PURIFICATION AND SEQUENCING OF A RAT INTESTINAL 22 AMINO-ACID C-TERMINAL CCK FRAGMENT

Fractionation of Sephadex G50 gel of methanol extracts of rat intestine revealed 2 molecular forms of cholecystokinin (CCK) of about equal immunopotency: 1 form has an elution volume between CCK33 and CCK12; the other elutes in the salt region as does authentic CCK8. Purification and sequencing demonstrated that the smaller molecular form is CCK8 with a sequence identical to the pork and sheep CCK8''s that was previously sequenced. Purification and sequencing of the larger molecular form reveals that it is a 22 amino acid C-terminal CCK fragment identical with pig CCK22 except that glycine instead of serine is present at the 19th residue from the C-terminus. This sequence is consistent with that predicted by cloned c[complementary]DNA encoding preprocholecystokinin from a rat medullary thyroid carcinoma. CCK22 was not previously reported to be a prominent molecular form in either pig or dog intestines.