Peptidase activities and free glutamate production in ripening Micro-Tom fruits

AUGUSTO SORREQUIETA, SILVANA B. BOGGIO AND ESTELA M. VALLE

Manuscrito finalizado

Año: 2008

In tomato (Solanumlycopersicum), free L-glutamate increases dramatically  during fruit ripening in all the cultivated varieties tested so far becoming the most abundant amino acid of ripe fruits, which is in contrast to the tomato wild species. Increased activities of peptidases during tomato fruit ripening are documented, suggesting that glutamate-containing peptides could be the source of free glutamate. In this paper we examined several peptidase activities of pericarp of mature Micro-Tom fruits during ripening. As substrates, we tested endogenous proteins and exogenous molecules such as azocasein and polyglutamate (PGA). In addition, the glutamate liberation after the peptidase activities of pericarp extracts and the [5-l-glutamyl]-peptide:amino acid 5-glutamyl transferase; (EC 2.3.2.2) (g-GTase) activity were monitored in fruit extracts. Results showed that acidic peptidase activities did not contribute to increase free glutamate level from endogenous protein. However, PGA was almost completely hydrolyzed by fruit extracts of all ripening stages.  The higher g-GTase activity observed in mature green fruit did not account for the lower glutamate level in green fruit pericarp. Nevertheless, red fruit still contained enough g-GTase activity to sustain glutamate liberation. In summary, different peptidase activities were clearly present in ripening Micro-Tom but they lack the endogenous substrates to contribute to increase the glutamate level during ripening in mature fruits.