Binding of β-lactam antibiotics to the exocellular dd-carboxypeptidase–transpeptidase of Streptomyces R39

Benzylpenicillin and cephaloridine reacted with the exocellular dd-carboxypeptidase–transpeptidase from Streptomyces R39 to form equimolar and inactive antibiotic–enzyme complexes. At saturation, the molar ratio of chromogenic cephalosporin 87-312 to enzyme was 1.3:1, but this discrepancy might be due to a lack of accuracy in the measurement of the antibiotic. Spectrophotometric studies showed that binding of cephaloridine and cephalosporin 87-312 to the enzyme caused opening of their β-lactam rings. Benzylpenicillin and cephalosporin 87-312 competed for the same site on the free enzyme, suggesting that binding of benzylpenicillin also resulted in the opening of its β-lactam ring. In Tris–NaCl–MgCl₂ buffer at pH7.7 and 37°C, the rate constants for the dissociation of the antibiotic–enzyme complexes were 2.8×10⁻⁶, 1.5×10⁻⁶ and 0.63×10⁻⁶s⁻¹ (half-lives 70, 130 and 300h) for benzylpenicillin, cephalosporin 87-312 and cephaloridine respectively. During the process, the protein underwent reactivation. The enzyme that was regenerated from its complex with benzylpenicillin was as sensitive to fresh benzylpenicillin as the native enzyme. With [¹⁴C]benzylpenicillin, the released radioactive compound was neither benzylpenicillin nor benzylpenicilloic acid. The Streptomyces R39 enzyme thus behaved as a β-lactam-antibiotic-destroying enzyme but did not function as a β-lactamase. Incubation at 37°C in 0.01m-phosphate buffer, pH7.0, and in the same buffer supplemented with sodium dodecyl sulphate caused a more rapid reversion of the [¹⁴C]benzylpenicillin–enzyme complex. The rate constants were 1.6×10⁻⁵s⁻¹ and 0.8×10⁻⁴s⁻¹ respectively. Under these conditions, however, there was no concomitant reactivation of the enzyme and the released radioactive compound(s) appeared not to be the same as before. The Streptomyces R39 enzyme and the exocellular dd-carboxypeptidase–transpeptidase from Streptomyces R61 appeared to differ from each other with regard to the topography of their penicillin-binding site.     

Kinetics of denaturation of DNA

The kinetics of denaturation of DNA have been studied by relaxation techniques. Examination of the terminal relaxation times for a variety of DNA's under a variety of conditions has shown that DNA denaturation is principally a hydrodynamically limited process. Measurements within the helix–coil transition have demonstrated that the experimentally measured terminal relaxation times are a function of the following: (1) position in the helix–coil transition; (2) ionic strength of the solvent; (3) solvent viscosity; (4) DNA concentration; (5) molecular weight; (6) number and position of single-strand breaks. The dependence of the terminal relaxation time on the above mentioned factors can be attributed to hydrodynamic effects. Thus a hydrodynamic model for DNA unwinding is required. The model which best fits the data involves the assumption of a rotational frictional coefficient independent of molecular weight. This assumption is suggested by the fact that the relaxation time is proportional to the first power of the molecular weight.     

Girls' Puberty Rites and Matrilocal Residence

This paper challenges the view of Judith K. Brown (1961) and Peter Kloos (1969) that matrilocal residence tends to cause girls' puberty rites. It shows how improbable this hypothesis is for western North America, where data are plentiful, and suggests that it is unlikely for the rest of the world. Girls' puberty rites seem to be earlier in most localities because of much greater world frequency and dominance among hunters, gatherers, and fishers, while matrilocal residence appears mainly to have stemmed from female hand farming at a later date. [causality, evolution, puberty rites—female, matrilocal residence, migration as agent of culture spread]     

B12 Coenzyme-dependent Ribonucleotide Reductase in Rhizobium Species and the Effects of Cobalt Deficiency on the Activity of the Enzyme

This investigation revealed that the ribonucleotide reductases in extracts of Rhizobium leguminosarum, R. trifolii, R. phaseoli, R. japonicum, and R. meliloti 3DOal (ineffective in nitrogen fixation) are dependent upon B(12) coenzyme for activity. Rhizobium and certain Lactobacillus species are the only two groups of organisms known to contain B(12) coenzyme-dependent ribonucleotide reductases. Extracts of cobalt-deficient R. meliloti cells assayed in the presence of optimum B(12) coenzyme showed a 5- to 10-fold greater ribonucleotide reductase activity than comparable extracts from cells grown on a complete medium. Furthermore, cobalt-deficient cells were abnormally elongated and contained reduced contents of deoxyribonucleic acid. The addition of purified deoxyribonucleosides to cobalt-deficient cultures of R. meliloti failed to alleviate deficiency symptoms.     

Properties of the inactive ribosomal components in rat liver and hepatoma

1. The relative concentrations of the inactive ribosomal components were compared in normal and regenerating rat liver and in two transplantable rat hepatomas (hepatomas 7800 and 5123D). 2. The size of the ribosomal-subunit pools in normal liver was not significantly affected by partial hepatectomy or neoplasia although, as shown previously, significant changes do occur in the monomer pool. 3. Further, the subunit pools in both liver and hepatoma were not significantly influenced by several treatments that caused dramatic changes in the size of the ribosomal monomer (and dimer) pools. 4. The high concentration of inactive monomers and dimers in the hepatomas appears to arise from limitations at the translational level, since they can be incorporated into pre-existing polyribosomes under the influence of cycloheximide.     

Hyperthyroidism with Periodic Paralysis

Hyperthyroidism may be associated with hypokalemic periodic paralysis. Two cases are presented demonstrating intermittent attacks of flaccid paralysis associated with clinical symptoms, signs and laboratory findings of hyperthyroidism. During an attack, one patient had a serum potassium of 2.1 mEq. per litre.Various factors such as trauma, exposure to cold, excessive carbohydrate ingestion and certain medications have been stated to precipitate an episode of paralysis. Attacks may range from mild weakness to generalized flaccid paralysis with loss of deep tendon reflexes. Several reported patients have died owing to cardiac arrest or respiratory paralysis.During attacks, the serum potassium is usually in the range of 2.2 to 3.2 mEq. per litre. It is postulated that a metabolic abnormality affecting the muscle-cell membrane can occur in the hyperthyroid state resulting in a shift of potassium to the intracellular position, thus producing a situation of hyperpolarization of the muscle-cell membrane which in turn alters the muscle contractibility.The importance of recognizing the unusual association of hypokalemic periodic paralysis with hyperthyroidism is stressed because, with successful treatment of the hyperthyroidism, the episodes of paralysis disappear.     

Therapy of Staphylococcal Infections in Monkeys. IV. Further Comparison of Triacetyloleandomycin and Erythromycins

Intravenous inoculation of a penicillin-resistant, phage type 80/81 staphylococcus caused lethal infection in 8 of 15 untreated monkeys. Daily intragastric administration of 50 mg/kg of triacetyloleandomycin, erythromycin estolate, and erythromycin ethylsuccinate was followed by mortalities of 0 of 16, 3 of 16, and 3 of 10, respectively. At dose levels of 25 and 12.5 mg/kg, none of 7 and 4 of 7 receiving triacetyloleandomycin and erythromycin estolate, respectively, died, as compared to 3 of 4 deaths in controls. In vitro sensitivity data and serum antibacterial levels would suggest that triacetyloleandomycin would be the least effective therapeutically. However, this prediction was not fulfilled in these studies of experimental infections in monkeys wherein triacetyloleandomycin was a very effective antimicrobial agent.