Dipole moments of random coil polypeptides

The Rotational Isomeric States model is applied to calculate dipole moments of polypeptides of the twenty natural α-amino acids in the random coil state. Dipole moments of each repeat unit (μ_i), are evaluated using a quantum mechanics procedure. Dipole moment ratios ($\text{D}{}_{\mathrm{x}}\text{=}\text{〈μ}{}^2\text{〉}\text{x}\text{μ}{}_{\mathrm{i}}{}^2\text{,}\text{x = number of repeat units}$) of homopolypeptides are calculated and extrapolated to x →?. With a few exceptions, D_? = 0.36 ± 0.1. Ten actual proteins and three enzymes are also studied; their dipole ratios (D_x′ =〈μ〉/x) range from 7.34 to 10.57 in 10^?59 C² m² (6.6–9.5 D²). Diffferences in the values of D_x′ are due mainly to the different contributions, μ_i, of the amino acid residues contained in each polymer, whereas the sequence of amino acids has a very minor effect.     

Insertion of a MalE β-Galactosidase Fusion Protein into the Envelope of Escherichia coli Disrupts Biogenesis of Outer Membrane Proteins and Processing of Inner Membrane Proteins

The synthesis of a membrane-bound MalE β-galactosidase hybrid protein, when induced by growth of Escherichia coli on maltose, leads to inhibition of cell division and eventually a reduced rate of mass increase. In addition, the relative rate of synthesis of outer membrane proteins, but not that of inner membrane proteins, was reduced by about 50%. Kinetic experiments demonstrated that this reduction coincided with the period of maximum synthesis of the hybrid protein (and another maltose-inducible protein, LamB). The accumulation of this abnormal protein in the envelope therefore appeared specifically to inhibit the synthesis, the assembly of outer membrane proteins, or both, indicating that the hybrid protein blocks some export site or causes the sequestration of some limiting factor(s) involved in the export process. Since the MalE protein is normally located in the periplasm, the results also suggest that the synthesis of periplasmic and outer membrane proteins may involve some steps in common. The reduced rate of synthesis of outer membrane proteins was also accompanied by the accumulation in the envelope of at least one outer membrane protein and at least two inner membrane proteins as higher-molecular-weight forms, indicating that processing (removal of the N-terminal signal sequence) was also disrupted by the presence of the hybrid protein. These results may indicate that the assembly of these membrane proteins is blocked at a relatively late step rather than at the level of primary recognition of some site by the signal sequence. In addition, the results suggest that some step common to the biogenesis of quite different kinds of envelope protein is blocked by the presence of the hybrid protein.     

Postnatal Changes in the Activity Ratio of Specific and Nonspecific Cholinesterases from Neuronal Perikarya

Abstract: A soluble fraction from rat brain neuronal perikarya was shown to contain both the specific and nonspecific forms of the enzyme acetylcholines-terase (EC's 3.1.1.7. and 3.1.1.8., respectively). The ratio of the enzyme activities varied along the course of brain development: the nonspecific form being predominant from 1 to 15 days of age and the specific one showing the pattern of rising activity from day 15 onward. We suggest a possible relationship between this changing in cholinesterase activities and the establishment of synapses within the rat cerebral cortex.     

Photosynthetic preparation and characterization of 13C-labeled carbohydrates in agmenellum quadruplicatum

The blue-green alga Agmenellum quadruplicatum (strain PR6) has been used to prepare photobiosynthetically ¹³C-labeled d-glucose, 2-O-(α-d-glucopyranosyl)-glyceric acid (glucosylglycerate), 2-hydroxy-1-(hydroxymethyl)ethyl α-d-gluco-pyranoside (glucosylglycerol), and α-d-glueopyranosyl β-d-fructofuranoside (sucrose). When grown to a cell density of 4.4 g.L^-1 (dry weight) under nitrate-nitrogen limiting growth conditions for 120 h, the algal cells contained 38% of the dry-cell weight as(1 → 4)-α-d-glucan (amylose). About 1% of the dry-cell weight was glucosylglycerol, glucosylglycerate, and sucrose. Glutamate was obtained, together with carbohydrates of low molecular weight, when the cells were extracted with chloroform-methanol; d-glucose was recovered from the extracted cells by acid hydrolysis of the starch. The algae were grown by using 20 mol% [¹³C] carbon dioxide for preparation of labeled carbohydrates and for cellular component identification by whole-cell n.m.r. spectroscopy.     

External mass transfer in a biological film reactor

A method for calculating the mass transfer coefficient in a biological film system, under turbulent flow conditions, is presented. It is experimentally found that fluid velocity has a positive effect on the rate of substrate utilization when the system is operated in other than the kinetic regime. A correlation is developed which indicates a dependence of the mass transfer coefficient on the fluid velocity raised to the 0.7 power.     

Alcohol:NAD oxidoreductase in brain of rats from a colony fed dilute ethanol for many generations.

—Alcohol:NAD oxidoreductase (EC 1.1.1.1) was studied in brain cortex, hypothalamus, cerebellum and midbrain of adult and immature rats, and in the whole encephalon of neonatal rats. The rats used in this study were (i) from a colony which has been given 12% (v/v) aqueous ethanol as the only fluid for 54 generations (‘E.F.’ rats); (ii) rats removed from this colony after the forty-eighth generation and thereafter fed water instead of the alcohol solution (‘E.F./H₂O’ rats); and (iii) normal rats. Enzyme activity in the 20,000 g supernatant of tissue homogenates was measured by the method of Raskin and Sokoloff. Activity was found to be highest in neonatal rat brain and to decrease as the age increased. Activity in the hypothalamus of adult E.F. rats was significantly higher than that found in the same region of adult E.F./H₂O rats. Immature rat cerebellum alcohol:NAD oxidoreductase activity was higher both in ‘E.F.’ and ‘E.F./H₂O’ suggesting a possible genetic change be involved in this CNS region. It may be concluded that, with the exception of neonatal rats, ethanol consumption induces an increase in rat CNS alcohol :NAD oxidoreductase activity.     

