AbstractThe electrophoretic mobilities (E.P.M.) and pH‐mobility relationships of chick blastoderm cells at successive developmental stages were determined. Mobilities in 0.145MNaCl, pH 7.2, showed a wide spread and decreased from a mean value of 1.63 μ/sec/V/cm in the prestreak blastoderm, to 1.49 in the intermediate streak and 1.34 in the head process stages. Cell surface charge density changes as detected by E.P.M. were observed in all regions of the embryo.pH‐mobility relationship studies showed that two cell populations differing in their approximate isoelectric point appeared at the intermediate streak and head process stages. Neuraminidase treatment indicated that the contribution of sialic acid residues to the negatively charged groups at the cell surfaces is very small at the stages stu
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