A COMPARISON OF THE POSITIVE-ION AND NEGATIVE-ION MASS-SPECTRA OF BIOACTIVE PEPTIDES FROM THE DORSAL SECRETION OF THE AUSTRALIAN RED TREE FROG, LITORIA-RUBELLA

The collision-induced tandem mass spectral data for MH(+) and [M - H]( -) ions from six bio-active peptides from Litoria rubella are compared . Backbone cleavages of [M - H](-) ions provide sequencing information for five of the peptides [e.g. Phe Pro Trp Leu (NH2) and pGlu Phe Pro Trp Leu (NH2)] and in these cases, the negative-ion spectra are as in formative as the positive-ion spectra. Side-chain cleavages are also n oted in these spectra. For example, (i) when Trp is present, the loss of C9H7N (129 u) competes with the backbone cleavages, and (ii) the [M -H](-) ion of ne Glu Phe Phe Thr (NH2) undergoes facile side-chain fra gmentation [loss of H2O (from Glu) and MeCHO (from Thr)], but does not form any conventional backbone-cleavage ions.