Detection of iron-sulfur center-containing subunits of mitochondrial NADH dehydrogenase by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by high-performance gel permeation chromatography

Soluble NADH dehydrogenase resolved from Complex I of the mitochondrial electron-transfer chain was subjected to gel electrophoresis in the presence of sodium dodecyl sulfate at 4 degrees C, and then the gel was stained for iron with bathophenanthroline disulfonate and thioglycolic acid. The 23,000-dalton subunit was markedly stained, and the 51,000-dalton subunit was also stained, but only slightly. High-performance gel permeation chromatography using an eluant containing 0.1% sodium dodecyl sulfate also demonstrated that these subunits contain an iron-sulfur center: the elution pattern recorded by light absorption at 400 nm gave two peaks corresponding to the positions of the subunits.     

Transmembrane control of laminin, lectin receptors and surface villi in teratocarcinoma-derived endodermal cells

Distribution of laminin on the surface of teratocarcinoma-derived parietal endoderm cells was studied by immuno-histochemical staining of the fixed specimen using affinity-purified anti-laminin antibody. Laminin was distributed on the basal surface of the cells, while treatment either with colchicine or with cytochalasin D (CD) resulted in a severely polarized distribution; laminin was seen only at one end of the cell. Treatment with both the reagents did not cause the severe polarization. Receptors for lectins and cell surface villi were polarized by treatment with CD but not by treatment with colchicine. These results suggest that laminin--or its cell surface receptor--is linked to both microfilament and microtubules and that the mode of transmembrane control for laminin is different from certain other cell surface components of the cells.     

The crystallization of mitochondrial cytochrome oxidase-cytochrome c complex

Conditions are described under which crystals are formed with equimolar complex of mitochondrial cytochrome oxidase and cytochrome c. Characteristic absorption bands of the solubilized crystals could be attributed to the cytochrome oxidase-cytochrome c complex with heme a:c ratio of 2:1. Activity of crystals shows more close heme-heme interaction between two cytochromes than that of the mixture.     

Existence of common homologous elements in the transcriptional regulatory regions of human nuclear genes and mitochondrial gene for the oxidative phosphorylation system.

Our previous study indicated that nuclear protein factors of HeLa cells specifically bind to three nuclear Mt elements, Mt1, Mt3, and Mt4, located in the 5'-flanking regions of the human nuclear genes for cytochrome c1 and for ubiquinone-binding protein, both of which are subunits of mitochondrial cytochrome bc1 complex (Suzuki, H., Hosokawa, Y., Toda, H., Nishikimi, M., and Ozawa, T. (1990) J. Biol. Chem. 265, 8159-8163). In this study, we examined whether the same nuclear factors could recognize a set of the Mt3 and Mt4 elements that were found in the displacement loop and the promoter region of mammalian mitochondrial genomes. Gel retardation experiments disclosed that the same nuclear protein factors specifically bind to those Mt elements in the human mitochondrial genome as well as to the nuclear Mt3 and Mt4 elements of the two genes, and that the coexistence of both the elements is required for the efficient binding. The nuclear protein factors which recognize the Mt elements located in the regulatory regions of the nuclear and mitochondrial genes may play an important role in coordinate expression of the two physically separated genes during mitochondrial biogenesis.     

Glycoprotein-binding site of dystrophin is confined to the cysteine-rich domain and the first half of the carboxy-terminal domain.

Dystrophin, a protein product of the Duchenne muscular dystrophy gene, is thought to associate with the muscle membrane by way of a glycoprotein complex which was co-purified with dystrophin. Here, we firstly demonstrate direct biochemical evidence for association of the carboxy-terminal region of dystrophin with the glycoprotein complex. The binding site is found to lie further inward than previously expected and confined to the cysteine-rich domain and the first half of the carboxy-terminal domain. Since this portion corresponds well to the region that, when missing, results in severe phenotypes, our finding may provide a molecular basis of the disease.     

The growth inhibitory factor that is deficient in the Alzheimer's disease brain is a 68 amino acid metallothionein-like protein

We have purified and characterized the growth inhibitory factor (GIF) that is abundant in the normal human brain, but greatly reduced in the Alzheimer's disease (AD) brain. GIF inhibited survival and neurite formation of cortical neurons in vitro. Purified GIF is a 68 amino acid small protein, and its amino acid sequence is 70% identical to that of human metallothionein II with a 1 amino acid insert and a unique 6 amino acid insert in the NH2-terminal and the COOH-terminal portions, respectively. The antibodies to the unique sequence of GIF revealed a distinct subset of astrocytes in the gray matter that appears to be closely associated with neuronal perikarya and dendrites. In the AD cortex, the number of GIF-positive astrocytes was drastically reduced, suggesting that GIF is down-regulated in the subset of astrocytes during AD.     

Novel myosin isoform in nuclear chain fibers of rat muscle spindles produced in response to endurance swimming.

