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

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 (K-i = 4.8 . 10(-10) M) and a somewhat weaker inhibitor of chymotrypsin (K-i = 4.7 . 10(-8) M) and pronase E (K-i = 5.9 . 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.