Nitric oxide inhibits cardiac energy production via inhibition of mitochondrial creatine kinase.
Nitric oxide biosynthesis in cardiac muscle leads to a decreased oxygen consumption and lower ATP synthesis. It is suggested that this effect of nitric oxide is mainly due to the inhibition of the mitochondrial respiratory chain enzyme, cytochrome c oxidase. However, this work demonstrates that nitric oxide is able to inhibit soluble mitochondrial creatine kinase (CK), mitochondrial CK bound in purified mitochondria, CK in situ in skinned fibres as well as the functional activity of mitochondrial CK in situ in skinned fibres. Since mitochondrial isoenzyme is functionally coupled to oxidative phosphorylation, its inhibition also leads to decreased sensitivity of mitochondrial respiration to ADP and thus decreases ATP synthesis and oxygen consumption under physiological ADP concentrations. (+info
Kinetics of transhydrogenase reaction catalyzed by the mitochondrial NADH-ubiquinone oxidoreductase (Complex I) imply more than one catalytic nucleotide-binding sites.
The steady-state kinetics of the transhydrogenase reaction (the reduction of acetylpyridine adenine dinucleotide (APAD+) by NADH, DD transhydrogenase) catalyzed by bovine heart submitochondrial particles (SMP), purified Complex I, and by the soluble three-subunit NADH dehydrogenase (FP) were studied to assess a number of the Complex I-associated nucleotide-binding sites. Under the conditions where the proton-pumping transhydrogenase (EC 220.127.116.11) was not operating, the DD transhydrogenase activities of SMP and Complex I exhibited complex kinetic pattern: the double reciprocal plots of the velocities were not linear when the substrate concentrations were varied in a wide range. No binary complex (ping-pong) mechanism (as expected for a single substrate-binding site enzyme) was operating within any range of the variable substrates. ADP-ribose, a competitive inhibitor of NADH oxidase, was shown to compete more effectively with NADH (Ki = 40 microM) than with APAD+ (Ki = 150 microM) in the transhydrogenase reaction. FMN redox cycling-dependent, FP catalyzed DD transhydrogenase reaction was shown to proceed through a ternary complex mechanism. The results suggest that Complex I and the simplest catalytically competent fragment derived therefrom (FP) possess more than one nucleotide-binding sites operating in the transhydrogenase reaction. (+info
Identity of heart and liver L-3-hydroxyacyl coenzyme A dehydrogenase.
Rat heart and liver cDNAs for precursor of L-3-hydroxyacyl-CoA dehydrogenase have been cloned and sequenced. The results indicate that these different rat organs express identical dehydrogenases. Furthermore, pig heart mRNA for L-3-hydroxyacyl-CoA dehydrogenase precursor was amplified by reverse transcription-polymerase chain reaction, and all the cDNA clones were found to encode a precursor of liver L-3-hydroxyacyl-CoA dehydrogenase (X.-Y. He, S.-Y. Yang, Biochim. Biophys. Acta 1392 (1998) 119-126) but not the well-documented heart form of the dehydrogenase (K.G. Bitar et al., FEBS Lett. 116 (1980) 196-198). Sequencing data and other evidence establish that the pig, like the rat, has the same dehydrogenase in heart and liver. Since the size and structure of pig heart L-3-hydroxyacyl-CoA dehydrogenase are identical to the pig liver dehydrogenase, reports that relied on the published sequence of the pig heart dehydrogenase need to be re-evaluated. For example, the signature pattern of the L-3-hydroxyacyl-CoA dehydrogenase family is HXFXPX3MXLXE. Furthermore, the published crystal structure of the pig heart dehydrogenase that substantiated each subunit comprising 307 residues with a mercury-binding residue at position 204 (J.J. Birktoft et al., Proc. Natl. Acad. Sci. U.S.A. 84 (1987) 8262-8266) must be re-examined in accordance with this revelation. (+info
Identification of cis-9,10-methylenehexadecanoic acid in submitochondrial particles of bovine heart.
Submitochondrial particles of bovine heart were hydrolyzed by phospholipase A2 and the products were analyzed by liquid chromatography electrospray ionization-mass spectrometry. We found a fatty acid with a molecular mass of 268 Da and a retention time longer than that of linoleic acid. Next, we synthesized organically cis-9,10-methylenehexadecanoic acid, which has a molecular mass similar to that of the extracted fatty acid, and characterized its high performance liquid chromatography and gas chromatography-mass spectrometry profiles. Using these data we were able to identify endogenous cis-9,10-methylenehexadecanoic acid in rat and human heart and liver tissues that had been hydrolyzed by phospholipase A2. This fatty acid was not detected in tissue extracts that had not been hydrolyzed by phospholipase A2. Similar amounts of cis-9, 10-methylenehexadecanoic acid were measured in tissue extracts after total hydrolysis. These results suggest that cis-9, 10-methylenehexadecanoic acid is a fatty acid component, in the sn-2 position, of phospholipids in some mammalian tissue. (+info
Rat liver GTP-binding proteins mediate changes in mitochondrial membrane potential and organelle fusion.
