Interaction of Cytotoxic Bicyclic Peptides, Theonellamides A and F, with Glutamate Dehydrogenase and 17beta-Hydroxysteroid Dehydrogenase IV.

Theonellamide A, a bicyclic peptide isolated from a Theonella sponge, was fixed on hydrazide-containing gel beads and screened for its binding proteins from rabbit liver tissues. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that two major proteins of 80 kDa and 55 kDa interacted with theonellamide A. The interaction between theonellamide A and two proteins was confirmed by competition experiments in which these two proteins failed to bind to theonellamide A-conjugated gel beads in the presence of theonellamide A or F. Amino-terminal amino acid sequence analysis of peptide fragments derived from the binding proteins by lysylendopeptidase digestion demonstrated that the 80-kDa and 55-kDa proteins were 17beta-hydroxysteroid dehydrogenase IV and glutamate dehydrogenase, respectively. In an in vitro assay system, amination of alpha-ketoglutarate by glutamate dehydrogenase was activated with theonellamide F, although this effect was weaker than that with adenosine diphosphate, a well-known activator.