Coupling of mitochondrial metabolism and protein synthesis in heart mitochondria

Abstract

Although much is now known with regard to the processes of mammalian mitochondrial gene expression, relatively little is known concerning the quantitative regulation of this pathway in response to hormones or other physiological stimuli. In this paper the potential coupling of mitochondrial metabolism to mitochondrial protein synthesis was investigated and the concentration of nucleotides and substrates for optimal translation in isolated rat heart mitochondria was determined. It was demonstrated that optimal isolated heart mitochondrial protein synthesis required the presence of an oxidizable substrate. Of the substrates tested, glutamate (20 mM) supported translation best followed by malate, succinate, and alpha-ketoglutarate, whereas pyruvate supported synthesis poorly. Unlike other recent mammalian mitochondrial systems, the presence of an oxidizable substrate was required for translation even in the presence of medium ATP and an exogenous energy-generating system. Mitochondrial translation also required the presence of adenine nucleotide that could be added as ADP or ATP; however, ATP added above 0.5 mM became progressively inhibitory. As a result, synthesis was supported significantly better by ATP synthesized by the system from added ADP, than by ATP added directly to the system. However, if the phosphorylation of ADP was prevented by limiting the phosphate concentration, ADP itself strongly inhibited mitochondrial protein synthesis. This inhibition appeared to be closely related to the energy charge of the system rather than to absolute levels of ADP, indicating for the first time that mitochondrial translation, like its cytoplasmic counterpart is regulated by energy charge. Last, this system did not require the inhibition of guanine nucleotide or exogenous energy-generating systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Zidovudine Inhibits Thymidine Phosphorylation in the Isolated Perfused Rat Heart

“…When they were fully anesthetized, rats were incised laterally below the diaphragm, the chest cavity was opened, and the heart was rapidly removed and placed in cold saline solution. The hearts were immediately placed on a Langendorff perfusion apparatus and perfused at 37°C by a modified Langendorff procedure, exactly as described previously (25). Briefly, isolated rat hearts were subjected to an initial 10 min of nonrecirculating perfusion with Krebs-Henseleit bicarbonate buffer gassed with 95% O 2 -5% CO 2 and containing 15 mM glucose and the plasma levels of all amino acids.…”

Mitochondrial Biogenesis in Skeletal Muscle in Response to Endurance Exercises

“…This once again illustrates the coordinated response mediated by NRF-1 in the expression of nuclear genes involved in mitochondrial metabolism. Mitochondrial translation, as previously shown for cytoplasmic translation (Hucul et al, 1985), is regulated by the energy charge of the cell and is tightly coupled to mitochondrial oxidative metabolism (McKee et al, 1990).…”

“…Lai & Booth (1990) have shown, in a rat study of similar design, that the increase in mitochondrial content was accompanied by alterations in the cytochrome c mRNA level in some muscles. It is also of interest to note that several studies have shown that mitochondrial transcription and translation are tightly regulated through ATP and ADP concentrations (Gaines et al, 1987;McKee et al, 1990). Taken together, these observations suggest that an altered energetic status of the muscle cell may mediate mitochondrial adaptations in skeletal muscle (Shoubridge et al, 1985;Moerland et al, 1989;Lai & Booth, 1990;Booth & Thomason, 1991;Kushmerick, 1994;.…”

Effect of contractile activity on protein turnover in skeletal muscle mitochondrial subfractions

“…Previous investigations of mitochondrial protein synthesis have established that a high cellular energy state is required for optimal amino acid incorporation into protein (18,26). A prime motive for the use of our contractile activity model was the recognition that an alteration in cellular energy state can occur in skeletal muscle subject to intense 10-Hz contractile activity and that it is readily and rapidly reversible during the recovery period (13).…”