Starch-based extruded plastic films and evaluation of their biodegradable properties

Plastic formulations containing up to 40% starch were prepared and blown into thin films using extrusion methods. Extruded films were evaluated for their biodegradability by exposing them to a consortium of starch degrading bacteria in the laboratory for 45 days and in the ‘La Silla’ river located in Monterrey, N.L. Mexico for up to 60 days. Biodegradability was assessed by measuring changes in weight loss and chemical composition of the films using Fourier transform infrared (FTIR) spectroscopy. While little or no degradation was apparent in control films made up of 100% low density polyethylene (LDPE) or 100% poly-(ethylene-co-acrylic acid) (EAA), most of the starch was depleted in starch-containing films exposed in the river. Starch degradation in films exposed to amylolytic bacteria in the laboratory was relatively slower. Also, increasing the amount of EAA from 25% to 50% substantially reduced starch depletion in these films.     

Two-dimensional proton magnetic resonance of human muscle extracts

In continuation of our previous work on one-dimensional (1D) proton nuclear magnetic resonance (1H-NMR) of normal and diseased human muscle extracts we recorded the two-dimensional (2D) J-correlated proton magnetic resonance spectra of these extracts. Significant differences between normal and diseased muscle extracts, not observed in the 1D 1H-NMR spectra, were seen from their 2D connectivity contour patterns. Taurine was not present in cerebral palsy muscle extract while both normal and scoliosis muscles contained this metabolite. Only the normal muscle had carnitine. Carnosine was present in all muscles. alpha-Ketoglutarate was found only in the diseased muscle extracts. While the amino acids lysine, cysteine and glutamine were common to normal and diseased muscles, threonine was seen only in the diseased muscles. Additional small differences were detected in the 2D patterns of human muscle extracts.     

Role of the presynaptic receptors in the control of dopamine synthesis in the striate complex and nucleus accumbens

The role of presynaptic receptors on dopamine synthesis, at both nigrostriatal and mesolimbic systems, has been studied after dopamine uptake drastically increases the dopamine and DOPAC levels at n. accumbens but not at striatum. The present data suggest that presynaptic receptors are a decisive factor regulating dopamine synthesis at nigrostriatal system. However, the end-product inhibition could be the most important autoregulatory mechanism at the mesolimbic system.     

Synthesis,RNAi activity and nuclease-resistant properties of apolar carbohydrates siRNA conjugates

Oligoribonucleotide conjugates carrying apolar carbohydrates at the 5′-end and the corresponding siRNA duplexes have been prepared using phosphoramidite chemistry. All the carbohydrate-siRNA derivatives were compatible with RNA interference machinery if transfected with oligofectamine. In the absence of a transfection agent, some of them exerted certain reduction of gene expression. Double-tailed permethylated glucose conjugated to siRNA through a long spacer inhibited gene expression up to 26% compared to the scrambled duplex. Such modifications contribute positively to the stability of oligoribonucleotides against 5′-exonuclease degradation.     

Photomechanical migrations of pigment granules along the retinula cells of the crayfish

The light-dependent migrations of proximal pigment granules along the photoreceptors of the crayfish compound-eye were studied in isolated retinas and eyestalks. The extent and kinetics of movement in each direction were found quantitatively equivalent to those observed in the organ in situ. These and other features make these cells to appear as intrinsically independent pigmentary effectors, directly responsive to light. During dark adaptation (DA) the pigment migrates away from the cell nucleus and accumulates along the axon in two distinct steps. Each step constitutes half of the total distance of about 180 microns and proceeds at 0.30 micron/sec. Only prolonged metabolic impairment inhibited the first phase, while the second was blocked by hypoxia, cyanide, colchicine, and D2O. The maintenance of a full DA position was also shown to be highly dependent upon metabolism. Light incidence on DA eyes is followed by an apparently monophasic expansion of the pigment from the axon towards the perikaryl region at 0.38 micron/sec. This movement was not affected by any of the foregoing agents and seems to be a passive relaxation process. Cytochalasin B had no effect on either motion. The migration in either direction has an exponential time course and is temperature dependent. Electron microscopy revealed two separate patterns of cytoplasmic organization corresponding to the cell areas where the two phases of DA occur. In the region close to the nucleus the pigment appears irregularly scattered, whereas in the axon the granules are situated arond a thick longitudinal bundle of microtubules. These results suggest the existence of two different mechanisms of pigment granule translocation operating in two separate regions of the retinula cell.