The amino acid sequences of two peptide protease inhibitors (Marinostatins C-1 and C-2) were determined by Edman-degradation. The amino acid sequence of C-1 and C-2 were Phe-Ala-Thr-Met-Arg-Tyr-Pro-Ser-Asp-Asp-Ser-Glu and Gln-Pro-Phe-Ala-Thr-Met-Arg-Tyr-Pro-Ser-Asp-Asp-Ser-Glu, respectively. C-1 and C-2 were identical except for differences in their N-terminal regions, suggesting, that C-1 might be derived from C-2 with deletion of two N-terminal amino acids by proteolytic removal of this region.
From the amino acid sequence analysis, the molecular weight of C-1 was calculated to be 1, 417.5 and that of C-2 to be 1, 643.8. Field mass spectral analysis of C-1 and C-2 gave parent peaks corresponding to the molecular weights of 1, 381.5 and 1, 589.5, respectively. As inhibitory activity is lost in an alkaline pH range (pH>10), it is suggested that 2 or 3 ester linkages might exist in the peptide molecules, which play a part in the inhibitory activity of Marinostatins.