Two isoforms of NP24: a thaumatin-like protein in tomato fruit.

Two isoforms (I and II) of the thaumatin-like protein NP24 have been discovered in extracts of tomato fruit. NP24 I increased ca 8-fold during ripening of tomato fruit, whereas NP24 II increased slightly as the fruit began to change colour and them remained constant. Both proteins were purified to homogeneity and one of them, NP24 I, was obtained in crystalline form. The proteins are similar except for differences in binding to cation exchangers and in two amino acids of the N-terminal amino acid sequences. The NP24s were tested as growth inhibitors of six different fungi and found to differ in effectiveness, but both proteins were most effective on Phomo betae and Verticillium dahliae. These proteins may be involved in disease resistance in tomatoes, but the increase in NP24 I during ripening suggests a possible role in fruit development and ripening.