Endocytes and breakdown of ribonuclease oligomers by sinusoidal rat liver cells in vivo: II. Effect of charge

Experiments presented in this paper suggest that sinusoidal rat liver cells recognize basic on proteins and that this recognition results in endocytosis of the proteins. Evidence for involvement of basic groups was obtained in two ways.Firstly, we changedd the opsitively charged amino groups of the cross-linked ribonuclease molecules to neutral or negative by acetylation or succinylation, respectively. The modified proteins did not contain easily reducible disulfide bonds and they were not very sensitive to endoproteases, suggesting that they were not denatured by the acetylation procedures. Acetylation and succinylation reduced uptake of the injected cross-linked ribonuclease derivatives by liver and spleen and abolsihed their rapid clearance from plasma. In nephrectomized rats about 75% of the polymer, 36% of the acetylated polumer and 32% of the succinylated polumer were endocytosed by liver after 6 h. For the dimer fraction these values were 59%, 23% and 27%, respectively. Autoradiography and subcellular fractionation of liver 30 min post-injection localized the acetylated polumer in the lysosomal/microsomal fraction of sinusoidal liver cessls, probably endothelial cells.Secondly, a positive correlation was found between binding of a number of ribonuclease derivatives of the cation exchanges SP-Sephadex G-25 and the rate of endocytosis by sinusoidal liver cells.