Studies on evolutionary and selective properties of hypercycles using a Monte Carlo method

Summary The most relevant properties of hypercycles were previously studied mainly from a theoretical point of view. We have developed a Monte Carlo method simulating hypercyclic organization to obtain information about the dynamics of this prebiotic organization. Nucleation, growth, and selective properties have been tested and the results obtained are in good agreement with those of the theoretical predictions. The influence of hypercyclic organization of the error threshold has also been studied. As a consequence of the emergence of a hypercycle, the value of this threshold decreases. The amount of this decrease depends on the population size. Moreover, for some interval of quality factor values, either the hypercycle organization or an error catastrophe can be produced, depending on the initial conditions. The influence of these phenomena on both the dynamic behavior and evolutionary advantages of the hypercycle, as well as their decisive roles on genome size, are discussed.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986     

Energy-dependent formation of free ATP in yeast submitochondrial particles, and its stimulation by oligomycin

Yeast submitochondrial particles, in a P_i- and NADH-dependent reaction, produced low concentrations of free ATP in the absence of added ADP. This formation of free ATP, as measured by the luciferin-luciferase method, was strongly stimulated by oligomycin. For maximal stimulation, oligomycin was to be added not earlier than 5–10 min after the addition of NADH. Upon addition of antimycin or FCCP the system was completely inhibited. The amount of free ATP formed corresponded to one-third of the amount of bound ATP in submitochondrial particles. The stimulatory effect of oligomycin disappeared if the submitochondrial particles were spun down after oligomycin stimulation and then resuspended in the reaction medium, whereas submitochondrial particles with no oligomycin added initially were stimulated by oligomycin after the same procedure. A different picture emerged with addition of ADP. If the submitochondrial particles were preenergized with NADH in the presence of oligomycin before the addition of ADP the formation of free ATP upon subsequent addition of ADP was inhibited by oligomycin. In the presence of oligomycin, but lacking preenergization with NADH, a stimulation of free ATP formation was achieved with added ADP. A possible explanation for the stimulating effect of oligomycin on ATP formation in the absence of added ADP is that it enhances the release of bound ATP in an energy-requiring process. The release of only about one-third of the bound ATP could indicate that one of three nucleotide-binding subunits involved in the mechanism of ATP formation by ATP synthase is in a state suitable for such an energy-dependent release of ATP.     

Tumor promoter chloroform is a potent protein kinase C activator

The major interaction site for tumor-promoting phorbol esters is the calcium-activated, phospholipid-dependent protein kinase (protein kinase C), a key-element in signal transduction. Binding of phorbol esters results in enzyme activation which mediates, at least in part, the action of these agents. We have investigated the effects of tumor promoter chloroform on protein kinase C activity. Like thrombin and 12-O-tetradecanoylphorbol-13-acetate (TPA), chloroform was able to activate protein kinase C in intact rabbit platelets. In addition, chloroform stimulated enzyme activity as well as TPA binding capacity in cell-free system. Scatchard analysis of the data has shown that chloroform increased the number of phorbol ester binding sites. Structurally related compounds, carbon tetrachloride and methylene chloride, activated the enzyme similarly.     

Labeling of lipids of retina subcellular fractions by [1-14C]eicosatetraenoate (20:4(n-6)) docosapentaenoate (22:5(n-3)) and docosahexaenoate (22:6(n-3))

(1-14C)-labeled (n-6) eicosatetraenoate, (n-3) docosapentaenoate and (n-3) docosahexaenoate (20:4, 22:5 and 22:6, respectively) are efficiently taken up and actively esterified into the lipids of bovine retina after 2 h incubation. Photoreceptor membranes, mitochondria, microsomes and postmicrosomal supernatants, which display significant differences in phospholipid and fatty acid compositions, are isolated after such incubations to study the labeling of lipids. The lipid classes preferentially labeled with the acids (1) largely differ among and within subcellular fractions, while (2) some common features in the treatment of the three polyenes are observed in each fraction. In all of them, the three acids are actively incorporated in phosphatidylcholine; ethanolamine glycerophospholipid, phosphatidylserine (PS) and phosphatidylinositol (PI) are highly labeled with 22:6, 22:5 and 20:4 respectively; within ethanolamine glycerophospholipid, the three label phosphatidylethanolamine in preference to plasmenylethanolamine. Most of the 14C esterified in mitochondria is in phospholipids. The endoplasmic reticulum produces in addition highly labeled triacylglycerols, also found in cytosol. High levels of 14C-labeled diacylglycerols are observed exclusively in photoreceptor membranes, where the specific radioactivity of PI is very high. The total amounts of 14C incorporated (1) are in general similar within a given fraction for the three polyenes, but (2) largely differ among fractions. The labeling of the highly unsaturated phospholipids of photoreceptor membranes is the lowest, while the postmicrosomal supernatant (whose lipids are relatively the poorest in polyenoic fatty acids) contains most of the labeled lipids isolated from retinas under these conditions. The results indicate that polyunsaturated species of retina phospholipids undergo an active synthesis and turnover, as well as an intense intracellular traffic among membranes.     

