Abstract: | Abstract— A 20–30 per cent stimulation of ATPase activity by added NaHCO3 was found in homogenates of a variety of mammalian tissues. The subcellular distribution of this (HCO3-)—stimulated activity was examined in detail using rat cerebral cortex. The stimulation was specific for the HCO3- ion and was predominantly localized in the mitochondrial subcellular fraction, in which a 2-fold stimulation by HCO3- was found. The effect of inhibitors supported the identification as the mitochondrial ATPase. Both sodium azide and thiocyanate were inhibitory. The effects of varying the Mg2+ concentration, HCO3- concentration, and pH were also studied. In the presence of HCO3- the Km for ATP was reduced approximately 3-fold. There was no effect of HCO3- on the ma + K) ATPase or Mg2+ ATPase from the microsomal fraction of rat cerebral cortex. Our findings have been discussed in relation to previous work on HCO3- stimulation of ATPae activity in subcellular fractions from other tissues, as well as its possible relevance to the known effects of HCO3- and carbonic anhydrase on active ion transport. |