Uptake of rat and human α2‐macroglobulin‐trypsin complexes into rat and human cells

Abstract

Uptake of rat and human α₂-macroglobulin-trypsin complexes was measured in rat hepatocytes, rat and human adipocytes and human fibroblasts. Uptake and degradation of ¹²⁵I-labelled rat complex were about one-third of that of the human complex in the various isolated cell types. In rat hepatocytes, the apparent K _m for cell association of the rat complex was about 16 nM as compared to about 6 nM for the human complex. The V _max values were similar, about 1 × 10⁴ molecules · cell⁻¹ · min⁻¹. Thus, rat α₂-macroglobulin (an acute-phase protein) complexed with trypsin follows the same pathways of uptake as the human homologue, although with a somewhat lower affinity for the uptake system.