Pitfalls in the molecular genetic diagnosis of Leber hereditary optic neuropathy (LHON).

Pathogenetic mutations in mtDNA are found in the majority of patients with Leber hereditary optic neuropathy (LHON), and molecular genetic techniques to detect them are important for the diagnosis. A false-positive molecular genetic error has adverse consequences for the diagnosis of this maternally inherited disease. We found a number of mtDNA polymorphisms that occur adjacent to known LHON-associated mutations and that confound their molecular genetic detection. These transition mutations occur at mtDNA nt 11779 (SfaNI site loss, 11778 mutation), nt 3459 (BsaHI site loss, 3460 mutation), nt 15258 (AccI site loss, 15257 mutation), nt 14485 (mismatch primer Sau3AI site loss, 14484 mutation), and nt 13707 (BstNI site loss, 13708 mutation). Molecular genetic detection of the most common pathogenetic mtDNA mutations in LHON, using a single restriction enzyme, may be confounded by adjacent polymorphisms that occur with a false-positive rate of 2%-7%.     

Hydrolysis of bile acid conjugates by selected fungi

Summary Fungi which have been previously shown to hydrolyse glycocholic acid, with liberation of the free bile acid, have now been shown to be similarly capable of hydrolysing glycodeoxycholic acid. Sodium taurocholate, however, is much less susceptible and its hydrolysis has been demonstrated with only one of the selected fungi, Penicillium chrysogenum, growing in a medium containing the conjugate as the sole sulphur source. It is concluded that the nature of the amino acid moiety is important in determining the ease of hydrolysis of bile acid conjugates by whole cells of the fungi under test.     

Monolayer properties of chloroplast lipids

The properties of seven monogalactosyldiacylglycerols and six digalactosyldiacylglycerols, isolated from photosynthetic membranes and possessing different levels of fatty acid unsaturation, have been studied by the monolayer technique and compared with those of the fully saturated compounds. In addition, the monolayer properties of sulphoquinovosyldiacylglycerols and phosphatidylglycerols from higher plant chloroplasts, and several hexadecenoic acids have been measured.Monogalactosyldiacylglycerols containing saturated fatty acids form a condensed monolayer similar to that of saturated phosphatidylcholines. The naturally occurring monogalactosyldiacylglycerols, of which the double bond index ranged from 0.6 to 3.9, possessed comparable force-area curves suggesting that headgroup interactions play a more important role in packing behaviour than in phosphatidylcholines. Although digalactosyldiacylglycerols containing fully saturated fatty acids form a more expanded monolayer than the corresponding monogalactosyldiacylglycerols, the degree of expansion of the monolayer due to the presence of unsaturated fatty acids in the naturally occurring digalactosyldiacylglycerols is much less than in monogalactosyldiacylglycerols. Monogalactosyldiacylglycerols and digalactosyldiacylglycerols from a single species have very similar monolayer properties, and the presence of sulphoquinovosyldiacylglycerols and phosphatidylglycerols in the proportions in which they occur in higher plant chloroplasts does not have any condensing effect on a monolayer of galactolipids     

Receptor kinetics differ for endothelin-1 and endothelin-2 binding to Swiss 3T3 fibroblasts

The equilibrium binding, kinetics of ligand-receptor interactions, and biological activity of endothelin-1 and -2 have been studied in Swiss 3T3 fibroblasts. Scatchard analyses of saturation binding data for ET-1 and -2, performed at 4 degrees C to prevent internalization of the occupied receptor, revealed similar affinity constants and numbers of binding sites for endothelin-1 and -2. Experiments designed to determine ligand-induced effects on 45Ca efflux demonstrated no qualitative or quantitative differences between the two endothelin isoforms. In contrast, kinetic studies resulted in different rates of dissociation for the two isoforms and different extents of dissociation. Specifically, only 40% of the bound [125I]endothelin-1 was dissociated at 4 h following the addition of excess unlabeled ligand, whereas 85-90% of the bound [125I]endothelin-2 was dissociated under the same conditions. Endothelin-1 and -2 also differed in the percent of specific cell-associated ligand bound after a 2 h incubation at 37 degrees C following an initial equilibration at 4 degrees C. The differences in dissociation rates and association or internalization rates at 37 degrees C are the first data that differentiate between the two isoforms. It is suggested that isoform-specific differences in the rate of dissociation from cell surface endothelin receptors influence the level of cell-associated endothelin and may be important in determining physiologic responses in vivo.     

