Stabilization of the C-Terminal Part of Pig and Horse Colipase by Carboxypeptidase and Trypsin Inhibitors

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Abstract
Pig and horse colipases have been purified by a common procedure using trypsin and carboxypeptidase inhibitors as stabilizers. Two forms of pig colipase were identified: a predominant A1 form with about 103–105 residues, and a minor slightly degraded A2 form in which the last two C-terminal residues, Asp and Ser, were lacking. This type of degradation is considerably slowed down by carboxypeptidase inhibitors. A total of four forms of the horse cofactor were characterized: two (A1 and B1) were probably isocolipases which differed by only a few substitutions. Both contained the same number of residues (about 96), an N-terminal valine and an Arg-Ser-Glu-(Glx)1,2-Arg C-terminal sequence. A2 and B2 were slightly degraded forms probably resulting from tryptic cleavage of the Arg-Ser bond in the above sequence. The presence of methioriine in the horse cofactor allowed fragmentation by cyanogen bromide. The C-terminal fragment was composed of 16 or 17 residues and contained no histidine. The single histidine of horse B1 was found in the intermediary fragment between Met-18 and Met-(n-16) or Met-(n-I7). These data show that the C-terminal parts of both pig and horse colipases are still more exposed to proteolytic degradations than the N-terminal parts. Preliminary attempts to crystallize B1 were carried out.