Biosynthesis and import into the mitochondrion of L-3-glycerophosphate dehydrogenase, and the effect of thyroid hormone deficiency on gene expression.

Mitochondrial L-3-glycerophosphate dehydrogenase (EC 1.1.99.5) is synthesised in bovine kidney (NBL-1) cells treated with uncoupler as a cytosolic precursor with Mr = 76,000 indistinguishable from the mature form. In vitro translation of rat liver mRNA also gives rise to a product of Mr = 76,000 but when this is imported into mitochondria it is processed to a product of Mr = 66,000. L-3-Glycerophosphate dehydrogenase activity and immunoreactive protein are greatly decreased in liver mitochondria from hypothyroid rats. Paradoxically, in vitro translation of the mRNA from such animals gives rise to large amounts of the protein, much greater than that synthesised from euthyroid mRNA and comparable with that produced from hyperthyroid mRNA.