THE AMINO-ACID-SEQUENCE OF THE PANCREATIC-ISLET MITOCHONDRIAL GLYCEROL PHOSPHATE DEHYDROGENASE IS NOT UNIQUE AND THE ENZYME IS NOT THYROID OR GLUCOSE RESPONSIVE

The mitochondrial glycerol phosphate dehydrogenase (mGPD) is one of several proteins that are abundant in the pancreatic islet. Hormonal and nutritional influences confer tissue-specific patterns of expression on many of these proteins and the primary amino acid sequence of these proteins in the islet often differs from those in other tissues. However, the deduced amino acid sequence of the rat islet mGPD was identical to that of testis and liver. (The islet mGPD also possesses calmodulin-like calcium-binding sequences.) Islet mGPD activity and amount of protein were not changed by culturing islets at various concentrations of the insulin secretagogues, glucose, leucine, glutamine, or methyl succinate, which are conditions that alter the amounts of other enzymes in the islet. Unlike mGPD in tissues, such as liver, where mGPD activity is low, the high amount of islet mGPD was not further induced in hyperthyroid rats or by adding T-3 to cultured islets or rat insulinoma cells. This suggests that the islet mGPD is under different regulation than the enzyme in tissues where its activity is low. (C) 1995 Academic Press, Inc.