Impaired ATP synthase assembly associated with a mutation in the human ATP synthase subunit 6 gene

Mutations in human mitochondrial DNA are a well recognized cause of disease. A mutation at nucleotide position 8993 of human mitochondrial DNA, located within the gene for ATP synthase subunit 6, is associated with the neurological muscle weakness, ataxia, and retinitis pigmentosa (NARP) syndrome. To enable analysis of this mutation in control nuclear backgrounds, two different cell lines were transformed with mitochondria carrying NARP mutant mitochondrial DNA. Transformant cell lines had decreased ATP synthesis capacity, and many also had abnormally high levels of two ATP synthase sub-complexes, one of which was F(1)-ATPase. A combination of metabolic labeling and immunoblotting experiments indicated that assembly of ATP synthase was slowed and that the assembled holoenzyme was unstable in cells carrying NARP mutant mitochondrial DNA compared with control cells. These findings indicate that altered assembly and stability of ATP synthase are underlying molecular defects associated with the NARP mutation in subunit 6 of ATP synthase, yet intrinsic enzyme activity is also compromised.

Separation of intact pyruvate dehydrogenase complex using blue native agarose gel electrophoresis

We show that the blue native gel polyacrylamide electrophoresis system (BN-PAGE) can be applied to pyruvate dehydrogenase complex (PDC). BN-PAGE has been used extensively to study the multisubunit enzymes of oxidative phosphorylation, as nondenaturing separation in the first dimension maintains holoenzyme integrity. However, the standard protocol was inappropriate for PDC as, at 10 MDa, it is approximately ten times larger than the largest respiratory chain enzyme complex. Therefore, agarose was substituted for polyacrylamide. Moreover, a substantial decrease in salt concentration was necessary to prevent dissociation of PDC. As with standard BN-PAGE, immunoblots of second-dimensional sodium dodecyl sulfate-PAGE (SDS-PAGE) provided more detailed information on specific subunits and subcomplexes. The method was applied to human heart mitochondrial fragments, control cultured human cells, rho0 cells that lack mitochondrial DNA, and two cell lines derived from patients with PDC deficiency. The PDC deficient cell lines showed a clear correlation between amount of PDC holoenzyme and disease severity. In cells lacking mitochondrial DNA, synthesis and assembly of all PDC subunits (all nuclearly encoded) appeared normal, suggesting that respiratory function has no regulatory role in PDC biogenesis. Blue native agarose gel electrophoresis coupled with standard second-dimensional SDS-PAGE provides a new tool to be used in conjunction with biochemical assays and immunoblots of one-dimensional SDS-PAGE to further elucidate the nature of PDC in normal and disease states. Furthermore, other cellular protein complexes of 1 MDa or more can be analysed by this method.

From sequence to chromosome: the tip of the X chromosome of D. melanogaster

One of the rewards of having a Drosophila melanogaster whole-genome sequence will be the potential to understand the molecular bases for structural features of chromosomes that have been a long-standing puzzle. Analysis of 2.6 megabases of sequence from the tip of the X chromosome of Drosophila identifies 273 genes. Cloned DNAs from the characteristic bulbous structure at the tip of the X chromosome in the region of the broad complex display an unusual pattern of in situ hybridization. Sequence analysis revealed that this region comprises 154 kilobases of DNA flanked by 1.2-kilobases of inverted repeats, each composed of a 350-base pair satellite related element. Thus, some aspects of chromosome structure appear to be revealed directly within the DNA sequence itself.

Cholinesterase in muscle of dystrophic hamsters (Bio-40.54)

Isozyme patterns of cholinesterase (ChE) from heart, tongue, and skeletal muscle of normal and dystrophic hamsters are presented. Two principal bands, bands 1 and 2, were evaluated. Band 1 migrates faster towards the anode than does band 2. While bands 1 and 2 stain for AChE and were found in control muscles, only band 2 was stained by a pseudocholinesterase (BuChE) and was decreased in samples from dystrophic hamsters. The decrease in BuChE was most pronounced in dystrophic heart muscle. The low level of BuChE measured for dystrophic animal tissue was similar to isozyme patterns found in embryonic tissue and in denervated muscle. BuChE obtained by acrylamide gel electrophoresis along with 16S AchE appears to be a useful biochemical marker of nerve-muscle interactions.

Development of an improved tracheal explant bioassay for the detection of the ciliary dyskinesia factor in cystic fibrosis serum

A tracheal ring explant system, when used with 25% cystic fibrosis (CF) serum, displayed obvious ciliostasis. Hamster, rabbit, and guinea pig explants all had measurable decreases in ciliary activity after 24 hr of incubation in the serum. The differential response to CF serum (relative to normal serum) was greatly increased by using explants which were maintained 24-72 hr in minimal essential medium (MEM) with 10% horse serum and which were selected on the basis of optimal ciliary activity and vigor. With such a bioassay system of guinea pig tracheal explants, incubation with 25% normal serum would produce essentially no change in relative ciliary activity (score of 242 of a possible 300), whereas CF serum resulted in an 86% decrease (score of 33). Scanning electron microscopic observation indicated that the explants displaying the CF-ciliostatic effect had significant accumulations of mucous over the ciliated epithelial surface. A biochemical viability assay (dehydrogenase activity) showed no cytonecrosis when CF serum-treated tissues were compared to standard explants (10% horse serum in MEM) or control explants (25% normal human serum).

Acetylcholinesterase isozymes in developing mouse tissues

Several isozymes of acetylcholinesterase are separated by 10% acrylamide gel electrophoresis of mouse blood, brain, heart, muscle and tongue tissues. Two isozymes migrating near the origin are described which show changes in relative activity during development. The faster of the two bands is proportionately higher in concentration in embryonic tissues and is highly specific for the acetylthiocholine iodide substrate. This isozyme corresponds to the erythrocyte membrane AChE in electrophortic mobility and substrate specificity. The slower of the two bands is predominant in adult tissues and exhibits considerable cross reaction with the butyrylthiocholine iodide substrate. During embryonic and postnatal developmental stages there is a gradual shift from the faster migrating isozyme toward a predominance of the slower migrating isozyme.