Function of phospholipids in Escherichia coli. Characterization of a mutant deficient in cardiolipin synthesis.

Screening of a collection of temperature-sensitive mutants of Escherichia coli for defects in phospholipid metabolism led to the isolation of a mutant deficient in cardiolipin synthesis. The defective gene, named cls, is closely linked to the trp marker and maps at about Minute 27 on the E. coli chromosome. After transfer of cls to a defined genetic background by transduction, the mutant has the following properties as compared to an isogenic wild type. Exponentially growing cells show a reduction in cardiolipin content by a factor of at least 15 (less than 0.2 mol % of the total phospholipids). A crude membrane fraction derived from the mutant is unable to synthesize cardiolipin from phosphatidylglycerol in vitro. The mutant has no distinctive phenotype regarding its growth properties, membrane-associated respiratory functions, or the ability to insert bacteriophage M13 coat protein into the cell envelope. The cls mutation confers a 5-times reduction in the turnover of the phosphate moiety of phosphatidylglycerol.     

Neonatal respiratory distress: potential for prevention.

A prospective study was conducted of 100 consecutive admissions to the neonatal intensive care unit of the Hospital for Sick Children, Toronto, of infants with respiratory distress syndrome or transient tachypnea of the newborn. It was found that in 15% of cases the illness was completely preventable, being the result of unintentionally premature termination of pregnancy. Significant intrapartum asphyxia occurred in 44% of the infants in whom respiratory distress syndrome developed. Factors placing the pregnancy at high risk were present antenatally in most cases, and most of the deliveries took place in hospitals without adequate facilities or staff, or both, for the requirements of the infant at and following birth.     

An extended kinetic analysis of valinomycin-induced Rb-transport through monoglyceride membranes.

The time course of the current following a voltage jump, which is applied to monoglyceride bilayers in the presence of valinomycin, shows two relaxation times. This is basically in agreement with a simple carrier model which has been described in full detail formerly. Relaxation times and amplitudes allow a calculation of the rate constants of the transport model. The presented data supplement an analysis which was hitherto based only on the slower relaxation process and on information derived from the nonlinearity of current-voltage characteristics. The additional resolution of the faster relaxation time allowed an approximate determination of the voltage dependence of the translocation rate constant for carrier-ion-complex and provided evidence for a small voltage dependence of the interfacial reaction. The dependence of the relaxation parameters on the ion concentration in the aqueous phase was interpreted assuming a saturation of the ion concentration at the reaction plane at high bulk concentrations.