With the use of myosin adenosinetriphosphatase (ATPase) and immunofluorescence staining methods, the adaptive responses of intrafusal and extrafusal fibers to endurance swimming were studied in frozen sections of rat soleus (SOL) and extensor digitorum longus (EDL) muscles. Glycogen depletion confirmed muscle fatigue at the end of a standardized bout of exercise. No significant age-dependent changes in myosin isoforms were detected in any fibers. The 12-wk training increased type I fibers by 10.9% in the SOL and type IIa fibers in the EDL by 16.6%. In trained muscle sections, both staining methods identified a permuted chain fiber, expressed the same as the myosin isoform in the bag2 fiber. However, no exercise-induced change of myosin isoform profile was found in the bag1 and bag2 fibers. Myosin ATPase (and immunofluorescence) staining showed the percentage of permuted chain fibers increased from 0 to 6.7% (5.6%) after 6 wk of training and to 19.2% (14.1%) after 12 wk of training and that it was still at 6.1% (4.2%) 10 wks after training. A novel myosin isoform may thus be expressed in nuclear chain fibers by repetitive recruitment of muscle spindles.     

Site-directed mutagenesis of glutamine residue of calmodulin. Activation of guanylate cyclase of Tetrahymena plasma membrane

Tetrahymena calmodulin (CaM) differs from mammalian CaM in its ability to activate Tetrahymena guanylate cyclase. Of 12 differences in amino acid sequence, two occur near the carboxyl terminus (Gln-143----Arg and Thr-146----deletion). To investigate the functional significance of the carboxyl-terminal region in activation of the guanylate cyclase, three mutated CaMs were engineered by using cassette mutagenesis of rat CaM cDNA: Gln-143----Arg (CaM.A), Thr-146----deletion (CaM.D), and Gln-143----Arg/Thr-146 deletion (CaM.AD). Recombinant wild type CaM (wCaM), CaM.A, CaM.D, and CaM.AD were indistinguishable in their ability to activate cyclic AMP phosphodiesterase. The two mutated CaMs (CaM.A and CaM.AD) with the Gln-143 replacement activated guanylate cyclase of Tetrahymena plasma membrane in the presence of Ca2+, with the maximal activation being half of that produced by Tetrahymena CaM. In contrast, neither CaM.D nor wCaM could stimulate the cyclase activity. A CaM antagonist, W-7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide), prevented the cyclase activation by either Tetrahymena CaM, CaM.A, or CaM.AD. Thus, we conclude that Arg-143 is in a region of the molecule involved in activation of Tetrahymena guanylate cyclase. The data also suggest that the cyclase activation by Tetrahymena CaM requires complex macromolecular interactions between the entire CaM molecule and the enzyme.     

Differences in liver homogenates from Donryu, Fischer, Sprague-Dawley and Wistar strains of rat in the drug-metabolizing enzyme assay and the salmonella/hepatic S9 activation test

Comparison studies for detecting differences between liver microsome and S9 preparations from 4 strains (Donryu, Fischer, Sprague-Dawley, Wistar) of young male rats were carried out with pretreatment of the animals by inducers such as PCBs and PB plus 5,6-BF. Each microsome fraction was assayed for the enzymic activity of metabolism of model substrates such as aniline, benzophetamine, BP, DMN and 7-ethoxycoumarin. The hepatic S9 sample was also compared, as regards its metabolizing ability to activate 9 pre-mutagens (2AA, AAF, o-AAT, BP, DAB, DMBA, DMN, m-PDA, quinoline) to directly acting mutagens in the Salmonella/hepatic S9 activation test by using TA98, TA100 and TA1537 strains with or without cytochrome P450 inhibitors (SKF-525A, metyrapone, 7,8-benzoflavone).In the enzymic assay with PCBs-induced microsomes, BP hydroxylation revealed a strain-specific difference: the microsomes from Fischer and Wistar rats were more effective for metabolizing BP than those from the other strains of rat. The effect of induction by PB plus 5,6-BF for Fischer rats showed relatively higher enzymic activity in the same induction group. Other microsomes prepared from rats with and without induction by PB plus 5,6-BF did not show a clear-cut strain dependency in the enzymic activities assayed.In the mutation experiments with hepatic S9 samples, the examination of DAB and quinoline revealed a marked strain difference when S9 samples prepared from PCBs-pretreated and PB-plus-5,6-BF-induced rats were used: the S9 sample from Fischer rats was available for activating the two pre-mutagens to directly acting mutagens. No marked difference in the metabolic activation of the remaining 7-pre-mutagens was observed on other S9 preparations.In examinations of mutagenicity activities with the use of three inhibitors, the two S9 preparations made with the two induction methods showed inhibition profiles closely similar to each other. However, there were minor differences in the profiles by these inhibitors.From these findings it was concluded that Fischer rat-liver S9 is useful for detecting mutagens in the metabolic activation test, when induction by PB plus 5,6-BF was used in the Ames Salmonella test.     

Changes in predominant energy substrate after hepatectomy

The changes in the energy substrate utilized by the remnant liver were studied in relation to the changes in the cellular energy status of 25 and 70% hepatectomized rabbits. In 25% hepatectomized rabbits, the energy charge $\text{(}\text{(}\text{ATP}\text{+0.5}\text{ADP}\text{)}\text{(}\text{ATP}\text{+}\text{ADP}\text{+}\text{AMP}\text{)}\text{)}$ level of the remnant liver remained unchanged, the energy substrate of which was predominantly glucose, rather than fatty acid. In contrast, in 70% hepatectomized rabbits, the energy production by the mitochondria was mainly dependent upon fatty acid oxidation at the early period after hepatectomy when the energy charge level decreased remarkably, and then upon glucose oxidation, concomitant with the restoration of the energy charge. It is suggested that the changes in the energy substrate utilized are closely related to those in the energy charge level and the mitochondrial phosphorylative activity of the remnant liver following hepatectomy.