Reabsorption, catalyzed

Carbonic anhydrase is present in many nephron sites, but the predominant location of this enzyme is the luminal membrane of the PCT (Figure 15-2), where it catalyzes the dehydration of 2 as previously described. By blocking carbonic anhydrase, inhibitors block NaHC03 reabsorption and cause diuresis. 

Osaki, 1974 Osaki, 1966 Osaki et al., 1966). Using the kinetic values given above, they estimated that without the ferroxidase activity of Cp in the plasma 80% of the iron released from erythrocyte turnover would accumulate as non-Tf-bound Fe(ll) and thereby would be unavailable for reabsorption by the reticuloendothelial system. Furthermore, this free Fe(II) could catalyze the formation of reactive oxygen species via the Fenton reaction. This, in turn, could lead to a subsequent organismal pathophysiology (Miyajima et al., 1996 Nakano, 1993). This inference has been strikingly confirmed by research over the past 6 years in both yeasts and mammals this research has directly tested the hypothesis that multicopper oxidase-dependent ferroxidase activity is essential to eukaryotic iron homeostasis (Askwith et al., 1996 Harris et al., 1995 1998 Wessling-Resnick, 1999). 

FIGURE 28-2 NaHCO reabsorption in proximal tubule and mechanism of diuretic action of carbonic anhydrase (CA) inhibitors. A, antiporter S, symporter CH, ion channel. (The actual reaction catalyzed by carbonic anhydrase is OH + CO —> HCOg however, H2O —> OH + —> and HCO + > H2CO3, so the net reaction is H2O + CO2 —> H2CO2.)... 

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