Is the cytoskeleton-plasma membrane complex involved in lens protein biosynthesis?

Calf lens fiber cells contain a population of polyribosomes that direct, at leastin vitro, the synthesis of a specific plasma membrane protein MP26. This protein may serve as a marker in terminal differentiation, since it is absent in the lens epithelium but appears in lens fiber plasma membranes. The MP26 manufacturing polyribosomes are found to be associated with a structural complex in which also the cytoskeleton and plasma membranes participate. They can be released from the complex by treatment with DNAse I. This result presumably reflects the involvement of actin in the linkage of the MP26 synthesizing polyribosomes to the cytoskeleton-membrane complex.     

Is peroxidase involved in ethylene biosynthesis?

Wheat (Triticum aestivum L. cv. Jubilar) coleoptile segments convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. This process is totally inhibited by nitrogen atmosphere and severely inhibited by free radical scavengers (sodium benzoate, ferulic acid), inhibitors of reactive -SH groups ( p -chlormercuribenzoate, iodoacetate), CoCl₂ and EDTA. Indole-3-acetic acid, aminoethoxyvinyl glycine, cycloheximide, actinomycin D, pyridoxal phosphate and NADH have no effect on ACC conversion to ethylene. Some in vivo characteristics of this conversion suggest that it could be catalyzed by peroxidase. However, isoperoxidase B1 isolated from wheat seedlings was not able to catalyze in vitro conversion of ACC to ethylene under a wide range of reaction conditions. Therefore, it is concluded that peroxidase is not directly involved in ethylene biosynthesis.     

Is the membrane attack complex of complement an enzyme?

Summary Recent studies on the functional activities of the membrane attack complex of complement, C5b-9, are reviewed. A new speculative hypothesis has been advanced to account for the ability of complement to mediate lysis of various targets. This hypothesis has three major elements: 1) that the membrane attack complex is an enzyme; 2) that the substrate for this putative enzyme is a membrane constituent; 3) that the substrate specificity of the putative enzyme is dependent on the species source of individual complement components within the C5b-9 complex.Abbreviations E = sheep red cells - A = rabbit IgM anti-Forssman antibody - Hu or hu = human - GP or gp = guinea pig     

Characterization and analysis of the regulatory network involved in control of lipomycin biosynthesis in Streptomyces aureofaciens Tü117

Analysis of the α-lipomycin biosynthesis gene cluster of Streptomyces aureofaciens Tü117 led to the identification of five putative regulatory genes, which are congregated into a subcluster. Analysis of the lipReg1–4 and lipX1 showed that they encode components of two-component signal transduction systems (LipReg1 and LipReg2), multiple antibiotics resistance-type regulator (LipReg3), large ATP-binding regulators of the LuxR family-type regulator (LipReg4), and small ribonuclease (LipRegX1), respectively. A combination of targeted gene disruptions, complementation experiments, lipomycin production studies, and gene expression analysis via RT-PCR suggests that all regulatory lip genes are involved in α-lipomycin production. On the basis of the obtained data, we propose that LipReg2 controls the activity of LipReg1, which in its turn govern the expression of the α-lipomycin pathway-specific regulatory gene lipReg4. The ribonuclease gene lipX1 and the transporter regulator lipReg3 appear to work independently of genes lipReg1, lipReg2, and lipReg4.     

α-Glucosidase from a strain of deep-sea Geobacillus: a potential enzyme for the biosynthesis of complex carbohydrates

An α-glucosidase from Geobacillus sp. strain HTA-462, one of the deepest sea bacteria isolated from the sediment of the Mariana Trench, was purified to homogeneity and estimated to be a 65-kDa protein by SDS-PAGE. At low ion strength, the enzyme exists in the homodimeric form (130 kDa). It is a thermo- and alkaline-stable enzyme with a half-life of 13.4 h and a maximum hydrolytic activity at 60°C and pH 9.0 in 15 mM glycine–NaOH buffer. The enzyme exclusively hydrolyzed α-1,4-glycosidic linkages of oligosaccharides in an exo-type manner. The enzyme had an overwhelming transglycosylation activity and glycosylated various non-sugar molecules when maltose was used as a sugar donor. It converted maltose to isomaltose. The gene encoding the enzyme was cloned and sequenced. The recombinant enzyme could be extracellularly overproduced by Bacillus subtilis harboring its gene and preserved the primary properties of the native enzyme. Site-directed mutagenesis experiments showed that Asp98 is essential for the enzyme activity in addition to Asp199, Asp326, and Glu256.     

