerning the relaxation of the ion cloud. Dilution of salt-free albuminates strongly increases the equivalent conductance of both the protein and its counterions as a result of a gradual decrease of the electrical retardations, viz., the electrophoretic and relaxation effect. Albuminates, diaIyzed against dilute salt solutions, reveal a pronounced dependence of the colloid mobility on the protein concentration. In albuminates of constant charge and alkali ion concentration, the protein mobility was measured for different ratios of the albuminate-ion and chloride-ion concentrations. In these mixtures the equivalent conductance of the protein was found to be constant. A theoretical treatment of these data will be given in the next paper.

SynopsisThis paper describes a theoretical and experimental analysis of the binding of magnesium ions to yeast ribosomes. I n the theoretical considerations the interactions between charges located on a macroion are included. I n the calciilations these ititeractions result in a term, in which both the charge and the radius of the macroion are accounted for. I t appears that on dissociation of the ribosomes both the charge and the radius change, biit in such a way, that the t,erm, which accounts for the electrostatic interactions, remains constant. As a c~iiseqiience the dissociation can be neglected i n the analyses of the binding experiments. Our experiments iiidicate that two binding reactions between ribosomes and magnesium ions occur. The endpoints of these react ions correspond to aboiit 0.40 arid 1 .O eytiivalent magnesium per ribosomal phosphate, respectively.The experimental results indicate that the effect of monovalent rations ('an be explained as a piire ionic strength eftect , thoiigh the binding of monovalent catiotis coiild not be excluded ('om-pletely.The p K values are about 3.8 and 2.2, respectively.

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It is shown how the relaxation effect can be determined from transference data on the same colloidal particle with different counterions. The electrophoretic retardation is calculated for spheres with overlapping double layers. The relation between charge and potential distribution is also developed for this case. The theory is applied to transference and electrophoresis data of solutions of bovine serum albumin. Agreement is very good for low charge of the albumin, but less good for charges of 10 or more elementary charges per molecule. The difference is (at least in part) due to the use of the Debye-Huckel approximation. In the range of charges (up to 27 elementary charges per molecule) and concentrations (up to 5 %) used, the electrophoretic retardation is much larger than the relaxation effect, which hardly surpasses 20 % of the total retardation.