A C5'-centred deoxyribose radical in single crystals of 5-chloro-and 5-bromodeoxyuridine X-irradiated at low temperatures.

X-irradiation at 77 K and subsequent warming to 150 K of single crystals of 5-chloro-and 5-bromodeoxyuridine produces a radical located at position C5' of the deoxyribose moiety. The radical exhibits identical spectral properties in both crystal systems. It is characterized by interaction of the unpaired electron with an alpha-proton(-17-0, -8-7, -33-7G), a beta-proton (18-6, 21-3, 17-5 G) as well as an OH-proton (4-8, 7-9, 12-8 G). The principal values of the g-tensor are 2-0034, 2-0049 and 2-0042. The spectral parameters are discussed in relation to those of the same or similar radicals in other nucleosides (-tides).     

Repair rate in human fibroblasts measured by thymine dimer excorporation

Summary The UV photoproduct, thymine dimer ( ), is excorporated with a remarkably low rate from the DNA of human fibroblasts grown in cell culture. An UV dose of 18 J/m² creates 0.045% (related to thymine). Within the first two days of repair logarithmically growing and quiescent fibroblasts exhibit the same repair rates; thereafter, the proportion of is lower in growing cells due to recovery of DNA replication. Only about 50% of the lesions are excised within 24 h. In quiescent cells, 13% of the thymine dimers originally present can be detected as late as a week after UV-irradiation. Two distinct first-order rate constants indicate that approximately half of the dimers are less accessible to repair. Repair measured by the nucleoid decondensation technique corresponds to the faster repair rate, whereas the slow repair rate cannot be detected by this method. Saturation of repair is found beyond 27 J/m². The remarkably slow rate of excision indicates that thymine dimers are not lethal lesions in human fibroblasts.     

Morphological adaptations of benthic invertebrates to stream flow — An old question studied by means of a new technique (Laser Doppler Anemometry)

Summary The generally accepted concept that dorsoventral flatness and/or small size of benthic stream invertebrates staying on the surface of the bottom substratum allows a current-sheltered life in the boundary layer (Ambühl 1959) is checked by means of the new technique of Laser Doppler Anemometry (LDA). With LDA measurement of flow can be done nearly punctually without any mechanical disturbance. Mapping the current velocities around the body of Ecdyonurus cf. venosus (Insecta, Ephemeroptera) and Ancylus fluviatilis (Gastropoda) gives evidence that boundary layer separation occurs above the animals' bodies. Our results indicate that the velocities around the body of benthic stream invertebrates and probably the forces acting on them are much more complicate than is suggested by the currently accepted boundary layer concept.     

The 32 S RNA of Neurospora crassa mitochondria is not a precursor of the mitochondrial ribosomal RNAs.

Studies on the synthesis of Neurospora mitochondrial ribosomal RNAs by Kuriyama &; Luck 1973 have led to the currently accepted idea that the mature 19 S and 25 S rRNA species are synthesized via a common 32 S precursor RNA. The present results provide evidence that the 32 S RNA band analyzed by Kuriyama &; Luck was in fact a mixture of low concentrations of rapidly labeled RNA species, probably including separate precursors of 19 S and 25 S RNA, along with higher concentrations of aggregates of mature 19 S and 25 S RNA. The former account for the pulse-labeling characteristics of the 32 S band, whereas the latter contribute most of the mass-label, resulting in misleading hybridization data.     

Monophagie und „subsequent evolution“ in ihrer theoretischen Bedeutung für die Insekt-Pflanze-Beziehung

The term monophagy is applied to animal species which are linked to a single plant-reprospecies at least during part of their ontogeny. Aspects of subsequent evolution of monophagous animal species and their plant host species are discussed.     

Linoleic acid-induced endothelial cell injury: Role of membrane-bound enzyme activities and lipid oxidation

High plasma levels of linoleic acid (18:2) may injure endothelial cells, resulting in decreased barrier function of the vascular endothelium. The effects of linoleic acid on endothelial barrier function (transendothelial movement of albumin), membrane-bound enzyme activities, and possible autooxidation of linoleic acid under experimental conditions were studied. The exposure of endothelial monolayers to 18:2 for 24 hr at 60, 90, and 120 μM. fatty acid concentrations caused a significant increase in transendothelial movement of albumin, with maximum albumin transfer at 90 μM. Fatty acid treatment resulted in the increased appearance of cytosolic lipid droplets. Activities of the membrane-bound enzymes, angiotensin-converting enzyme (ACE), and Ca²⁺-ATPase increased steadily with increasing time of cell exposure to 90 μM 18:2, reaching significance at 24 hr. Treatment of endothelial cultures with up to 120 μM 18:2 did not cause cytotoxicity, as evidenced by a nonsignificant change in cellular release of [₃H]-adenine. Incubation of 18:2-supplemented serum-containing culture media with 1000 μM 18:2 at 37°C for up to 48 hr did not result in formation of autooxidation products. These results suggest that 18:2 itself, and not its oxidation products, plays a major role in disrupting endothelial barrier function.     

