RESUMO
Ferrochelatase in membrane preparations from Azospirillum brasilense displayed an activity of 2.17 mumol protoheme formed.h-1.mg protein-1 which is 10-fold greater than previous reports for other bacteria. This ferrochelatase showed an apparent Km of 20.9 microM for Fe2+, a pH optimum of 6.0-6.5, and stimulation by oleic or stearic acids. Co2+, Cu2+ and Zn2+ inhibited the incorporation of Fe2+ into protoporphyrin IX while Ni2+ and Mg2+ had no effect on protoheme synthesis. Activity with Fe2+ and mesoporphyrin IX was less than with protoporphyrin IX but deuteroporphyrin IX produced the highest rate of protoheme synthesis. The membrane fraction containing ferrochelatase activity was found to insert Cu2+, Ni2+, Zn2+ and Co2+ enzymatically into protoporphyrin IX to produce metalloporphyrins. Cu2+ incorporation into protoporphyrin IX proceeded at a rate greater than with Fe2+ and the Km for Cu2+ was 21.9 microM.
Assuntos
Azospirillum brasilense/enzimologia , Ferroquelatase/metabolismo , Metais/metabolismo , Cátions Bivalentes/metabolismo , Ácidos Graxos/metabolismo , Heme/biossíntese , Especificidade por SubstratoRESUMO
The cell surface of Azospirillum brasilense was probed by using fluorescein isothiocyanate (FITC)-labeled lectins, with binding determined by fluorescence-activated flow cytometry. Cells from nitrogen-fixing or ammonium-assimilating cultures reacted similarly to FITC-labeled lectins, with lectin binding in the following order: Griffonia simplicifolia II agglutinin > Griffonia simplicifolia I agglutinin > Triticum vulgaris agglutinin > Glycine max agglutinin > Canavalia ensiformis agglutinin > Limax flavus agglutinin > Lotus tetragonolobus agglutinin. The fluorescence intensity of cells labeled with FITC-labeled G. simplicifolia I, C. ensiformis, T. vulgaris, and G. max agglutinins was influenced by lectin concentration. Flow cytometry measurements of lectin binding to cells was consistent with measurements of agglutination resulting from lectin-cell interaction. Capsules surrounding nitrogen-fixing and ammonium-assimilating cells were readily demonstrated by light and transmission electron microscopies.
RESUMO
This report provides evidence of nosocomial transmission of Haemophilus influenzae type b infection between two children in an acute care hospital. In the past, transmission of infection between these children would have gone unrecognized, because the isolates from the respective cases differed in susceptibility to ampicillin. However, the outer membrane protein profile of the two isolates was identical and has previously been observed in less than 2% of type b Haemophilus isolates from patients with invasive disease in the St. Louis area. Thus the likelihood is very low that these two children were both infected with this strain by chance alone (P less than 0.0004). From previous experience, the risk of transmission of Haemophilus in an acute care setting would appear to be very low. However, nosocomial transmission may occasionally occur.