R. Morenosanchez et al., MODULATION OF 2-OXOGLUTARATE DEHYDROGENASE AND OXIDATIVE-PHOSPHORYLATION BY CA2-CORTEX MITOCHONDRIA( IN PANCREAS AND ADRENAL), Archives of biochemistry and biophysics, 319(2), 1995, pp. 432-444
The effect of external free Ca2+ ([Ca2+]ex) on the 2-oxoglutarate dehy
drogenase (2-OGDH) activity and the rate of state 3 respiration was st
udied in dog pancreas and adrenal cortex mitochondria. A method for th
e preparation of mitochondria from pancreas, free of zymogen granules,
was developed. The mitochondria showed high respiratory control value
s and maintained adequate ADP/O ratios in the course of several hours.
Half-maximal stimulation (K-0.5) of 2-OGDH activity and state 3 respi
ration by Ca2+ was decreased twofold by spermine, in both pancreas and
adrenal cortex mitochondria incubated with Mg2+; Na+ increased the K-
0.5 value for Ca2+ in both kinds of mitochondria. The matrix Ca2+ cont
ent was enhanced by spermine at different [Ca2+]ex. The Ca2+ gradient
([Ca2+]m/[Ca2+]ex) determined in Fluo 3-loaded pancreas mitochondria w
as found to be below 1, either in the presence of Nai or in the absenc
e of spermine. The protonmotive force was increased by 1 mu M Ca2+, in
state 3 conditions, by 6-8 mV; lower Ca2+ concentrations kept the Hgradient rather constant. An increase in the spermine/Mg2+ ratio at co
nstant external Ca2+ resulted in stimulation of the 2-OGDH activity an
d state 3 respiration. The data indicate that matrix Ca2+ may regulate
the rate of ATP synthesis in pancreas and adrenal cortex mitochondria
, through the modulation of 2-OGDH and the maintenance of a high Hf gr
adient. In addition to changes in external Ca2+, the variation in the
spermine/Mg2+ ratio may also exert control of oxidative phosphorylatio
n. (C) 1995 Academic Press, Inc.