The role of Lys272 in the pyridoxal 5-phosphate active site of Synechococcus glutamate-1-semialdehyde aminotransferase.

Glutamate-1-semialdehyde (GSA) aminotransferase catalyzes transfer of the C2 amino group of glutamate 1-semialdehyde to the C1 position to yield the tetrapyrrole precursor 5-aminolevulinate. Based on spectrophotometric and steady-state data, GSA aminotransferase is a B6-containing enzyme which uses a ping-pong bi-bi mechanism described for other aminotransferases. A putative active-site lysine at position 272 of Synechococcus GSA aminotransferase was replaced by Arg, Ile or Glu, and genes encoding the corresponding three site directed mutants were expressed in Escherichia coli. The catalytic competence of the resulting enzymes was determined. The similarity of the absorbance spectra of pyridoxal-P-treated forms of Lys272----Arg, Lys272----Ile, Lys272----Glu with free pyridoxal-P indicates that enzyme-bound pyridoxal-P does not form an internal aldimine in in these three site-directed mutants. Whereas Lys----Ile and Lys----Glu form only stable ketimines and aldimines with GSA and its analogues, addition of these compounds to the pyridoxamine-P and pyridoxal-P forms of Lys----Arg induces slow spectral changes, indicating the catalysis of a half-reaction with GSA, 4,5-dioxovalerate and 4,5-diaminovalerate. 5-Aminolevulinate apparently binds with both coenzyme forms of Lys272----Arg, however significant tautomeric rearrangement is only observed with the pyridoxal-P form. It is suggested that Lys272 is the covalent pyridoxal-P-binding site and that this catalytically active lysine residue channels the overall transamination reaction towards 5-aminolevulinate. The second-half reaction (4,5-diaminovalerate in equilibrium with 5-aminolevulinate) is possibly supported by the formation of an internal aldimine which correctly positions the C4 amino group of 4,5-diaminovalerate relative to the enzyme-bound pyridoxal-P.     

Physiological responses of Uroleucon jaceae (L.) to seasonal changes in the quality of its host plant Centaurea jacea L.: multilevel control of adaptations to the life cycle of the host

Summary Exploiters of short-lived plants have evolved strategies in response to physiological changes that occur during the development of their hosts. The ability to adapt to host quality changes is necessary particularly if the mobility of an animal is poor or risk-constrained. In the plant-aphid system Centaurea jaceae-Uroleucon jaceae, the responses of the aphid to the seasonal changes in its host plant grown in poor and good quality soil were investigated. Coarse- and fine-tuned physiological reactions were observed in discrete aphid generations which were reared on plants grown either in a growth chamber or in a greenhouse. The number of ovarioles and developmental time depended on extrinsic factors (length of photoperiod) not directly related to plant quality. The reproductive investment of the aphids was also independent of their total dry weight. However, within the gonadal system high correlations were found at the embryonic level (e.g. the number of sclerotized embryos or the length of the oldest embryos per ovariole were highly correlated with gonadal dry weight). Aphids which were living on the 4-leaf stage of high-quality host plants showed a significantly higher investment in their gonads than aphids feeding on senescenting hosts. Factor analysis corroborated that aphids reared on poor-quality hosts revealed no grouping of variables measured, whereas those which were reared on high-quality plants showed clustering in respect of somatic (tibia length, dry weight of soma) and gonadal (number of sclerotized and unsclerotized embryos, length of the oldest embryos, ovariole number, gonad dry weight) factors. Three different levels of adaptive response to plant quality are distinguished: individual response to host quality, maternal influences on offspring and response to changes not specific to habitat (photoperiod). These different levels of regulation are thought to enable the aphids to adapt to a host of a given nutritional quality and anticipate deteriorating habitat quality simultaneously. It is concluded that physiological constraints in aphids are only revealed when aphids are exposed to severe nutritional stress for several generations.     

Evidence supporting tight linkage of X-linked Emery-Dreifuss muscular dystrophy to the factor VIII:C gene.

In a large German family with Emery-Dreifuss muscular dystrophy (EDMD) linkage analysis was performed using the factor IX gene (F9), the factor VIII:C gene (F8), the anonymous DNA probe DXS52, and DXS15 as markers. Tight linkage was found between the EDMD locus and the F8 probe (Zmax = 1.19; theta max = 0.00), DXS15 (Zmax = 1.75; theta max = 0.00) and DXS52 (Zmax = 2.26; theta max = 0.00). Weak linkage was found to F9 (Zmax = 0.02; theta max = 0.43). The data from the literature and our results suggest that the gene locus of EDMD is close to F8 (confidence interval theta = 0-0.07). The new linkage data are useful for carrier detection and diagnosis of EDMD patients before onset of major clinical signs.