Sequences directing dihydrolipoamide dehydrogenase (E3) binding are located on the 2-oxoglutarate dehydrogenase (E1) component of the mammalian 2-oxoglutarate dehydrogenase multienzyme complex.

Sequences located in the N-terminal region of the high M(r) 2-oxoglutarate dehydrogenase (E1) enzyme of the mammalian 2-oxoglutarate dehydrogenase multienzyme complex (OGDC) exhibit significant similarity with corresponding sequences from the lipoyl domains of the dihydrolipoamide acetyltransferase (E2) and protein X components of eukaryotic pyruvate dehydrogenase complexes (PDCs). Two additional features of this region of E1 resemble lipoyl domains: (i) it is readily released by trypsin, generating a small N-terminal peptide with an apparent M(r) value of 10,000 and a large stable 100,000 M(r) fragment (E1') and (ii) it is highly immunogenic, inducing the bulk of the antibody response to intact E1. This 'lipoyl-like' domain lacks a functional lipoamide group. Selective but extensive degradation of E1 with proteinase Arg C or specific conversion of E1 to E1' with trypsin both cause loss of overall OGDC function although the E1' fragment retains full catalytic activity. Removal of this small N-terminal peptide promotes the dissociation of dihydrolipoamide dehydrogenase (E3) from the E2 core assembly and also affects the stability of E1 interaction. Thus, structural roles which are mediated by a specific gene product, protein X in PDC and possibly also the E2 subunit, are performed by similar structural elements located on the E1 enzyme of the OGDC.     

A review and update of animal toxicoses associated with fumonisin-contaminated feeds and production of fumonisins by Fusarium isolates

During the 1989 corn harvest season, numerous reports of equine leukoencephalomalacia (ELEM) outbreaks and a pulmonary edema (PPE) syndrome in swine from several regions of the United States were received by the National Veterinary Services Laboratories (NVSL), Ames, Iowa. Previous and concurrent research linked Fusarium moniliforme and fumonisin-contaminated feeds to both diseases. Chemical and mycological investigations revealed fumonisin B₁ (FB₁) concentrations of 20 to 360 ppm in suspect swine feeds and 8 to 117 ppm in suspect equine feeds. Nonproblem feeds contained concentrations below 8 ppm. Fusarium moniliforme and Fusarium proliferatum were isolated from both problem and nonproblem equine and swine feeds. When cultured on autoclaved corn, the F. moniliforme and F. proliferatum isolates produced respective FB₁ and fumonisin B₂ (FB₂) that range from less than 5 to more than 2450 ppm and less than 5 to more than 1000 ppm, respectively. Isolates from both problem and nonproblem feeds produced high levels (greater than 500 ppm) in culture. Reported here is a review of chemical and mycological data resulting from the study of several cases of PPE and ELEM.     

Structure and expression of a gene from Arabidopsis thaliana encoding a protein related to SNF1 protein kinase

The AKin10 gene from Arabidopsis thaliana encoding a putative Ser/Thr protein kinase (PK) has been isolated and characterized. The AKin10-encoding gene is located on a genomic 5.4-kb BamHI fragment and contains ten introns, one being located in the 5' untranslated region. The deduced amino acid sequence of AKin10 is 65% identical over the catalytic domain to the yeast PK (SNF1). SNF1 is essential for the derepression of many glucose-repressible genes, including Suc2 which encodes invertase. Southern blot hybridization experiments suggested the presence of one copy of the gene per haploid genome of A. thaliana. Northern hybridization experiments indicated that this gene is expressed in roots, shoots and leaves. AKin10 may play an important role in a signal transduction cascade regulating gene expression and carbohydrate metabolism in higher plants.     

Appetite and growth compensation in the European minnow,Phoxinus phoxinus (Cyprinidae), following short periods of food restriction

Synopsis Changes in the daily appetite and weekly growth rates of individual adult minnows,Phoxinus phoxinus, on ad libitum rations were recorded before and after they had experienced 4 or 16 days of food restriction. Feeding levels during the restriction periods were either starvation or a maintenance ration. The latter was estimated from a previously determined regression model. Water temperature was 15°C and the photoperiod 9L15D in all experiments. The mean weight of fish used ranged from 1.06 to 2.15 g. The 4 day restriction had no detectable effects on appetite or growth. After the 16 day restriction, the minnows showed hyperphagia and had increased specific growth rates and growth efficiencies compared with control fish. The compensatory increases in appetite and growth were not sustained and within three weeks had declined to levels not significantly different from those of the control fish. At the end of the experiments, there were no significant differences between the mean weights or cumulative food consumption of the restricted and control groups. The results suggest that adult minnows regulate their appetite and growth rate in relation to their previous nutritional history.     

