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Biomedical subjects

S M Block

Publications and source records attributed to S M Block.

75 records · Page 5Linked to original sources

Successive incorporation of force-generating units in the bacterial rotary motor.

Mot mutants of Escherichia coli are paralysed: their flagella appear to be intact but do not rotate. The motA and motB gene products are found in the cytoplasmic membrane; they do not co-purify with flagellar basal bodies isolated in neutral detergents. Silverman et al. found that mot mutants could be ' resurrected ' through protein synthesis directed by lambda transducing phages carrying the wild-type genes. Here, we have studied this activation at the level of a single flagellar motor. Cells of a motB strain carrying plasmids in which transcription of the wild-type motB gene was controlled by the lac promoter were tethered to a glass surface by a single flagellum. These cells began to spin within several minutes after the addition of a lac inducer, and their rotational speed changed in a series of equally spaced steps. As many as 7 steps were seen in individual cells and, from the final speeds attained, as many as 16 steps could be inferred. These experiments show that each flagellar motor contains several independent force-generating units comprised, at least in part, of motB protein.

Cell Movement↗

Neutrophil storage pool depletion in septic, neutropenic neonates.

A prospective study was done to determine the incidence of neutrophil storage pool (NSP) depletion in clinically septic neonates with peripheral neutropenia (less than 1500/mm3). Infants with NSP depletion were then randomized in a controlled study of polymorphonuclear leukocyte transfusions. Bone marrow examinations were done in 13 patients, and NSP depletion was noted in 3 (23%) patients. All patients with no NSP depletion had peripheral neutrophil recovery and 8 of 10 survived. Complications of meningitis contributed to both deaths. Two of the three patients with NSP depletion died. Neither the initial severity of illness nor the degree of peripheral neutropenia were predictive either of NSP depletion or of mortality. Most neonates with severe peripheral neutropenia and clinical sepsis had peripheral neutrophil recovery and survived with conservative management. Those at high risk could be identified only by examination of the NSP. Only those patients with NSP depletion should be considered for controlled studies of polymorphonuclear leukocyte transfusions.

Agranulocytosis↗