Regulatory effects of 5'-deoxypyridoxal on glutamate dehydrogenase activity and insulin secretion in pancreatic islets.
It has been known that glutamate, generated by glutamate dehydrogenase (GDH), acts as an intracellular messenger in insulin exocytosis in pancreatic beta cells. Here we demonstrate the correlation of GDH activity and insulin release in rat pancreatic islets perfused with 5'-deoxypyridoxal. Perfusion of islets with 5'-deoxypyridoxal, an effective inhibitor of GDH, reduced the islet GDH activity at concentration-dependent manner. Treatment of 5'-deoxypyridoxal up to 2 mM did not affect the cell viability. There was reduction in V(max) values on average about 60%, whereas no changes in K(m) values for substrates and coenzymes were observed. The concentration of GDH on the Western blot analysis and the level of GDH mRNA remained unchanged. The concentration of glutamate decreased by 52%, whereas the concentration of 2-oxoglutarate increased up to 2.3-fold in the presence of 5'-deoxypyridoxal. 5'-Deoxypyridoxal had no effects on inhibition by GTP and activation by ADP or L-leucine of islet GDH. In parallel with the inhibition of GDH activity, perfusion of islets with 5'-deoxypyridoxal reduced insulin release up to 2.5-fold. Although precise mechanism for correlation between GDH activity and insulin release remains to be studied further, our results suggest a possibility that the inhibitory effect of 5'-deoxypyridoxal on islet GDH activity may correlate with its effect on insulin release.
Yang
Seung-Ju
SJ
Department of Biochemistry and Molecular Biology, University of Ulsan College of Medicine, 388-1 Poongnap-dong, Songpa-ku, Seoul 138-736, South Korea.
Huh
Jae-Wan
JW
Kim
Mi Jung
MJ
Lee
Woo-Je
WJ
Kim
Tae Ue
TU
Choi
Soo Young
SY
Cho
Sung-Woo
SW
D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D005969:Glutamate Dehydrogenase / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D011730:Pyridoxal / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D007328:Insulin; D006153:Guanosine Diphosphate; C001609:5-deoxypyridoxal; D018698:Glutamic Acid; D011730:Pyridoxal; D000244:Adenosine Diphosphate; D007770:L-Lactate Dehydrogenase; D005969:Glutamate Dehydrogenase