Selection in regulated autocatalytic systems

The paper deals with problems involved in the formation of stable structures in a system, in which processes typical of bimolecular autocatalytical reactions occur when the respective components are directly influenced from the outside. Such systems can arise in biochemical, biological and ecological sphere (see, e.g. Glansdorff and Prigogine 1971; Nicolis and Prigogine 1977; Haken 1977; 1980). It has been shown that a regions of so-called subcritical and supercritical regulation exist, manifested by the fact that the given system component would either persist or disappear. The selection of processes consists in the fact that generally only one solution can be realized from N alternatives as a stable state having the nature of a stable node, or a stable focus. When one of the components is supplied to the system from the exterior in a supercritical amount, the system can be "forced" to produce only that single substance. Thus, the system studied can be considered as a model of a biological filter. The results can also be applied in ecology and biotechnology.     

Temperature-sensitive mutants of MH2 avian leukemia virus that map in the v-mil and the v-myc oncogene respectively.

MH2 is an avian retrovirus that contains the v-mil and v-myc oncogenes. In vitro it transforms chick macrophages that are capable of proliferation in the absence of growth factor. Earlier work showed that v-myc induces macrophage transformation and that v-mil induces the production of chicken myelomonocytic growth factor (cMGF), thus generating an autocrine system. We describe the isolation of temperature-sensitive (ts) mutants of MH2 virus. As suggested by marker rescue experiments, one mutant bears a ts lesion in v-mil, whereas the other carries a mutation in v-myc. Ts v-mil MH2-transformed macrophages become factor-dependent at the non-permissive temperature (42 degrees C), while ts-v-myc MH2-transformed macrophages cease growing and acquire a more normal macrophage phenotype at 42 degrees C irrespective of the presence of cMGF. Both phenotypes can be reversed by backshift to the permissive temperature. These results suggest that the gene products of v-mil and v-myc function independently of each other and that v-mil is necessary for the maintenance of autocrine growth, whereas v-myc is required to maintain the transformed phenotype.     

Discrimination of distinct proteinases at the four structural levels of rat liver mitochondria.

Rat liver mitochondrial fractions corresponding to four morphological structures (matrix, inner membrane, intermembrane space and outer membrane) contain proteinases that cleave casein components at different rates. Proteinases of the intermembrane space preferentially cleave kappa-casein, whereas the proteinases of the outer membrane, inner membrane and matrix fractions degrade alpha S1-casein more rapidly. Electrophoretic separation of the degradation products of alpha S1-casein and kappa-casein in polyacrylamide gels shows that different polypeptides are produced when the substrate is degraded by the matrix, by both membranes and by the intermembrane-space fraction. Some of the degradation products resulting from incubation of the caseins with the mitochondrial fractions are probably the result of digestion by contaminating lysosomal proteinase(s). The matrix has a high peptidase activity, since glucagon, a small peptide, is very rapidly degraded by this fraction. These observations strongly suggest that distinct proteinases, with different specificities, are associated respectively with the intermembrane space and with both membrane fractions.     

Primary structure of a structural protein from the cuticle of the migratory locust, Locusta migratoria.

The complete amino acid sequence of a structural protein isolated from pharate cuticle of the locust Locusta migratoria was determined. The protein has an unusual amino acid composition: 42% of the residues are alanine and only 14 of the 20 common amino acid residues are present. The primary structure consists of regions enriched in particular amino acid residues. The N-terminal region and a region close to the C-terminus are enriched in glycine. The rest of the protein is dominated by alanine, except for two short regions enriched in hydrophilic residues. Almost all the proline residues are situated in the alanine-rich regions in a conserved sequence 'A-A-P-A/V'. An internal duplication has taken place covering most of the protein except for the glycine-rich regions. Owing to the unusual features of the protein a combination of automated Edman degradations and plasma-desorption m.s. was used to determine the complete sequence. The protein does not show sequence homology to other proteins, but proteins divided into regions enriched in the same kind of amino acid residues have been isolated from other insect structures.     

