Robert L. Hamill

Effects of antibiotic lonophore, A23187, on oxidative phosphorylation and calcium transport of liver mitochondria

Abstract A23187, a new antibiotic with ionophore properties, uncoupled oxidative phosphorylation in mitochondria which oxidized either malate plus glutamate or succinate. Ca 2+ , but not Mg 2+ , enhanced the uncoupling effect. Fluorescence of ANS 1 was increased by A23187 suggesting the mitochondrial membranes were de-energized. This de-energization was presumably by activation of the energy-dependent uptake of Ca 2+ . The steady-state measurements of murexide-divalent cation complexes showed that A23187 caused mitochondria to release the accumulated Ca 2+ to the medium. This reduced the transmembrane Ca 2+ gradient even though normal active Ca 2+ uptake could take place. A23187 inhibited activity of ATPase induced by 2,4-dinitrophenol, valinomycin, and Ca 2+ . The addition of Mg 2+ could prevent this inhibition presumably by maintaining the endogenous Mg 2+ concentration. The above metabolic events could be explained by the fact that molecules of A23187 function in the mitochondrial inner membrane as mobile carriers for divalent cations.

BIOCHEMISTRY AND BIOLOGICAL EFFECTS OF THE PYRAZOFURINS* (PYRAZOMYCINS): INITIAL CLINICAL TRIAL

Pyrazofurin* (PF)’*2 is one of three biologically active C-nucleosides isolated from the broth filtrates of a strain of Streptomyces candidus. Along with PF, this culture produces lesser amounts of its C1,-a-anomer, Pyrazofurin B (PFB),3*4 and a third factor, tentatively identified as OxazinomycinS (Minimycin).6 Among these and the four other naturally occurring C-nucleosides, PF alone enjoys the distinction of possessing pharmacological activity that warrants its consideration as a clinical candidate.

Biosynthesis of pyrrolnitrins by analogue-resistant mutants ofPseudomonas fluorescens

Pyrrolnitrins are a group of closely-related phenylpyrrole antibiotics synthesized from D-tryptophan by several species of Pseudomonas (Elander et al., 1968). The bacterium first shown to synthesize pyrrolnitrins in our laboratories was reported to be closely related to Pseudomonas aureofaciens (Lively et al., 1967). The strain has now been more properly classified as Pseudomonas f luorescens (Biotype E) following the system of classification proposed by Stanier et al. (1966). Biosynthetic studies have shown that D-tryptophan is a direct precursor of the antibiotic and that additions of Dtryptophan stimulate pyrrolnitrin synthesis (Lively et al., 1967; Hamill et al., 1967). However, the amounts of Dtryptophan required for maximal synthesis and the high cost of the amino acid made exploitation of this interesting discovery in large-scale production fermentors virtually impossible. With these facts in mind, a portion of our fermentation research program was directed towards isolating analogue-resistant mutants which were insensitive to feedback regulation. A number of strains resistant to 5-fluorotryptophan (5-FT) and 6-fluorotryptophan (6-FT) were induced from the wild-type pyrrolnitrin strain (Pseudomonas fluorescens A1033.8). The mutants were examined for their capacity to synthesize pyrrolnitrin in both tryptophan-supplemented and non-tryptophan-supplemented media. The results of these studies a r e described in this report.

Pyrazomycin B: Isolation and characterization of an α-C-nucleoside antibiotic related to pyrazomycin

Abstract This communication reports the isolation and structure of pyrazomycin B, the α-anomer of the anti-tumor and anti-viral antibiotic pyrazomycin. Spectral, chemical and x-ray crystallographic evidence is provided.

Effect of a new monocarboxylic acid antibiotic, A204, on the monovalent cation permeability of rat liver mitochondria

Abstract A newly isolated polyether monocarboxylic acid antibiotic, A204, is reported here to affect the translocation of monovalent cations across mitochondrial membrane. At 1 μM, A204 caused a complete inhibition of glutamate oxidation in valinomycin or monazomycin-treated rat liver mitochondria in a K + medium. The antibiotic has the following ion specificity: K + = Rb + >Na + = Cs + >Li + . Pyridine nucleotides in intact mitochondria became oxidized upon addition of A204; however, A204 did not affect respiration supported by succinate oxidation. It also causes the leakage of K + , transient release of H + , and decrease of mitochondrial volume. The monovalent cation-dependent hydrolysis of ATP in valinomycin- or monazomycin-treated mitochondria was first activated and then inhibited at concentrations of A204 above 2 μM. The inhibitory effect of A204 on adenosine triphosphatase (ATPase) is also ion dependent, but it is equally supported by Na + , K + and Rb + . We can therefore classify A204 as a new ionophore with properties shared by its predecessors, monensin, nigericin and dianemycin, which induce ion permeability in biological membranes.

Viriditoxin induces swelling and atpase by activation of calcium transport in liver mitochondria.

Abstract Viriditoxin activates ATP hydrolysis (ATPase) and swelling in rat liver mitochondria. The monocarboxylic ionophore of divalent cations, A23187, inhibits both activities at low concentrations of viriditoxin, but does not inhibit the ATPase induced by viriditoxin at concentrations above 2.5 × 10 −5 M. However, the monocarboxylic ionophore of monovalent cations, monensin, has no effect on the viriditoxin induced ATPase, but inhibits the valinomycin induced activity. Viriditoxin may facilitate the active transport of membrane bound calcium into the matrix of mitochondria

Structure of the polyether antibiotic K-41 by mass and nuclear magnetic resonance spectrometry

Using electron impact and field desorption mass spectrometry and n.m.r. spectrometry, the polyether antibiotic K-41 has been assigned structure (1).

Deacetoxycephalosporin C from Streptomyces and fungi

A new metabolite produced by two species of Streptomyces and twenty two strains of fungi, is identified as deacetoxycephalosporin C.