Cefazblin was tested in vitro for its reactivity in the direct Coombs test as compared to other related antibiotics. Minimal concentrations of the antibiotics which were required to produce a direct Coombs reaction were 2.5 mg/ ml for cephalothin, 5 mg/ml for benzyl penicillin, 10 mg/ml for cephaloridine, and 40 mg/ml for cefazolin. Cefazolin even at this high concentration gave only a weak positive reaction and this depended upon the Coombs serum employed. The intensity of the positive reaction was apparently related to that of the direct antibiotic-induced lytic action on the red blood cells used (cephalothin >benzyl penicillin >cephaloridine> cefazolin). These positive reactions are believed to arise from the binding of normal globulin, directly, or otherwise indirectly through antibiotics, to the surface of red blood cell walls which have been impaired by the antibiotics. It seems therefore that these phneomena in vitro are not immunological in nature.
The mechanism of action of a new antibiotic, negamycin, was studied in Escherichia coli K12. 1. Negamycin exhibited a bacteriocidal action, and in macromolecular synthesis in negamycin-treated cells inhibition of protein synthesis was first demonstrated and then a decline of RNA synthesis followed with a little delay. The synthesis of DNA and cell wall was hardly impaired. These results indicate that protein synthesis is the primary site of inhibition by negamycin of the growing cells. 2. Negamycin inhibited in vitro protein synthesis directed by phage MS2 RNA as exogenous natural messenger RNA, and when the drug was added at the start of incubation the inhibition was marked during the first 5 or 10 minutes of the incubation and progressively decreased with the time. Furthermore, less inhibition was shown if the drug was added after protein synthesis had begun. 3. On the other hand, in vitro protein synthesis directed by endogenous natural mRNA was not inhibited but was rather stimulated by negamycin. 4. Negamycin inhibited binding of formylated methionyl-tRNA to ribosomes directed by MS2 RNA. 5. From these results negamycin seems to be a specific inhibitor of peptide chain initiation in natural mRNA directed protein synthesis and not of peptide chain elongation.
The effect of negamycin was studied on polypeptide synthesis directed by synthetic polynucleotides in Escherichia coli K12 extracts. 1. Negamycin caused misreading of genetic codes of the mRNA in the extracts: (1) Incorporation of phenylalanine normally coded for by poly U was inhibited, while that of isoleucine, serine, or leucine, not normally coded for by the polymer, was stimulated. (2) Poly A-directed lysine or glutamic acid incorporation and poly C-directed proline or leucine incorporation were both stimulated by the drug. 2. Binding of phenylalanyl-tRNA to ribosomes-poly U complex was weakly inhibited by negamycin. On the other hand, that of isoleucyl-tRNA to the complex was about threefold stimulated by the drug. 3. Puromycin reaction, an analogue of peptide bond forming reaction, with N-acetyl-phenylalanyl-tRNA was not affected by negamycin. 4. In rat liver extracts, the incorporation of phenylalanine directed by poly U was much less affected by negamycin.
Streptomyces sp., strain No. T-7545 was found to produce new antibiotics, validamycins A and B that are effective for the control of sheath blight of rice plants. The validamycins exhibit no in vitro activity. A taxonomic study of strain No. T-7545 was carried out and it was characterized as follows: It forms gray to gray and yellow aerial mycelium, bright yellow to yellow ocher vegetative mycelium and faint, brownish yellow diffusible pigment, good growth and development of abundant aerial mycelium with the formation of coiled chains of spores at 25-45°C, and black moist areas in the aerial mycelium on certain media. As a result of comparison of strain No. T-7545 with known species, the name Streptomyces hygroscopicus WAKSMAN et HENRICI, 1948 var. limoneus nov. var. is proposed.
Macrolide antibiotics of the polyene antifimgal subgroup undergo aerial autoxidation in methanol solution by a radical addition process which can be inhibited by antioxidants. The related pentaenes of the filipin complex, which has the main component (I), and lagosin (II) yield as the major primary products the corresponding tetraene epoxides (III) and (IV), which are probably mixtures of diastereoisomers. The structures of the products were established by spectroscopy and chemical degradation. Extended autoxidation leads to higher oxidation products and ultimately to polymeric materials.
Anticapsin is a new biologically active metabolite isolated from the culture filtrate of a strain of Streptomyces griseoplanus. The metabolite inhibits the formation of the hyaluronic acid capsules of Streptococcus pyogenes at a minimal concentration of 3 mcg/ml. Anticapsin (C9H13O4N), an amino acid (pKa=4.3; 10.1 in 66% DMF), is chemically related to bacilysin.