SynopsisLight-scattering, sedimentation, viscosity, and reducing power measurements have been carried out on a sample of native dextran from Leuemstoc mesenteroides B-512. The results are discueaed in relation to the structure, polydispersity, and branching of the polysaccharide. The effect of different solvents on the behavior of native dextran has been studied. The molecular weight of the dextran remaim unchanged in 'all the solvents used, while the radius of gyration shows a significant increase in some of them (concentrated salts, urea, and glucose solutions); in water-methanol solutions the radius of gyration slightly decreases.Chemical and physicochemical studies reported in the literature' provide a satisfactory picture of the structure of the polysaccharide dextran and of its behavior in solution. However, the exact shape, size, molecular weight distribution, and branching of different samples of native dextran may be uncertain, owing to variabilities in the properties of the polymer even if it is obtained from the same strain of microorganism.2*3 In the course of investigations on the properties of dextran derivatives, it has been therefore necessary to characterize by different physicochemical methods the sample of native dextran used. Moreover, it seemed interesting to study the effect of different solvents on some properties of native dextran. It was hoped that such studies might give additional information on the behavior of the polymer in solution. Also, experiments of this kind are a necessary prerequisite for the interpretation of the effects of the same solvents on the properties of modified dextrans and on the interactions of native and modified dextrans. MATERIAL AND METHODSAll the experiments were carried out on a sample of native dextran synthesized by dextransucrase of Leuconostoc mesenteroides, NRRL B-512(F), P.P. 40-B (supplied by the Northern Regional Research Laboratory of the U.S. Department of Agriculture, Peoria, Ill.).

synopsisThe kinetics of the depolymerization of native dextran in dilute hydrochloric acid a t different temperatures has been followed by measurements of M,, a,,, [ q ] , (Pp)''', and S. The data allow the correlation of the various parameters of the total hydrolyzate a t various degrees of depolymerization. At a first approximation the results conform to a random splitting of a statistical, branched polymer.

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The possibility that C’3 participates in tumor rejection was investigated in DBA/2 mice previously immunized against L1210 leukemia and in Swiss mice previously immunized against Ehrlich’s adenocarcinoma. In both the cases, animals treated with an appropriate dose of cobra venom factor to produce a C’3 depletion for some days after the tumor challenge, developed the neoplasia and had a mortality rate analogous to that of non-immunized animals. Studies on the peritoneal washing cells obtained at different times after the challenge revealed that in C’3 depleted immunized mice IgM are present on lymphocytes, macrophages and tumor cells, as in the immunized controls, but no contact between the cells and no macrophage phagocytosis were observed and the number of tumor cells increased progressively. These findings indicate that C’3 is critically involved in the rejection of the experimental tumors considered.