Group-selective reagent modification of the sodium- and chloride-coupled glycine transporter under native and reconstituted conditions.

Glycine transporter from rat brain stem and spinal cord is inactivated by specific sulfhydryl reagents. Modification of lysine residues also promotes a decrease of the transporter activity but in a lesser extent than that promoted by thiol group reagents. Mercurials showed a more marked inhibitory effect than maleimide derivatives. SH groups display a similar reactivity for p-chloromercuribenzenesulfonate (pCMBS) and mersalyl in synaptosomal membrane vesicles and proteoliposomes reconstituted with the solubilized transporter. However, different reactivity is observed with N-ethylmaleimide (MalNEt), the greatest effect being attained in membrane vesicles. The rate of inactivation by pCMBS and MalNEt is pseudo-first-order showing time- and concentration-dependence. pCMBS and MalNEt decrease the Vmax for glycine transport and to a lesser extent act on the apparent Km. Treatment with dithiothreitol (DTT) of the transporter modified by pCMBS results in a complete restoration of transporter activity indicating that the effect exercised by the reagent is specific for cysteine residues on the protein. It is concluded that SH groups are involved in the glycine transporter function and that these critical residues are mostly located in a relatively hydrophilic environment of the protein.     

Homologous recombination in prokaryotes: enzymes and controlling sites

A common step in prokaryotic recombination appears to be the synapsis of the 3'-end of single-stranded DNA with duplex DNA to form a D-loop. The enzymatic mechanisms by which 3'-ends are produced and by which D-loops are converted into recombinant molecules are illustrated by proposed mechanisms of recombination by the Escherichia coli RecBCD pathway and the phage lambda Red pathway. The enzymes promoting recombination and the special DNA sites at which they act are emphasized. Recombination by other E. coli pathways and in other prokaryotes is compared with these mechanisms.     

Hip fractures in healthy patients: operative delay versus prognosis.

One hundred and forty five women who had undergone hemiarthroplasty for a subcapital fracture of the femoral neck but who were otherwise fit were studied to determine whether undue delay between injury and operation influenced their social circumstances three months after surgery. The median delay for those patients who showed good rehabilitation at three months was 29 hours, but for those who showed poor rehabilitation it was 57 hours. This difference was significant. It is suggested that a subcapital fracture in an otherwise fit elderly patient should therefore be regarded as a surgical emergency.     

Determination of the A-T content of DNA by second-derivative ultraviolet spectroscopy

A method for the determination of the A-T content of DNA based on second-derivative ultraviolet spectra is presented. It allows measurement in a wide range of pH values, ionic strengths, and buffer media. It is nondestructive for the sample and requires not more than 10 micrograms of DNA.