Effect of lectin-binding to fibrinogen D and E domains on coagulation and fibrinolysis

The effect on fibrinogen coagulation and fibrinolysis of the mannose-specific lectins concanavalin A, its acetyl derivative and Lens culinaris agglutinin was studied. Concanavalin A and acetyl-concanavalin A, which bind to the four carbohydrate chains of fibrinogen, and L. culinaris agglutinin, which only binds to the carbohydrate present in fibrinogen D domains, has the same effect on the coagulation rate: an inhibition at low lectin concentrations and an increase at high concentrations. On the other hand, L. culinaris agglutinin does not alter fibrin crosslinking while acetyl-concanavalin A produces a slight inhibition of both gamma-gamma and alpha-polymer formation. However, this effect is very small when compared with the clear inhibitory effect produced by concanavalin A. Concanavalin A and acetyl-concanavalin A have an inhibitory effect on the rate of fibrin clot lysis proportional to the lectin concentration. Nearly 100% inhibition was obtained when two lectin-binding sites were occupied by either concanavalin A or acetyl-concanavalin A. However, L. culinaris agglutinin has a clearly weaker effect and more than 50% inhibition was not observed. The comparative study of the effect of the three lectins on fibrinolysis as well as on the formation of fibrinogen aggregates suggests that the inhibitory effect of concanavalin A and acetyl-concanavalin A is primarily due to their binding to the carbohydrate chains of fibrinogen E domain.     

The cephalic glands of Brazilian reptilia and amphibia. IV. Histology of labial, premaxillary, and Duvernoy's glands in the colubrid snake Oxyrhopus trigeminus

A study of the morphology of the salivary glands of the colubrid snake Oxyrhopus trigeminus showed the following: The acini of supralabial, infralabial, and premaxillary glands are formed by mucous and mucoserous cells; the tubules of Duvernoy's gland are formed by seromucous cells; and mucous cells produce neutral and acid mucosubstances, mucoserous cells secrete neutral and acid mucosubstances and protein, and seromucous cells have neutral mucosubstance and protein secretions.     

Labeling of phosphatidylcholines of retina subcellular fractions by [1-14C]eicosatetraenoate (20:4(n-6)), docosapentaenoate (22:5(n-3)) and docosahexaenoate (22:6(n-3))

The labeling of molecular species of phosphatidylcholine (PC) has been studied in bovine retinas incubated for 2 h with (1-14C)-labeled (n-6) eicosatetraenoate (n-3) docosapentaenoate and (n-3) docosahexaenoate (20:4, 22:5 and 22:6, respectively) and in four subcellular fractions isolated after such incubations. Of the total radioactivity incorporated in PC, the following percentages of the above fatty acids, respectively, are found in its dipolyunsaturated species: 58, 56 and 53% in rod outer segments; 29, 41 and 49% in mitochondria; 24, 28 and 39% in microsomes; 12, 14 and 16% in postmicrosomal supernatants; 28, 36 and 58% in entire retinas. The remainder percentages are in tetra-, penta- and hexaenoic species of PC, respectively. The levels of pentaenoic species in the PCs of all fractions are similar, while tetraenes are lowest and hexaenes highest in photoreceptor membranes. Dipolyunsaturated species are highly concentrated in photoreceptor membranes, but are minor components of mitochondrial, microsomal and cytosolic PC. The specific radioactivities of tetraenoic, pentaenoic and hexaenoic PCs are decreasingly lower in the following order: postmicrosomal supernatants, microsomes, mitochondria, photoreceptor membranes. In contrast, the specific radioactivities of dipolyunsaturated PCs are higher in mitochondria and microsomes than in the other fractions, especially with 22:5 and 22:6. It is suggested that mitochondria as well as the endoplasmic reticulum could play a role in the synthesis and further modifications of dipolyunsaturated PCs before being supplied to photoreceptor membranes.     

