Therapeutic use of the SMR1 protein, the SMR1 maturation products, specifically the QHNPR pentapeptide as well as its biologically active derivatives

A method for determining the affinity of a ligand for a receptor of a XQHNPR peptide (SEQ ID NOS:1-7 and 12), comprising the steps of:

• a) preparing a confluent cell culture, organ specimen or tissue sample expressing a receptor of an XQHNPR peptide (SEQ ID NOS:1-7 and 12);
• b) adding a candidate molecule that has been previously labeled with a radioactive or a nonradioactive label to a cell culture, organ specimen or tissue sample said culture, specimen or sample are cells involved in mineral ion balance;
• c) incubating said cell culture, organ specimen or tissue sample in the presence of said labeled candidate molecule for a time sufficient for specific binding to take place between said cell culture, organ specimen or tissue sample and said labeled candidate molecule in the presence and in the absence of unlabeled XQHNPR peptide (SEQ ID NOS:1-7 and 12);
• d) quantifying the label specifically bound to said cell culture, organ specimen or tissue sample in the absence of unlabeled XQHNPR peptide (SEQ ID NOS:1-7 and 12);
• e) quantifying the label specifically bound to said cell culture, organ specimen or tissue sample in the presence of unlabeled XQHNPR peptide (SEQ ID NOS:1-7 and 12);
• and
• f) calculating the affinity based on the amount of label specifically bound in d) and e).