The generation of the rifamycin binding site in the beta subunit of E. coli RNA polymerase through subunit interactions.

Spectral studies were performed using rifampicin quinone to investigate the generation of the rifamycin binding site in the beta subunit of E. coli RNA polymerase due to subunit interactions. The spectrum of rifampicin quinone is not significantly altered in the presence of the beta subunit. In the case of the alpha 2 beta subassembly, a negative difference spectral band at 330 nm is observed for rifampicin quinone, whereas in the presence of either the holoenzyme or core polymerase a positive band at 348 and a negative one at 318 are observed. In affinity labeling studies using 3-(2-bromo[1-14C]acetamidoethyl)-thiorifamycin, it was demonstrated that the isolated beta subunit is nonspecifically modified by this reagent. However, in the case of both the alpha 2 beta subassembly and core polymerase, the beta subunit is specifically modified.

Influence of dietary iron deficiency on hemoglobin, myoglobin, their respective reductases, and skeletal muscle mitochondrial respiration.

Male weanling rats were fed a control diet (46 ppm iron) or an iron-deficient diet (11 ppm iron) for 7 wk to determine the influence of iron deficiency on heme proteins and skeletal muscle mitochondrial respiration. At the end of 7 wk, the hemoglobin in the blood of the iron deficient rats was 35% less and skeletal muscle myoglobin was 20 to 37% less than in the control animals. The concentration of myoglobin in the heart was not appreciably diminished by iron deficiency. Cytochrome c concentration was 20% less in the heart and 35% less in the mixed-fiber gastrocnemius in the iron-deficient animals. Iron deficiency did not influence the activity of metmyoglobin reductase in either heart or skeletal muscle. There was about 30% more methemoglobin reductase activity in the red blood cells of the iron-deficient animals, which resulted in methemoglobin levels that were so low as to be virtually unmeasurable. In the iron-deficient rats, skeletal muscle mitochondrial respiration with either pyruvate-malate or palmitylcarnitine as substrate was 17 to 20% less than in the control animals. This study demonstrates that dietary iron deficiency of sufficient severity to reduce blood Hb and skeletal muscle myoglobin or cytochrome c also results in an impaired skeletal muscle oxidative capacity. The study also illustrates the preferential utilization of iron, not only between tissues, but within tissues, and tissue specific adaptive responses to iron deficiency.