Apolipoprotein B synthesis: a square lattice model

We have formulated a random walk model for emerging apolipoprotein B interaction with its translocation channel on the surface of the rough endoplasmic reticulum based on the assumption that this interaction is a diffusion-mediated process. From this model, we found that a substantial proportion of mRNA-ribosome complexes was not bound to their translocation channels at any given moment of quasi-steady state. The duration of polypeptide chain elongation was an important determinant of the number of mRNA-ribosome complexes bound to their channels, but it had little net effect on the integrated rate of protein synthesis and translocation. The rates of protein synthesis and translocation for different secretory proteins that were cotranslationally translocated were very similar provided that they had similar mRNA concentration. We conclude that one of the control mechanisms regulating apolipoprotein B production may rely on the properties of translocation channels to determine the fate of newly synthesized apolipoprotein B molecules.