Is the enzyme a powerful reactant of the biochemical reaction?

The mainstream explanation of enzyme catalysis relies on the assumption that enzymes can utilize the binding energy. The author suggest that (i) an enzyme with excess free energy first gives a group from its active site into the final place of the bound reactant (substrate) in order to break the first initial chemical bond; (ii) this enzyme accepts a similar group from the second bound reactant (or second group in the case of the single-substrate) into active site and finish the substrate conversion and enzyme regeneration. The detailed mechanisms of the well-studied reactions of peptide bond hydrolysis catalyzed by α-chymotrypsin and the glyceraldehyde-3-phosphate interconversion steps in glycolysis are in accordance with the proposed theoretical conclusions.     

Is neurotensin in the brain involved in thermoregulation of the monkey?

Cannulae for intracerebroventricular (ICV) infusion were implanted stereotaxically in monkeys (Macaca fasicularis) maintained post-operatively in a primate restraint chair. During each experiment, a series of physiological measures was recorded simultaneously on a polygraph which included colonic temperature, vasomotor tone, heart rate, respiratory rate, and basal metabolism as reflected by O₂ uptake. The ICV infusion in a volume of 0.5 ml of neurotensin (NT) in doses ranging from 3–150 μg produced neither a statistically significant nor consistent change in body temperature or vasomotor response. Although the highest dose of 450 μg NT infused ICV caused an immediate bradycardia and a concomitant decline in metabolic and respiratory rates, an average decline in core temperature of 0.6°C and the accompanying cutaneous vasodilation often had a latency as long as 1.0 hr. In contrast to the typical hypothermia in this species following an ICV infusion of catecholamines, implicated in the central pathways underlying thermoregulation, NT failed to elicit a coordinated set of physiological responses for heat dissipation in the monkey. Therefore, it is unlikely that this tridecapeptide plays a role in the central mechanisms mediating the control of body temperature of this primate species.     

Are there errors in glycogen biosynthesis and is laforin a repair enzyme?

Glycogen, a branched polymer of glucose, is well known as a cellular reserve of metabolic energy and/or biosynthetic precursors. Besides glucose, however, glycogen contains small amounts of covalent phosphate, present as C2 and C3 phosphomonoesters. Current evidence suggests that the phosphate is introduced by the biosynthetic enzyme glycogen synthase as a rare alternative to its normal catalytic addition of glucose units. The phosphate can be removed by the laforin phosphatase, whose mutation causes a fatal myoclonus epilepsy called Lafora disease. The hypothesis is that glycogen phosphorylation can be considered a catalytic error and laforin a repair enzyme.     

Is somatostatin or a somatostatin-like peptide involved in central nervous system control of gastric secretion?

Intracisternal injection of octapeptide analogs of somatostatin (SS), Cys-Phe-Phe-D-Trp-Lys-Thr-Phe-Cys (des-AA1,2,4,5,12,13-[D-Trp8]SS (ODT8-SS)) and Cys-Phe-Phe-D-Trp-Lys-Thr-Phe-D-Cys, increased the volume and the acid output of gastric secretion in rats. ODT8-SS given intravenously did not affect basal gastric secretion. The gastrosecretory effect of ODT8-SS, administered intracisternally is dose-dependent (0.01-1 micrograms), long acting, reversible, specific, and abolished by vagotomy, or systemic injection of atropine or SS. SS (5-10 micrograms) or [D-Trp8]SS (1 microgram) had no effect on gastric secretion when given intracisternally. These results demonstrate that some octapeptide SS analogs, unlike SS or other SS analogs, have the capability to act in the brain to induce a vagal dependent stimulation of gastric secretion.     

Is there a circadian rhythm of postural control and perception of the vertical?

Daytime activity is largely regulated by the day/night pattern. Various physiological and cognitive functions display a variation during the diurnal period, where individuals manage their balance, spatial orientation and consequently their perception of the vertical. However, findings concerning daytime changes of postural control quality remain contradictory, mainly due to methodogical considerations. The aim of our study is to evaluate the effect of time of day on postural control and perception of the vertical.

