Role of the naphthoquinone moiety in the biological activities of sakyomicin A.

Abstract

The naphthoquinone moiety was proven to be essential to the biological activities of sakyomicin A using various naphthoquinone derivatives. Among the naphthoquinones tested, juglone (5-hydroxy-1,4-naphthoquinone) which resembles the partial structure of sakyomicin A was the most active in cytotoxicity against murine lymphosarcoma L5178Y cells, electron acceptor function in the oxidation of NADH by Clostridium kluyveri diaphorase or rat liver mitochondria and inhibition against avian myeloblastosis virus reverse transcriptase.The significantly lower cytotoxicity of sakyomicin A as compared with juglone was attributable to its poor membrane transport.The inhibition of reverse transcriptase activity may result from the interaction between a sulfhydryl group in the active center of the enzyme and quinone groups of the naphthoquinones and sakyomicin A.Retroviruses contain an enzyme called reverse transcriptase, which is responsible for the first step of the integration of viral genomes into cellular DNA, and agents which inhibit this enzyme are therefore of potential therapeutic use against viral infection.In the course of our screening for the enzyme inhibitors against reverse transcriptase of avian myeloblastosis virus (AMV), novel substances, retrostatinl) and chromostin2), and limocrocin3) which had been reported as a pigment produced by Streptomyces limosus') were isolated as the specific enzyme inhibitors. Furthermore, one of the active metabolites of Streptomyces origin was proven to be identical with sakyomicin A5), an antibiotic produced by a strain of Nocardiae6). Besides an inhibitory activity against reverse transcriptase5), sakyomicin A showed an electron acceptor activity in the oxidation of NADH by bacterial diaphorase or mitochondria7). Similar to streptonigrin which is another potent inhibitor of reverse transcriptasee•8,9), only a catalytic amount of sakyomicin A was necessary for the oxidation of NADH, though exogenous NADH was oxidized by mitochondria in the presence of sakyomicin A but not streptonigrin.In accordance with the oxidation of NADH, sakyomicin A was reduced to a hydroquinone which, in turn, autoxidized to a quinone accompanying the generation of hydrogen peroxide. In contrast to streptonigrin which had been reported to primarily interfere with oxidative phosphorylation in mitochondria by facilitating the oxidation of NADH by DT-diaphorasell-12), the enzyme involved in sakyomicin A-dependent oxidation of NADH appeared to be in a different compartment in mitochondria from DT-diaphorase.The present study was undertaken to examine the role of the naphthoquinone moiety in the biological activities of sakyomicin A using various naphthoquinone derivatives.

Respiratory stimulation and generation of superoxide radicals in Pseudomonas aeruginosa by fungal naphthoquinones

“…The stimulation of oxygen consumption and the induction of oxidase activity in the presence of electron transport inhibitors are caused by electron acceptors (Hayashi et al 1982;Inoue et al 1986). The characteristics of electron acceptors can be clarified when the effects of these compounds on diaphorase activity are examined Take et al 1986). These naphthoquinones acted as electron acceptors in bacterial diaphorase.…”

“…The reaction was carried out in a solution composed of 9.0 units of diaphorase (from Clostridium kluyveri; Oriental Yeast, Tokyo, Japan), 0.9 mM NADH, 0.05 mM EDTA, and 10 mM Tris-HCl (pH 8.0) in a total volume of 1 ml (Take et al 1986). The mixture was incubated at 37°for 5 min.…”