Evidence for the involvement of alpha-2 adrenoceptors in the sedation but not REM sleep inhibition by clonidine in the rat

Rats with implanted electrodes for recording of EEG and EMG underwent 12-h recordings during the light period starting after i.p. injections of clonidine (0.1 mg/kg) alone or in combination with different alpha-adrenoceptor antagonists. Clonidine increased the proportion of time the rats spent in the drowsy stage of wakefulness which corresponds to behavioural sedation and inhibited both deep slow wave sleep and REM sleep for 6-9 hours. The amount of active wakefulness or light slow wave sleep were unaffected by clonidine. Yohimbine (1 mg/kg) reversed the increase in drowsy wakefulness by clonidine and increased active wakefulness without affecting sleep. Phentolamine (10 mg/kg) was ineffective against clonidine. Phenoxybenzamine (20 mg/kg) accentuated the sedative effect and prolonged the REM sleep inhibiting effect of clonidine. Prazosin (3 mg/kg) prolonged both the drowsy stage inducing and deep slow wave plus REM sleep inhibiting effects of clonidine. These electrophysiological results support the view that the sedative effect of clonidine in the rat is mediated by alpha-2 adrenoceptors, whereas in this species other mechanisms, possibly another population of alpha-2 receptors, may be involved in the clonidine-induced suppression of deep slow wave sleep and REM sleep.     

Fluid balance in exercise dehydration and rehydration with different glucose-electrolyte drinks

After exercise dehydration (3% of body weight) the restoration of water and electrolyte balance was followed in 6 male subjects. During a 2 h rest period after exercise, a drink of one of four solutions was given as 9 X 300 ml portions at 15 min intervals: control (C-drink), high potassium (K-drink), high sodium (Na-drink) or high sugar (S-drink). An exercise test (submaximal and supramaximal work) was performed before dehydration and after rehydration. Dehydration reduced plasma volume by 16%, a process reversed on resting even before fluid ingestion began, due to release of water accumulated in the muscles during exercise. After 2 h rehydration, plasma volume was above the initial resting value with all 4 drinks. The final plasma volumes after the Na-drink (+14%) and C-drink (+9%) were significantly higher than after the K- and S-drinks. The Na-drink favoured filling of the extracellular compartment, whereas the K- and S-drinks favoured intracellular rehydration. In spite of the higher than normal plasma volume after rehydration, mean heart rate during the submaximal test was 10 bpm higher after rest and rehydration than in the initial test, and was not different between the drinks. The amount of work which could be performed in the supramaximal test (105% VO2max) was 20% less after exercise dehydration and subsequent rest and rehydration than before. This reduction was similar for all drinks, and may be due to a decreased muscle glycogen content (70% of initial) at the time of the second test.     

Swelling of the foot, its vascular volume and systemic hemoconcentration during long-term constrained sitting

Swelling of the left foot and changes in its vascular volume (VV) were studied in seven healthy subjects during 8 h of seated work without leg movements. Changes in total plasma volume (PV) were calculated from hematocrit values. Reference values (r.v.) were obtained during a working day requiring intermittent physical activity (walking). Significant changes during the first 4 h: the foot swelled by 3.5% (r.v.: 2.2%) and VV was reduced by 0.5% of the foot volume (r.v.: increased by 0.3%). Accordingly, the interstitial fluid volume (IFV) of the foot increased by 4.0% (r.v.: 1.9%). The loss of PV was 6.3%. During the last 4 h the only significant change was an increase in foot volume by 1.9%. It is concluded that (1) foot swelling should be corrected for changes in VV to obtain an exact measure of the change in IFV, (2) prolonged elevated pressure, assumed to occur in the feet during relaxed sitting, does not imply distension ("delayed compliance") of the vascular system as previously suggested, (3) hemoconcentration seems to reach complete stability during the initial period of quiet sitting, (4) loss of PV during sedentary work may be avoided by a modest increase in leg activity.