Carlos Asensio

A new family of low molecular weight antibiotics from enterobacteria

Summary An apparently new family of antibiotics has been detected in the culture media of bacteria isolated from human feces. In a preliminary investigation ten different compounds have been partially purified and characterized. All of them are thermostable, soluble in methanol-water (5:1) and have a molecular weight of about 1000 or less. They show a different degree of specificity as growth inhibitors of a series of enterobacteria as well as other non-enteric microorganisms. Current work strongly suggests the existence of other similar compounds among Enterobacteriaceae and other bacterial families.

Determination of galactosamine and N-acetylgalactosamine in the presence of other hexosamines with galactose oxidase.

Abstract A specific method for the determination of galactosamine and N -acetylgalactosamine in the presence of other hexosamines is presented. The method is based on the action of galactose oxidase on these derivatives of galactose. By the use of an appropriate ion-exchange resin, an analysis of a mixture of galactose, galactosamine and N -acetylgalactosamine can also be carried out.

Identification and properties of an inducible mannokinase from Streptomyces violaceoruber

1. 1. Crude extracts from cells of several species of Streptomyces grown on different sources of carbon and energy, showed a constitutive ATP-dependent phosphorylating activity on glucose. Specifically inducible kinase activities for mannose and fructose were found in cells grown on each of these sugars. 2. 2. The activity on glucose corresponded to a typical bacterial glucokinase (ATP:d-glucose 6-phosphotransferase, EC 2.7.1.2). The activities on mannose and fructose corresponded to two enzymes of a novel pattern. 3. 3. The activity on mannose was due to a mannokinase (ATP:hexose 6-phosphotransferase, EC 2.7.1.7), which has been purified about 100-fold from extracts of Streptomyces violaceoruber. The Km of this enzyme for mannose was 0.05 mM. Glucose was also phosphorylated by this enzyme although with low affinity (Km = 4 mM). Fructose was neither a substrate nor an inhibitor. 4. 4. The inducible activity on fructose corresponded to a highly specific fructokinase (ATP:d-fructose 6-phosphotransferase, EC 2.7.1.4), which is described in the accompanying report.

Identification and properties of an inducible and highly specific fructokinase from Streptomyces violaceoruber

1. 1. An inducible fructokinase (ATP:fructose 6-phosphotransferase, EC 2.7.1.4) found in Streptomyces is described. The enzyme has been purified 400-fold from extracts of Streptomyces violaceoruber. 2. 2. This fructokinase phosphorylated fructose as the apparently unique sugar substrate, with a Km of 0.5 mM under conditions of MgATP saturation. The Km for MgATP was 0.2 mM. MgADP inhibited the enzyme competitively with MgATP (Ki, 0.2 mM). The other product, fructose 6-phosphate, did not inhibit the enzyme appreciably. 3. 3. The enzyme showed complex kinetic properties: apparent activation by free Mg2+, a sigmoid saturation curve for MgATP, and a double loop saturation curve for fructose at low MgATP concentrations.

Effect of the antibiotic microcin 140 on the ATP level and amino acid transport of Escherichia coli

Abstract Microcin 140, a novel antibiotic of low molecular weight, rapidly depletes the ATP pool of sensitive E. coli strains. This effect seems to be caused by a stimulation of the ATPase since it is not observed either in a mutant strain that lacks activity of this enzyme or in the presence of the ATPase inhibitor dicyclohexylcarbodiimide. Under these conditions the microcin does not affect the incorporation of labelled glucose into macromolecules. Microcin 140 also produces a strong inhibition of the transport of proline and phenylalanine, which is known to be coupled to the proton gradient across the bacterial membrane. There-fore, the stimulation of the bacterial ATPase can be a consequence of collapsing the proton gradient maintained by this enzyme through a proton pumping activity. These results point to a similar mechanism of action for both microcin 140 and colicin K, despite their great difference in molecular size (C.A. Plate et al., J. Biol. Chem, 249: 6138–6143, 1974) .

Fructose determination with a specific fructokinase

Abstract A method for the determination of fructose is described. It is based on the phosphorylation of this sugar by a highly specific fructokinase and the coupling of this reaction to NADP reduction by means of glucosephosphate isomerase and glucose-6-phosphate dehydrogenase. Because of the lack of interference by other sugars, the procedure is appropriate for fructose determination in biological samples where a high content of glucose interferes in other methods currently in use. Even a 100-fold excess glucose causes no detectable interference (less than 1%). The new method has been applied for the estimation of fructose in a series of normal human sera. A mean value of ca. 1 mg per 100 ml was obtained, most serums being within the range 0.5–2.

Mechanisms involved in the increased sensitivity ofEscherichia coli to microcin 15m at 42°C

Escherichia coli cells show a markedly increased sensitivity to the antibiotic microcin 15m when briefly treated at 42°C as compared to the effect at 37°C. Furthermore, mutants resistant to the microcin at 37°C become sensitive at 42°C at microcin concentrations that are inactive at 37°C. This effect can be overcome byl-methionine. The mechanism involved seems to be based on an apparent inactivation of the homoserine-O-transsuccinylase activity. As previously established, this enzyme suffers a reversible partial inactivation when the cells are shifted to 42°C and the action of the microcin at this temperature seems to bring this process to a virtually irreversible stage. In mixed cultures of the microcin-producing strain and oneE. coli strain sensitive to the antibiotic, a much stronger growth inhibition of the latter strain has been observed at 42°C than at 37°C.