xP2, a new member of the P-domain peptide family of potential growth factors, is synthesized in Xenopus laevis skin

Similarly to epidermal growth factor (EGF) and EGF-like repeats, the "P-domain" represents a cysteine-rich module that has been detected in the past in a variety of polypeptides, as well as in high molecular weight proteins. Here, a precursor for a secretory polypeptide (xP2) is characterized that consists of two P-domains. xP2 has been discovered in Xenopus laevis with the help of the polymerase chain reaction. In contrast to all other P-domain peptides, it is synthesized in the skin but not in the stomach or the pancreas. By this and other criteria, it cannot be considered simply as the X. laevis homologue of recently described P-domain peptides, viz. the spasmolytic polypeptides (PSP/hSP/mSP). Furthermore, a polyclonal antiserum was generated against the deduced C-terminal end of xP2. Due to its immunoreactivity with granular glands, as well as with the epidermis, the possibility of a growth factor activity for xP2 in the germinal layer is discussed.