The variety of mitochondrial morphology in healthy and diseased cells can be explained by regulated mitochondrial fusion. Previously, a mitochondrial outer membrane fraction containing fusogenic, aluminum fluoride (AlF4)-sensitive GTP-binding proteins (mtg) was separated from rat liver (J. D. Cortese, Exp. Cell Res. 240: 122-133, 1998). Quantitative confocal microscopy now reveals that mtg transiently increases mitochondrial membrane potential (DeltaPsi) when added to permeabilized rat hepatocytes (15%), rat fibroblasts (19%), and rabbit myocytes (10%). This large mtg-induced DeltaPsi increment is blocked by fusogenic GTPase-specific modulators such as guanosine 5'-O-(3-thiotriphosphate), excess GTP (>100 microM), and AlF4, suggesting a linkage between DeltaPsi and mitochondrial fusion. Accordingly, stereometric analysis shows that decreasing DeltaPsi or ATP synthesis with respiratory inhibitors limits mtg- and AlF4-induced mitochondrial fusion. Also, a specific G protein inhibitor (Bordetella pertussis toxin) hyperpolarizes mitochondria and leads to a loss of AlF4-dependent mitochondrial fusion. These results place mtg-induced DeltaPsi changes upstream of AlF4-induced mitochondrial fusion, suggesting that GTPases exert DeltaPsi-dependent control of the fusion process. Mammalian mitochondrial morphology thus can be modulated by cellular energetics. (+info
Molecular cloning of cDNA encoding mitochondrial very-long-chain acyl-CoA dehydrogenase from bovine heart.
AIM: To clone the cDNA encoding an isoenzyme of mitochondrial very-long-chain acyl-CoA dehydrogenase (VLCAD) from bovine heart lambda gt11 and lambda gt10 cDNA libraries. METHODS: The clone was isolated with immunoscreening technique and validated by (1) the microsequences of the N-terminus and three internal proteolytic fragments from the purified enzyme; (2) identification of the acyl-CoA dehydrogenase (AD) signature sequence; and (3) high homology of the deduced peptide sequences, as expected, with those of rat liver mitochondrial VLCAD. RESULTS: The cDNA (2203 bp) corresponds to a approximately 2.4-kb mRNA band from the same tissue source revealed by a Northern blotting. The deduced peptide sequence of 655 amino acids (70,537 Da) is composed of a 40-amino acid mitochondrial leader peptide moiety (4,346 Da) and a 615-amino acid peptide as a mature protein (66,191 Da). A comparison of the peptide sequences in the AD family shows the major diversity in their signal sequences, suggesting a structural basis for their different mitochondrial locations. The catalytic sites are all highly conserved among VLCAD. Ser-251 analogous to and Cys-215 diversified to other family members. A pseudo-consensus sequence of leucine zipper was found in the C-terminal region from Leu-568 to Leu-589, implying a mechanism whereby the dimer of this protein is formed by zipping these leucine residues from the alpha-helixes of 2 monomers. CONCLUSION: The isolated cDNA clone encodes an isoenzyme of mitochondrial VLCAD in bovine heart. (+info
Rapid progression of cardiomyopathy in mitochondrial diabetes.
Cardiac involvement and its clinical course in a diabetic patient with a mitochondrial tRNA(Leu)(UUR) mutation at position 3243 is reported in a 54-year-old man with no history of hypertension. At age 46, an electrocardiogram showed just T wave abnormalities. At age 49, it fulfilled SV1 + RV5 or 6>35 mm with strain pattern. At age 52, echocardiography revealed definite left ventricular (LV) hypertrophy, and abnormally increased mitochondria were shown in biopsied endomyocardial specimens. He was diagnosed as having developed hypertrophic cardiomyopathy associated with the mutation. However, at age 54, SV1 and RV5,6 voltages were decreased, and echocardiography showed diffuse decreased LV wall motion and LV dilatation. Because he had mitochondrial diabetes, the patient's heart rapidly developed hypertrophic cardiomyopathy, and then it seemed to be changing to a dilated LV with systolic dysfunction. Rapid progression of cardiomyopathy can occur in mitochondrial diabetes. (+info
Identification of quinone-binding and heme-ligating residues of the smallest membrane-anchoring subunit (QPs3) of bovine heart mitochondrial succinate:ubiquinone reductase.
The smallest membrane-anchoring subunit (QPs3) of bovine heart succinate:ubiquinone reductase was overexpressed in Escherichia coli JM109 as a glutathione S-transferase fusion protein using the expression vector pGEX2T/QPs3. The yield of soluble active recombinant glutathione S-transferase-QPs3 fusion protein was isopropyl-1-thio-beta-D-galactopyranoside concentration-, induction growth time-, temperature-, and medium-dependent. Maximum yield of soluble recombinant fusion protein was obtained from cells harvested 3.5 h post-isopropyl-1-thio-beta-D-galactopyranoside (0.4 mM)-induction growth at 25 degrees C in 2.0% tryptone, 0.5% yeast extract, 10 mM NaCl, 2.5 mM KCl, 10 mM MgCl2, 20 mM glucose (SOC medium) containing 440 mM sorbitol and 2.5 mM betaine. QPs3 was released from the fusion protein by proteolytic cleavage with thrombin. Isolated recombinant QPs3 shows one protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis that corresponds to subunit V of mitochondrial succinate:ubiquinone reductase. Although purified recombinant QPs3 is dispersed in 0.01% dodecylmaltoside, it is in a highly aggregated form, with an apparent molecular mass of more than 1 million. The recombinant QPs3 binds ubiquinone, causing a spectral blue shift. Upon titration of the recombinant protein with ubiquinone, a saturation behavior is observed, suggesting that the binding is specific and that recombinant QPs3 may be in the functionally active state. Two amino acid residues, serine 33 and tyrosine 37, in the putative ubiquinone binding domain of QPs3 are involved in ubiquinone binding because the S33A- or Y37A-substituted recombinant QPs3s do not cause the spectral blue shift of ubiquinone. Although recombinant QPs3 contains little cytochrome b560 heme, the spectral characteristics of cytochrome b560 are reconstituted upon addition of hemin chloride. Reconstituted cytochrome b560 in recombinant QPs3 shows a EPR signal at g = 2.92. Histidine residues at positions 46 and 60 are responsible for heme ligation because the H46N- or H60N-substituted QPs3 fail to restore cytochrome b560 upon addition of hemin chloride. (+info