Mannose 6-phosphate receptors (MPR 300 and MPR 46) from a teleostean fish (trout)

Mannose 6-phosphate receptors (MPRs) are known to occur in mammals, birds, reptiles and amphibians. Here we provide evidence for the presence of two MPRs in fish, the earliest vertebrates. Using phosphomannan-Sepharose affinity chromatography, MPR 300 was purified from liver membrane extract of trout. The purified trout liver MPR 300 showed similar electrophoretic mobility as the goat liver receptor and a pH optimum of 7.0 for binding to phosphomannan. The presence of MPR 46 in fish was shown by metabolically labelling embryonic fish cells (Xiphophorus) and immunoprecipitation with an antibody against the cytoplasmic tail of human MPR 46 (anti-MSC1). This antibody had recently been shown to immunoprecipitate MPR 46 also from reptiles and amphibians.