Incorporation of labeled small molecules into rubratoxin

A sterile glucose-mineral salts broth was inoculated with conidia of Penicillium rubrum P-13 and P-3290. Radiolabeled compounds were added to some cultures, these being incubated quiescently at 28° C for 14 days. Other stationary cultures were grown for 21 days, received labeled compounds, and were then grown for 5 more days. The remaining cultures were inoculated with 72-h-old mycelial pellets, received labeled materials and were incubated with shaking for 60 h. Rubratoxin was resolved by thin-layer chromatography. Labeled [1¹⁴C]acetate, [1,5¹⁴C]citrate, [2¹⁴C]malonate, [1¹⁴C]glucose, [U¹⁴C]glucose or [1¹⁴C]hexanoate were incorporated into rubratoxins A and B by P. rubrum 3290 and into rubratoxin B by P. rubrum 13. Incorporation of [1¹⁴C]acetate and [2¹⁴C]malonate increased when exogenous unlabeled acetate, malonate, pyruvate, or phosphoenol-pyruvate was added. Acetate incorporation was influenced by cultural conditions, attaining maximum amounts in quiescent cultures which received labeled acetate after 21 days of incubation. Acetate incorporation in shake cultures was enhanced by reduced nicotinamide adenine dinucleotide phosphate (NADPH) and by unlabeled exogenous citrate.Abbreviations GMS glucose-mineral salts - RCM replacement culture medium - TCA tricarboxylic acid - PEP phosphoenolpyruvate - RIC relative isotopic content - PI percent incorporation