Effect of Pentacyclic Guanidine Alkaloids from the Sponge on Activity of α-Glycosidases from Marine Bacteria.

The effect of monanchomycalin B, monanhocicidin A, and normonanhocidin A isolated from the Northwest Pacific sample of the sponge was investigated on the activity of α-galactosidase from the marine γ-proteobacterium sp. KMM 701 (α-PsGal), and α--acetylgalactosaminidase from the marine bacterium KMM 426 (α-NaGa). All compounds are slow-binding irreversible inhibitors of α-PsGal, but have no effect on α-NaGa. A competitive inhibitor d-galactose protects α-PsGal against the inactivation. The inactivation rate () and equilibrium inhibition () constants of monanchomycalin B, monanchocidin A, and normonanchocidin A were 0.166 ± 0.029 min and 7.70 ± 0.62 μM, 0.08 ± 0.003 min and 15.08 ± 1.60 μM, 0.026 ± 0.000 min, and 4.15 ± 0.01 μM, respectively. The 2D-diagrams of α-PsGal complexes with the guanidine alkaloids were constructed with "vessel" and "anchor" parts of the compounds. Two alkaloid binding sites on the molecule of α-PsGal are shown. Carboxyl groups of the catalytic residues Asp451 and Asp516 of the α-PsGal active site interact with amino groups of "anchor" parts of the guanidine alkaloid molecules.