Fifteen male subjects underwent six test sessions over a 24-hour period. Each session involved a postural balance test (static/dynamic; eyes open/closed) and a subjective evaluation of sleepiness, fatigue and subjective visual vertical (SVV) (light stick tilted from 10 to 40°; eight trials). No time-of-day effect was observed on postural balance. However, perception of the vertical fluctuates during the day and is better at 10 a.m. than at 10 p.m. Despite the gradual perception of the vertical deterioration over the day, postural balance does not show any fluctuation. This postural balance consistency throughout the day may be the result of compensation mechanisms.     

Plasmid- and chromosome-encoded redundant and specific functions are involved in biosynthesis of the siderophore anguibactin in Vibrio anguillarum 775: a case of chance and necessity?

We report the identification of a novel chromosome cluster of genes in Vibrio anguillarum 775 that includes redundant functional homologues of the pJM1 plasmid-harbored genes angE and angC that are involved in anguibactin biosynthesis. We also identified in this cluster a chromosomal angA gene that is essential in anguibactin biosynthesis.     

Multiple functions of insulin-degrading enzyme: a metabolic crosslight?

Insulin-degrading enzyme (IDE) is a ubiquitous zinc peptidase of the inverzincin family, which has been initially discovered as the enzyme responsible for insulin catabolism; therefore, its involvement in the onset of diabetes has been largely investigated. However, further studies on IDE unraveled its ability to degrade several other polypeptides, such as β-amyloid, amylin, and glucagon, envisaging the possible implication of IDE dys-regulation in the “aggregopathies” and, in particular, in neurodegenerative diseases. Over the last decade, a novel scenario on IDE biology has emerged, pointing out a multi-functional role of this enzyme in several basic cellular processes. In particular, latest advances indicate that IDE behaves as a heat shock protein and modulates the ubiquitin–proteasome system, suggesting a major implication in proteins turnover and cell homeostasis. In addition, recent observations have highlighted that the regulation of glucose metabolism by IDE is not merely based on its largely proposed role in the degradation of insulin in vivo. There is increasing evidence that improper IDE function, regulation, or trafficking might contribute to the etiology of metabolic diseases. In addition, the enzymatic activity of IDE is affected by metals levels, thus suggesting a role also in the metal homeostasis (metallostasis), which is thought to be tightly linked to the malfunction of the “quality control” machinery of the cell. Focusing on the physiological role of IDE, we will address a comprehensive vision of the very complex scenario in which IDE takes part, outlining its crucial role in interconnecting several relevant cellular processes.     

Is a ferroxidase involved in the high-affinity iron uptake in Chlamydomonas reinhardtii?

In phosphorus deficient soils and under smallscale farming systems, the development of efficient management strategies for P fertilizers is crucial to sustain food production. A field experiment was conducted on a P-fixing Acrisol in western Kenya to study possibilities of replenishing soil P with seasonal additions of small rates of P fertilizers. Triple superphosphate was applied at 0, 10, 25, 50 and 150 kg P ha^–1 for 5 consecutive maize growing seasons followed by 4 seasons of residual crops. Maize yields and soil P fractions were determined. Although maize responded to additions of 10 kg P ha^–1 with a cumulative grain yield of 16.8 Mg ha^–1, at the end of the experiment, compared to 8.8 Mg ha^–1 in the non-P fertilized plots, soil labile P did not increase correspondingly. Seasonal additions of 150 kg P ha^–1 increased maize yields to a cumulative value of 39 Mg ha^–1 at the end of the experiment, and increased all soil inorganic P fractions. At the third season of residual phase, treatment with a cumulative addition of 750 kg P ha^–1 gave the highest yields compared to treatments in the same residual stage, but these yields were considered less than the maximum yield of the season. This indicates that the large build up of soil P was not available for crop uptake. The inorganic P fraction extracted by NaHCO₃ was the most affected by changes in management, increasing during the input phase and decreasing after interruption of P addition, for all P rates. The decrease in this pool during the residual phase could be explained by the maize uptake. This study showed that seasonal additions of 25 kg P ha^–1 can increase maize yield with gradual replenishment of soil P.     

Inheritance of the replication complex: a unique or common phenomenon in the control of DNA replication?