Interaction of Triton X-100 with particulate cardiac guanylate cyclase: comparison between Mg2+- and Mn2+-supported enzyme activities in particulate. detergent-solubilized and detergent-insoluble fractions

Guanylate cyclase activity was determined in a 1000g particulate fraction derived from rabbit heart homogenates using Mg²⁺ or Mn²⁺ as sole cation in the presence and absence of Triton X-100. With Mg²⁺, very little guanylate cyclase activity could be detected in the original particulate fraction assayed with or without Triton, or in the particulate fraction treated with varying concentrations of Triton (detergent-treated mixture) prior to enzyme assay. However, the detergent-solubilized supernatants as well as the detergent-insoluble residues (pellets) derived from detergent-treated mixtures possessed appreciable Mg²⁺-supported enzyme activity. With Mn²⁺, significant enzyme activity was detectable in the original particulate fraction assayed without Triton. Much higher activity was seen in particulate fraction assayed with Triton and in detergent-treated mixtures; the supernatants but not the pellets derived from detergent-treated mixtures possessed even greater activity. The sum of enzyme activity in pellet and supernatant fractions greatly exceeded that of the mixture. When the pellets and supernatants derived from detergenttreated mixtures were recombined, measured enzyme activities were similar to those of the original mixture. With Mg²⁺ or Mn²⁺, the specific activity of guanylate cyclase in pellet and supernatant fractions varied considerably depending on the concentration of Triton used for treatment of the particulate fraction; treatment with low concentrations of Triton (0.2–0.7 μmol/mg protein) gave supernatants showing high activity whereas treatment with relatively greater concentrations of the detergent (>0.7 μmol/mg protein) gave pellets showing high activity. The relative distribution of guanylate cyclase in pellet and supernatant fractions expressed as a function of Triton concentration during treatment (of the particulate fraction) showed that 50 to 80% of the recovered enzyme activity remained in supernatants at low detergent concentrations whereas 50 to 80% of the recovered activity resided in the pellets at higher detergent concentrations. Inclusion of excess Triton in the enzyme assay medium did not alter the specific activity profiles and the relative distribution patterns of the cyclase in pellet versus supernatant fractions. The results demonstrate the inherent potential of cardiac particulate guanylate cyclase to utilize Mg²⁺ in catalyzing the synthesis of cyclic GMP. However, it appears that some factor(s) endogenous to the cardiac particulate fraction severely impairs the expression of Mg²⁺-dependent activity; Mn²⁺-dependent activity is also affected by such factor(s) but apparently less severely. Further, the results suggest that previously reported activities of cardiac particulate guanylate cyclase, despite being assayed with Mn²⁺ and in the presence of Triton X-100, represent underestimation of what otherwise appears to be a highly active enzyme system capable of utilizing physiologically relevant divalent cation such as Mg²⁺.     

The effect of indomethacin and substance P on the guinea pig urinary bladder

The effects of indomethacin on the responses of the guinea pig urinary bladder to nerve stimulation, acetylcholine, adenosine 5′ triphosphate and Substance P have been investigated. Indomethacin alone had no significant effect on responses of the bladder to nerve stimulation but did significantly reduce the atropine-resistant contractions. Responses of the tissue to acetylcholine were unaffected by indomethacin but responses to Substance P were significantly reduced. Only the highest dose of ATP (10^?3 M) was significantly reduced by indomethacin. The possibility that Substance P is the transmitter responsible for the atropine-resistant contractions of the urinary bladder to nerve stimulation is discussed.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.