Pyruvate dehydrogenase complex (PDC) from rat kidney or pig heart previously inactivated by phosphorylation (PDHP) was activated in vitro by PDHP
phosphatase from kidneys of starved or fed rats.
Starvation for 48 h of the rats from which the PDC was prepared led to a decrease in the rate of activation of PDC at early time periods (< 2 min), particularly at submaximal concentrations of Mg2+. Using intact permeable kidney mitochondria incubated for 15 sec, it was found that
starvation of rats more than doubled the Mg2+ concentration at which the half maximal increment of PDC activity (PDCa) was observed. Reduction of PDHP
phosphatase activity due to
starvation was also apparent when
phosphatase was separated from PDC and recombined with PDC from the same or different animals.
Intraperitoneal injection of
insulin and
glucose 1 h before sacrifice of starved rats prevented the reduction of PDHP
phosphatase activity whether or not
protein synthesis was inhibited. The effect of
insulin in restoration of PDHP
phosphatase activity of starved rats was not mimicked by 5-methylpyrazole 3-carboxylic
acid, an inhibitor of lipolysis. When renal PDHP
phosphatase was incubated with pig heart PDC in the presence of 10 mM Mg2+ and 0.1 mM Ca2+ the increment in PDCa, in 1 min was 30% of fully activated PDC activity (PDCt) observed after 15 min. Removal of
divalent cations did not affect the increment in 1 min but prevented further increments. Conversely
okadaic acid diminished 1 min increment but did not disturb PDCt. It is suggested that the different behaviour of renal PDC from fed and starved animals may partly be due to different divalent
cation independent PDHP
phosphatase activity.