Structure and mechanism of copper, zinc superoxide dismutase

Copper, zinc superoxide dismutase (SOD) catalyses the very rapid two-step dismutation of the toxic superoxide radical (O-2) to molecular oxygen and hydrogen peroxide through the alternate reduction and oxidation of the active-site copper. We report here that after refitting and further refinement of the previous 2 A structure of SOD2, analysis of the new model and its calculated molecular surface shows an extensive surface topography of sequence-conserved residues stabilized by underlying tight packing and H-bonding. There is a single, highly complementary position for O-2 to bind to both the Cu(II) and activity-important Arg 141 with correct geometry; two water molecules form a ghost of the superoxide in this position. The geometry and molecular surface of the active site, together with biochemical data, suggest a specific model for the enzyme mechanism.     

A technique for improving salivary chromosome preparations

Zusammenfassung Es wird eine verbesserte Methode zur Herstellung von Quetschpräparaten von Speicheldrüsenchromosomen beschrieben. Die Methode gibt scharfe Bilder der feinsten Chromosomenbänder auf klarem Hintergrund.

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Research supported by U.S. Public Health Service Research Grants No. GM-11609 and GM-19616 from the National Institute of General Medical Sciences.     

The effect of pyridoxine and pyridoxal on the circulatory response of rats to microwave irradiation

Résumé L'administration intraveineuse de pyridoxine et pyridoxal (10 mg/kg) à des rats anesthésiés inhibe l'augmentation du rendement du cocur. En même temps, une hyperthermie est provoquée par l'irradiation du corps entier avec des ondes de longueur minime (2,450 Mc. c.w. 0.08/w/cm²). Cet effet peut être attribué à l'interaction de ces composés d'amines vasoactifs libérés pendant l'irradiation.     

Disposition of intra-articularly injected hydrocortisone acetate,hydrocortisone free alcohol and cortisone acetate in arthritis

Riassunto In pazienti affetti da artrite reumatoide viene iniettato cortisone acetato, idrocortisone acetato, o idrocortisone, nel cavo sinoviale artritico.La durata del riassorbimento di questi 17-idrossicorticoidi; la loro distribuzione nelle cellule e nel fluido articolare e nelle cellule del rivestimento sinoviale; le andamento del processo idrolitico dei composti acetati, studiati con mezzi chimici e cromatografici, si prestano a commenti utili ad interpretare la maggiore efficacia locale dell'idrocortisone.

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Supported by a grant from the Helen Augusta Parkhill Foundation.—Communication at the 8^th International Congress of Rheumatic Diseases, Geneva, August 1953.     

Frequent chromosomal translocations induced by DNA double-strand breaks

The faithful repair of DNA damage such as chromosomal double-strand breaks (DSBs) is crucial for genomic integrity. Aberrant repair of these lesions can result in chromosomal rearrangements, including translocations, which are associated with numerous tumours. Models predict that some translocations arise from DSB-induced recombination in differentiating lymphoid cell types or from aberrant repair of DNA damage induced by irradiation or other agents; however, a genetic system to study the aetiology of these events has been lacking. Here we use a mouse embryonic stem cell system to examine the role of DNA damage on the formation of translocations. We find that two DSBs, each on different chromosomes, are sufficient to promote frequent reciprocal translocations. The results are in striking contrast with interchromosomal repair of a single DSB in an analogous system in which translocations are not recovered. Thus, while interchromosomal DNA repair does not result in genome instability per se, the presence of two DSBs in a single cell can alter the spectrum of repair products that are recovered.