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Protein-O-methyltransferase in brain synaptosomal fraction under normal, ischemic and hypoxic conditions. Possible
Abstract:
Activity of protein-O-methyltransferase in synaptosomal fractions was obtained. Km values calculated for S-adenosylmethionine as substrate were 1 microM and Vmax = 4.3 pmoles/mg p/min. In the presence of gelatin (exogenous protein acceptor), activity was about 3 times higher. Without gelatin, activity of endogenous protein-O-methyltransferase decreased by about 20% under hypoxic conditions and by about 15% in ischemia. Exogenous activity under both hypoxic and ischemic conditions did not change. These results can possibly be explained by the changes in methyl acceptor proteins. In normal conditions, after inhibition methylcarboxylation by S-adenosyl-L-homocysteine, the decrease of GABA uptake and increase in the uptake of dopamine were observed. Uptake of serotonine and noradrenaline were unchanged.
Insights
Protein-O-methyltransferase activity in brain synaptosomes decreases under hypoxia and ischemia. Changes in methyl acceptor proteins may explain altered neurotransmitter uptake, affecting GABA and dopamine levels.
Area of Science:
- Neurochemistry
- Enzymology
- Cellular Neuroscience
Background:
- Protein-O-methyltransferase (POMT) plays a role in post-translational modifications.
- Synaptosomes are crucial for studying neurotransmitter transport and neuronal function.
Purpose of the Study:
- To investigate the activity of POMT in synaptosomal fractions under normal, hypoxic, and ischemic conditions.
- To explore the impact of POMT activity on neurotransmitter uptake.
Main Methods:
- Enzyme kinetics were used to determine Km and Vmax for S-adenosylmethionine.
- Synaptosomal fractions were subjected to hypoxic and ischemic conditions.
- Neurotransmitter uptake assays (GABA, dopamine, serotonin, noradrenaline) were performed.
Main Results:
- POMT activity showed a Km of 1 µM for S-adenosylmethionine and Vmax of 4.3 pmoles/mg protein/min.
- Activity was significantly higher with an exogenous protein acceptor (gelatin).
- Endogenous POMT activity decreased by ~20% in hypoxia and ~15% in ischemia, while exogenous activity remained unchanged.
- Inhibition of methylcarboxylation led to decreased GABA uptake and increased dopamine uptake.
Conclusions:
- Hypoxia and ischemia reduce endogenous POMT activity in synaptosomes.
- Altered methyl acceptor proteins likely contribute to changes in neurotransmitter uptake under these conditions.
- POMT activity modulation may impact neuronal signaling pathways.
