PRIMARY STRUCTURE AND SPECIFICITY OF A SERINE PROTEINASE-INHIBITOR FROM PAPRIKA (CAPSICUM-ANNUUM) SEEDS

Several fractions demonstrating trypsin inhibitory activity were isola ted from the seeds of the paprika plant (Capsicum annuum). One of the inhibitors, PSI-1.1, was purified to homogeneity and characterised. Th e 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 o f trypsin (K-i = 4.8 . 10(-10) M) and a somewhat weaker inhibitor of c hymotrypsin (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 conditio ns (down to pH 2.0) and to pepsin digestion, presumably due to its fou r disulfide bridges.