Early models of the regulation of initiation of DNA replication by protein complexes predicted that binding of a replication initiator protein to a replicator region is required for initiation of each DNA replication round, since after the initiation event the replication initiator should dissociate from DNA. It was, therefore, assumed that binding of the replication initiator is a signal for triggering DNA replication. However, more recent investigations have revealed that in many replicons this is not the case. Studies on the regulation of the replication of plasmids derived from bacteriophage lambda demonstrated that, once assembled, the replication complex can be inherited by one of the two daughter plasmid copies after each replication round and may function in subsequent replication rounds. Since this DNA-bound protein complex bears information about specific initiation of DNA replication, this phenomenon has been called "protein inheritance." A similar phenomenon has recently been reported for oriJ-based plasmids. Moreover, the current model of the initiation of DNA replication in the yeast Saccharomyces cerevisiae proposes that the origin recognition complex (ORC) remains bound to one copy of the ori sequence (the ARS region) after initiation of DNA replication. Thus, it seems plausible that protein inheritance is not unique for lambda plasmids, but may be a common phenomenon in the control of DNA replication, at least in microbes.     

Is cyclic AMP involved in the defibrillating effect of sotalol ?

Ventricular fibrillation induced in animals pretreated with sotalol, a class III antiarrhythmic agent, would spontaneously terminate and revert into a sinus rhythm. This phenomenon has been atributed to the class III action of this Drug, I.e., prolongation of myocardial action potential duration and effective refractory period. Since various observations suggested that these alone cannot explain the defibrillating phenomenon, we hypothesised that sotalol affeced ventricular intercellular synchronization by increasing intercellular coupling. Our recent experimental studies have shown that sotalol antagonized the cellular decoupling to guinea pig ventricular muscle strip caused by perfusion with either a hypoxic normal Tyrode's solution or an oxygenated high Ca2+ Tyrode's solution. We assumed that the most likely mechanism for the restoration of intercellular coupling would be by increasing intracellular cAMP concentration. In order to test this hypothesis, we studied the modification of this sotalol-induced recoupling by a cAMP dependent protein kinase inhibitor. The results clearly supported our assumption since the addition of Arg-Gly-Tyr-Ala-Leu-Gly (pure A- kinase inhibitor) prevented the aforementioned cellular recoupling action of sotalol in a dose-dependent manner. It can thus be concluded that changes in intracellular cAMP level are involved in the synchronizing /defibrillating effect of sotalol.     

Is cholinergic activity of the caudate nucleus involved in memory?

A review was made of experiments dealing with the involvement of cholinergic activity of the caudate nucleus in memory processes. Injections of acetylcholine-receptor blockers or of neurotoxins against cholinergic interneurons into the striatum produce marked impairments in acquisition and retention of instrumental tasks while injections of acetylcholine or choline into the caudate produce the opposite effect. However, after a period of overtraining cholinergic blockade or interference with neural activity of the caudate does not produce significant deficits in retention. It is concluded that striatal cholinergic activity is critically involved in memory of recent events and that long-term memory is mediated by different neurochemical systems outside the caudate nucleus.     

Are differences in FSH concentrations involved in the control of ovulation rate in Romanov and Ile-de-France ewes?

Despite differences in FSH concentrations ranging from 1.5 ng/ml (Romanov ewes) to 4 ng/ml (Ile-de-France ewes) between the follicular and luteal phases, follicular growth (numbers of follicles growing, growth rates, maximum size reached) was morphologically similar between the two stages of the cycle. Injection of 750 i.u. hCG at Day 6 or 16 of the cycle triggered ovulation of 4.1 +/- 0.7 and 4.0 +/- 1.3 follicles in Romanov and 2.2 +/- 0.5 and 1.7 +/- 0.5 follicles in Ile-de-France ewes, respectively, demonstrating that functional differentiation was similar between the two stages of the cycle. As gonadotrophin environment differs between these two stages of the cycle, this suggests that there is a wide flexibility in the amount of gonadotrophins required to trigger terminal follicular growth and that ovarian requirements for gonadotrophins might work through thresholds. When Romanov and Ile-de-France ewes were given similar amounts of exogenous gonadotrophins (1250 i.u. PMSG, 750 i.u. hCG) after hypophysectomy, ovulation rates were close to the usual values (Romanov, 5.5 +/- 3.9; Ile-de-France, 1.4 +/- 0.5), demonstrating that differences in gonadotrophin concentrations during the follicular phase do not play a major role in the high ovulation of the Romanov compared to the Ile-de-France ewes.