Social grooming between squirrel monkeys and uakaris in a seminatural environment

Young squirrel monkeys (Saimiri sciureus) were reported grooming an adult female uakari (Cacajao calvus rubicundus) on four different occasions. Furthermore, the uakari was noted grooming two squirrel monkeys in separate instances. These observations took place in a seminatural rainforest (The Monkey Jungle; Goulds, Florida, U.S.A.) where provisions are provided. Some possible hypostheses tendered to account for this unusual behavior included (a) the unaverted interaction of food-seeking and fur-cleaning behavior, and (b) the compatibility of play-curiosity activities by squirrel monkeys with the uakaris' need for social contact.     

Differential gene expression in whitefly Bemisia tabaci-infested tomato (Solanum lycopersicum) plants at progressing developmental stages of the insect's life cycle

A suppression-subtractive-hybridization (SSH) strategy was used to identify genes whose expression was modified in response to virus-free whitefly Bemisia tabaci ( Bt , biotype A) infestation in tomato ( Solanum lycopersicum ) plants. Thus, forward and reverse SSH gene libraries were generated at four points in the whitefly's life cycle, namely at (1) 2 days (adult feeding and oviposition: phase I); (2) 7 days (mobile crawler stage: phase II); (3) 12 days (second to third instar nymphal transition: phase III) and (4) 18 days (fourth instar nymphal stage: phase IV). The 169 genes with altered expression (up and downregulated) that were identified in the eight generated SSH libraries, together with 75 additional genes that were selected on the basis of their involvement in resistance responses against phytofagous insects and pathogens, were printed on a Nexterion^® Slide MPX 16 to monitor their pattern of expression at the above phases. The results indicated that Bt infestation in tomato led to distinctive phase-specific expression/repression patterns of several genes associated predominantly with photosynthesis, senescence, secondary metabolism and (a)biotic stress. Most of the gene expression modifications were detected in phase III, coinciding with intense larval feeding, whereas fewer changes were detected in phases I and IV. These results complement previously reported gene expression profiles in Bt -infested tomato and Arabidopisis, and support and expand the opinion that Bt infestation leads to the downregulation of specific defense responses in addition to those controlled by jasmonic acid.     

Analysis of the pathways of nitric oxide utilization in mitochondria

The regulatory role that mitochondria play in cell dysfunction and cell-death pathways involves the concept of a complex and multisite regulation of cellular respiration and energy production signaled by cellular and intercellular messengers. Hence, the role of nitric oxide, as a physiological regulator acting directly on the mitochondrial respiratory chain acquires further relevance. This article provides a survey of the major regulatory roles of nitric oxide on mitochondrial functions as an expression of two major metabolic pathways for nitric oxide consumption: a reductive pathway, involving mitochondrial ubiquinol and yielding nitroxyl anion and an oxidative pathway involving superoxide anion and yielding peroxynitrite. The modulation of the decay pathways for nitrogen-and oxygen-centered radicals is further analyzed as a function of the redox transitions of mitochondrial ubiquinol. The interplay among these redox processes and its implications for mitochondrial function is discussed in terms of the mitochondrial steady-state levels (and gradients) of nitric oxide and superoxide anion.     

Magnetic Cross-Linked Enzyme Aggregates (mCLEAs) of Candida antarctica Lipase: An Efficient and Stable Biocatalyst for Biodiesel Synthesis

Enzyme-catalyzed production of biodiesel is the object of extensive research due to the global shortage of fossil fuels and increased environmental concerns. Herein we report the preparation and main characteristics of a novel biocatalyst consisting of Cross-Linked Enzyme Aggregates (CLEAs) of Candida antarctica lipase B (CALB) which are covalently bound to magnetic nanoparticles, and tackle its use for the synthesis of biodiesel from non-edible vegetable and waste frying oils. For this purpose, insolubilized CALB was covalently cross-linked to magnetic nanoparticles of magnetite which the surface was functionalized with –NH₂ groups. The resulting biocatalyst combines the relevant catalytic properties of CLEAs (as great stability and feasibility for their reutilization) and the magnetic character, and thus the final product (mCLEAs) are superparamagnetic particles of a robust catalyst which is more stable than the free enzyme, easily recoverable from the reaction medium and reusable for new catalytic cycles. We have studied the main properties of this biocatalyst and we have assessed its utility to catalyze transesterification reactions to obtain biodiesel from non-edible vegetable oils including unrefined soybean, jatropha and cameline, as well as waste frying oil. Using 1% mCLEAs (w/w of oil) conversions near 80% were routinely obtained at 30°C after 24 h of reaction, this value rising to 92% after 72 h. Moreover, the magnetic biocatalyst can be easily recovered from the reaction mixture and reused for at least ten consecutive cycles of 24 h without apparent loss of activity. The obtained results suggest that mCLEAs prepared from CALB can become a powerful biocatalyst for application at industrial scale with better performance than those currently available.