Structural modification of polyfunctional rubratoxin B: effects on mammalian adenosine triphosphatase

Area of Science:

• Biochemistry
• Toxicology
• Enzymology

Background:

• Rubratoxin B is a toxic metabolite produced by Penicillium molds.
• Adenosine triphosphatase (ATPase) enzymes are crucial for cellular energy processes.
• Previous studies indicated rubratoxin B's in vivo inhibition of ATPase preparations.

Purpose of the Study:

• To investigate the in vitro inhibitory effects of rubratoxin B and its analogs on ATPase activity.
• To determine the structure-activity relationship of rubratoxin B in ATPase inhibition.
• To elucidate the role of the intact rubratoxin B molecule in its toxicological effects on ATPase.

Main Methods:

• In vitro enzyme inhibition assays using brain microsomal Na+ - K+ ATPase and mitochondrial Mg++ ATPase.
• Testing of rubratoxin B, rubratoxin A, dihydrorubratoxin A, and dihydrorubratoxin B.
• Comparative analysis of inhibition across different mammalian species (swine, mouse, rat).

Main Results:

• Rubratoxin B significantly inhibited both Na+ - K+ ATPase and Mg++ ATPase with low IC50 values.
• Structural modifications (rubratoxin A, dihydro analogs) markedly reduced ATPase inhibition.
• The order of inhibitory potency was rubratoxin B > dihydrorubratoxin B > rubratoxin A > dihydrorubratoxin A.
• No significant species variation in ATPase inhibition was observed.

Conclusions:

• The intact structure of rubratoxin B is essential for its potent inhibition of ATPase enzymes.
• Chemical alterations to the maleic anhydride ring or conjugated lactone moiety diminish inhibitory activity.
• These findings support the hypothesis that rubratoxin B acts directly on ATPase in vivo.