Capture and allocation of nitrogen byQuercus douglasii seedlings in competition with annual and perennial grasses

Summary The spatial overlap of woody plant root systems and that of annual or perennial grasses promotes competition for soil-derived resources. In this study we examined competition for soil nitrogen between blue oak seedlings and either the annual grassBromus mollis or the perennial grassStipa pulchra under controlled outdoor conditions. Short-term nitrogen competition was quantified by injecting¹⁵N at 30 cm depth in a plane horizontal to oak seedling roots and that of their neighbors, and calculating¹⁵N uptake rates, pool sizes and¹⁵N allocation patterns 24 h after labelling. Simultaneously, integrative nitrogen competition was quantified by examining total nitrogen capture, total nitrogen pools and total nitrogen allocation.Stipa neighbors reduced inorganic soil nitrogen content to a greater extent than didBromus plants. Blue oak seedlings responded to lower soil nitrogen content by allocating lower amounts of nitrogen per unit of biomass producing higher root length densities and reducing the nitrogen content of root tissue. In addition, blue oak seedlings growing with the perennial grass exhibited greater rates of¹⁵N uptake, on a root mass basis, compensating for higher soil nitrogen competition inStipa neighborhoods. Our findings suggest that while oak seedlings have lower rates of nitrogen capture than herbaceous neighbors, oak seedlings exhibit significant changes in nitrogen allocation and nitrogen uptake rates which may offset the competitive effect annual or perennial grasses have on soil nitrogen content.     

Probing the opioid receptor complex with (+)-trans-superfit. I. Evidence that [D-Pen2,D-Pen5]enkephalin interacts with high affinity at the delta cx binding site.

A variety of data support the existence of an opioid receptor complex composed of distinct but interacting mu cx and delta cx binding sites, where "cx" indicates "in the complex." The ability of subantinociceptive doses of [Leu5]enkephalin and [Met5]enkephalin to potentiate and attenuate morphine-induced antinociception, respectively, is thought to be mediated via their binding to the delta cx binding site. [D-Pen2,D-Pen5]Enkephalin also modulates morphine-induced antinociception, but has very low affinity for the delta cx binding site in vitro. In the present study, membranes were depleted of their delta ncx binding sites by pretreatment with the site-directed acylating agent, (3S,4S)-(+)-trans-N-[1-[2-(4-isothiocyanato)phenyl)-ethyl]-3-methy l-4- piperidyl]-N-phenylpropaneamide hydrochloride, which permits selective labeling of the delta cx binding site with [3H][D-Ala2,D-Leu5]enkephalin. The major findings of this study are that with this preparation of rat brain membranes: a) there are striking differences between the delta cx and mu binding sites; and b) both [D-Pen2,D-Pen5]enkephalin and [D-Pen2,L-Pen5]enkephalin exhibit high affinity for the delta cx binding site.     

Functional torque-velocity and power-velocity characteristics of elite athletes

Technical limitations of some isokinetic dynamometers have called into question the validity of some data on human muscle mechanics. The Biodex dynamometer has been shown to minimize the impact artefact while permitting automatic gravity correction. This dynamometer was used to study quadriceps muscle torque and power generation in elite power (n = 6) and elite endurance (n = 7) athletes over 12 randomly assigned isokinetic velocities from 30 degrees.s-1 to 300 degrees.s-1. The angle at peak torque varied as a negative, linear function of angular velocity, with the average angle across test velocities being 59.5 degrees (SD 10.2 degrees). Power athletes developed greater peak torque at each angular velocity (P less than 0.05) and experienced a 39.7% decrement in torque over the velocity range tested. Endurance athletes encountered a 38.8% decline in peak torque. Torques measured at 60 degrees of knee flexion followed a similar trend in both groups; however the greatest torques were recorded at 60 degrees.s-1 rather than at 30 degrees.s-1. Leg extensor muscle power increased monotonically with angular velocity in both power (r2 = 0.728) and endurance athletes (r2 = 0.839); however these curves diverged significantly so that the power athletes produced progressively more power with each velocity increment. These inter group differences probably reflected a combination of natural selection and training adaptation.     

A high melting structure in DNA distinguishes phases of the cell cycle

Differential scanning microcalorimetry of the nuclei of dividing CHO cells revealed DNA structures that showed structural transitions at 60, 76, 88, and 105 degrees C (transitions I to IV, respectively). In cultures synchronized by isoleucine deprivation the enthalpies of transitions I and II were rather constant throughout the cell cycle. While the sum of the enthalpies of III and IV was nearly constant, the ratio of IV to III varied substantially from one phase of the cycle to another. A high IV:III ratio of 6 characterized G1 while S phase gave a IV:III ratio of about 2. Cells containing metaphase chromosomes also showed a IV:III ratio near 2. The IV:III ratio for CHO cells showed a progressive decrease as the cells were maintained in isoleucine-free medium from 0 to 6 days.     

DNA polymerase I activity in Escherichia coli is influenced by spot 42 RNA.

We have shown that the level of DNA polymerase I (Pol I) activity in Escherichia coli is influenced by the level of a 109-nucleotide RNA, spot 42 RNA. Deletion of the gene for spot 42 RNA results in a 20 to 25% decrease in Pol I activity, as assayed by nucleotide incorporation in cell extracts and a decrease in the ability of cells to grow in the presence of the DNA-alkylating agent methyl methanesulfonate. Also, a physiological reduction of the level of spot 42 RNA, by growth in media containing poor carbon sources, results in a corresponding decrease in Pol I activity. Conversely, overproduction of spot 42 RNA results in a 10 to 15% increase in Pol I activity in vitro. Thus, changes in the amount of spot 42 RNA result in relatively small but significant changes in Pol I activity.