Immunoreactive forms of pancreatic stone protein in six mammalian species

Secretory forms of the pancreatic stone protein (PSP S, Mr 17, 500-22,000) have been purified from human pancreatic juice. PSP S are inhibitors of CaCO3 crystal growth. The presence of similar proteins in bovine, canine, monkey, porcine, and rat pancreatic secretion was investigated in terms of biological role and immunological relationship. Pancreatic proteins were analyzed by electrophoretic separation and by subsequent immunoblotting with a rabbit polyclonal antibody against human PSP. A single immunoreactive form was detected in dog, pig, and rat (Mr 17,000), and two distinct immunoreactive forms were observed in cow and monkey (Mr 15,000 and 17,000). Inhibition of CaCO3 crystal growth was demonstrated in dog and rat. Further kinetic studies of the inhibition process in the rat showed that PSP S binds to the crystal surface according to a Langmuir adsorption isotherm with a dissociation constant (Kd) of 1.5 x 10(-6) M. These results suggest that proteins homologous to human PSP S are present in other mammalian species and may act as stabilizers of Ca(2+)-supersaturated pancreatic juice.