Studies on the functional significance of mitochondrial bound hexokinase in rabbit reticulocytes.
Mitochondria from rabbit reticulocytes contain about 50% of the total reticulocyte hexokinases. The proportion of mitochondrial hexokinases may be changed under different metabolic conditions. Mitochondrial bound and soluble hexokinases exhibit different kinetic properties (KMATP and glucose-6-phosphate inhibition). The respiratory rate of isolated reticulocyte mitochondria in the presence of glucose depends on the glucose-6-phosphate concentration, as the ADP generation by the endogenous hexokinases is strongly inhibited by glucose-6-phosphate. In the experimental system all intermediary states of mitochondrial respiration can be adjusted between the state of maximal activity (state 3 or active state) and the controlled or resting state (state 4) by different glucose-6-phosphate levels. The stationary levels of the extramitochondrial adenine nucleotides in this experimental system have been measured. The rate of mitochondrial respiration and ATP formation depends on the extramitochondrial ATP/ADP ratio. At ratios of about 10 and lower the mitochondria are in their maximum phosphorylation state, at higher ratios the mitochondrial ATP formation is controlled by the extramitochondrial ATP/ADP ratio. It is postulated that the close intercounnection between the mitochondrial hexokinase and the mitochondrial ATP forming system in reticulocytes is of funcitonal significance for mitochondrial-cytosolic interactions in rabbit reticulocytes and probably in other types of cells with mitochondrial hexokinases, too.
D000244:Adenosine Diphosphate / Q000097:blood; D000255:Adenosine Triphosphate / Q000097:blood; D000818:Animals; D001665:Binding Sites; D003600:Cytosol / Q000378:metabolism; D005958:Glucosephosphates / Q000097:blood; D006593:Hexokinase / Q000097:blood*; D066298:In Vitro Techniques; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D010101:Oxygen Consumption; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology* / Q000378:metabolism
D005958:Glucosephosphates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D006593:Hexokinase