A complex balanced chromosomal rearrangement in repeated abortions

Summary A double balanced reciprocal translocation involving four chromosomes, t(1;19;6;14) (1p11; 19p11; 6q25; 14q21), was found in the phenotypically normal husband in a couple referred because of repeated abortions. Reciprocal translocations, t(6;14), had been transmitted by his mother, his father being apparently homozygous for a translocation comprising pairs 1 and 19-t(1;19)(1;19). The genetic consequences of this complex chromosomal rearrangement are analyzed.     

Hydrolysis of rice straw to fermentable sugars byTrichoderma enzymes

Summary ATrichoderma sp. (IMB-Tr) isolated from rice straw possessed cellulolytic and xylanolytic activity, comparable to those produced byTrichoderma reesei QM 9414 (a proven cellulolytic fungus). IMB-Tr produced 2.9 and 1.9 times, respectively, greater -glucosidase activity compared toT. reesei when grown on microcrystalline cellulose and rice straw. Percentage enzymic hydrolysis increased with increase in the sodium hydroxide concentration used in the pretreatment of rice straw and with the increase of enzyme concentration used in the hydrolysis. The extracellular enzyme fraction ofT. reesei possessed greater hydrolytic power than that of IMB-Tr. However, when a combined enzyme preparation from the two organisms was used, an appreciable degree of synergism was observed; an increase in reducing sugars up to 39% was seen. The reducing sugar produced by enzymic hydrolysis was mainly glucose, xylose and cellobiose. Fermentation of a 4.8% (w/v) sugar hydrolysate (produced by the enzymic hydrolysis of rice straw) bySaccharomyces cerevisiae produced 10.7 g/l of ethanol compared to 18.8 g/l produced by the fermentation of 4.8% (w/v) pure glucose.

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Resumen Se ha aíslado a partir de paja de arroz una cepa deTrichoderma sp. (IMB-Tr) que posee actividades celulolíticas y xilanolíticas comparables a las deTrichoderma reesei QM 9414 (un hongo probadamnete celulolítico). IMB-Tr produjo 2.9 y 1.9 veces más actividad -glucosidásica queT. reesei cuando ambos se hicieron crecer en celulosa microcristalina y en paja de arroz respectivamente. El porcentaje de hidrolisis enzimática se incrementó con el aumento en la concentración del hidróxido sódico empleado en el pretratamiento de la paja de arroz y con el aumento de la concentración enzimática utilizada en la hidrolisis. La fracción extracelular enzimática deT. reesei poseía un mayor poder hidrolítico que la de IMB-Tr, sin embargo cuando se usó un preparado enzimático combinado de ambos microorganismos se obtuvo un apreciable efecto sinérgico, observándose un incremento de hasta un 39% de los azucares reductores producidos. Estos azucares fueron principalmente glucosa, xilosa y celobiosa. La fermentación de un 4.8% (p/v) del hidrolisado azucarado (producido por la hidrolisis enzimática de la paja de arroz) porSaccharomyces cerevisiae produjo 10.7 g/l de etanol comparado a 18.8 g/l obtenidos de la fermentación de 4.8% (p/v) de glucosa pura.

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Résumé Une souche deTrichoderma sp. (IMB-Tr), isolée à partir de paille de riz, a une activité cellulolytique et xylanolytique comparable à celle deTrichoderma reesei QM 9414 (champignon cellulolytique reconnu). L'activité -glucosidase d'IMB-Tr cultivé sur cellulose micro-cristalline ou sur paille de riz est, respectivement, 2.9 et 1.9 fois plus élevée que celle deT. reesei. Le pourcentage d'hydrolyse enzymatique croit avec la concentration de la soude employée pour le pré-traitement de la paille et avec la concentration d'enzyme utilisée pour l'hydrolyse. La fraction exocellulaire de l'enzyme a une activité hydrolysante plus élevée dans le cas deT. reesei que dans celui de IMB-Tr. Cependant, si on emploie un mélange des activités enzymatiques des deux organismes, on constate une nette synergie et un accroissement des sucres réducteurs allant jusqu'à 39%. Les sucres réducteurs obtenus par hydrolyse enzymatique comprennent principalement du glucose, du xylose et du cellobiose. La fermentation parSaccharomyces cerevisiae d'un hydrolysat enzymatique de paille de riz contenant 4.8% (poids/vol.) de sucres fournit 10.7 g/l d'éthanol, au lieu de 18.8 g/l obtenus par fermentation de glucose pur à la même concentration.