Primary structure and specificity of a serine proteinase inhibitor from paprika (Capsicum annuum) seeds

Abstract

Several fractions demonstrating trypsin inhibitory activity were isolated from the seeds of the paprika plant (Capsicum annuum). One of the inhibitors, PSI-1.1, was purified to homogeneity and characterised. The mature form of PSI-1.1 has a molecular mass of 6053 Da and consists of 55 amino acids in a sequence showing over 80% identity with members of the inhibitors of potato-2 family. PSI-1.1 is a potent inhibitor of trypsin (Ki = 4.8 x 10(-10) M) and a somewhat weaker inhibitor of chymotrypsin (Ki = 4.7 x 10(-8) M) and pronase E (Ki = 5.9 x 10(-8) M). PSI-1.1 is resistant to heat up to 85 degrees C, to acidic conditions (down to pH 2.0) and to pepsin digestion, presumably due to its four disulfide bridges.