Iron (Fe) is a transition metal whose physicochemical properties make it the focus of vital biological processes in virtually all living organisms. Paradoxically, the same characteristics that biochemistry exploits make Fe a potentially lethal substance. Differentiating erythroid cells acquire vast amounts of Fe at a breakneck rate. After cells acquire Fe via receptor‐mediated endocytosis, it is transferred from the endosome to the mitochondrial matrix where ferrochelatase catalyzes the insertion of the metal into protoporphyrin IX to form heme. Using both biochemical and microscopic strategies, we show that developing erythroid cells deliver the metal directly from endosome to mitochondrion, bypassing the cytosol. Reticulocytes whose cytosol was loaded with a membrane‐impermeant Fe chelator elicited no decrease in Fe incorporation into heme when Fe was delivered to the cells by the physiological chelate, transferrin (Tf). Additionally live‐cell imaging revealed a movement of Tf‐containing structures to mitochondria which was associated with an increase in mitochondrial iron. Using electron microscopy we observed an interorganellar association of a tubular, Tf‐containing network with mitochondria.
A study of the rate of heat transfer to air at low velocities was performed in a heated stainless tube, 4.42‐in. inside diameter and 102‐in. long. The air flowed upward through the tube, under which conditions the buoyancy forces aided the forced flow. The investigation covered a Reynolds number range from 385 to 4,930, and nominal wall temperatures of 100, 500 and 950°C. For laminar aiding flow, the local Nusselt number could be correlated with (NGr/NRc). For turbulent flow, the local Nusselt number was correlated with the Grashof number independently of the axial position for fully‐developed flow, and agreed with published data for pure free convection.
The rate of heat transfer to air flowing downward at low velocities through a heated tube was studied. The apparatus has been described in a previous work. The investigation covered a flow rate ranging from 85 to 930 lb./hr.ft.2, (NRc) from 380 to 6,900, (NGr) from 0.18 × 106 to 7.3 × 106 and nominal wall temperatures of 100, 500 and 950°C.The local Nusselt number could be correlated with the Grashof number independently of its axial position, over a range of Grashof numbers not previously investigated. In particular, it was noted that a marked change in the slope of the (NNu)‐vs‐(NGr) curve occurred around a Grashof number of 106.
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