Comparison of the expression of cell surface poly-N-acetyllactosamine-type oligosaccharides in PC12 cells with those in its variant PC12D.

To explore the biological role of carbohydrate chains in the process of nerve cell differentiation, we carried out a characterization of the carbohydrate structure of glycoproteins by comparing conventional PC12 cells with variant cells (PC12D). In vitro metabolic labeling of cells with either [(3)H] glucosamine or [(3)H] threonine, together with tomato lectin staining, revealed that nerve growth factor (NGF) stimulation caused a decrease in the poly-N-acetyllactosamine synthesis of high-molecular-weight glycopeptides from PC12 cells. By comparison, the amount of glycopeptides with poly-N-acetyllactosamine from PC12D cells was already significantly low and it was not changed by NGF stimulation. By assaying the glycosyltransferases that participate in poly-N-acetyllactosamine synthesis, the decrease in the amount of the poly-N-acetyllactosamine in PC12D cells as well as NGF-stimulated PC12 cells could be accounted for by a reduction in the activity of poly-N-acetyllactosamine extension enzyme (GnT-i), because the amount of poly-N-acetyllactosamine in both cells precisely correlated with changes in GnT-i activity, whereas the activities of N-acetylglucosaminyltransferase V (GnT-V) and beta 1-4 galactosyltransferase remained unchanged. These results demonstrate that the decrease in poly-N-acetyllactosamine synthesis in PC12 cells occurred prior to neurite formation, whereas PC12D cells were insensitive to this effect. Next, we showed that GnT-i but not GnT-V catalyzed a rate-limiting reaction in the expression of poly-N-acetyllactosamine chains, especially in pheochromocytoma.     

A comparison of ferric-chelate reductase and chlorophyll and growth ratios as indices of selection of quince,pear and olive genotypes under iron deficiency stress

Quince (Cydonia oblonga Mill.), pear (Pyrus communis L.) and olive (Olea europaea L.) genotypes were evaluated for their tolerance to iron deficiency stress by growing young plants in three types of aerated nutrient solutions: (1) with iron, (2) without iron or (3) low in iron and with 10 mM bicarbonate. Plants were obtained either from rooted softwood cuttings or from germination of seeds. The degree of tolerance was evaluated with several indices: (1) the chlorophyll content, (2) the root Fe³⁺ reducing capacity and (3) the whole plant relative growth. Fifteen hours before Fe³⁺ reducing capacity determination, iron was applied to the roots of plants with iron-stress, since this method resulted in increasing the reductase activity. All quince and pear genotypes increased the root Fe³⁺ reducing capacity when grown in the treatments for iron-stress, in relation to control plants of the same genotypes. In olive cultivars, the Fe³⁺ reducing capacity was lower in the iron-stress treatments than in the control one. Studying the relationship between relative growth and chlorophyll content for each genotype under iron-stress, in relation to both indices in control plants, a classification of species and genotypes was established. According to that, most olive cultivars and some pear rootstocks and cultivars appear more iron-efficient than quince rootstocks. Our study shows that in some woody species, determining root Fe³⁺ reducing capacity is not the best method to establish tolerance to iron deficiency stress.     

Disruption of axonal transport and neuronal viability by amyloid precursor protein mutations in Drosophila.

We tested the hypothesis that amyloid precursor protein (APP) and its relatives function as vesicular receptor proteins for kinesin-I. Deletion of the Drosophila APP-like gene (Appl) or overexpression of human APP695 or APPL constructs caused axonal transport phenotypes similar to kinesin and dynein mutants. Genetic reduction of kinesin-I expression enhanced while genetic reduction of dynein expression suppressed these phenotypes. Deletion of the C terminus of APP695 or APPL, including the kinesin binding region, disrupted axonal transport of APP695 and APPL and abolished the organelle accumulation phenotype. Neuronal apoptosis was induced only by overexpression of constructs containing both the C-terminal and Abeta regions of APP695. We discuss the possibility that axonal transport disruption may play a role in the neurodegenerative pathology of Alzheimer's disease.     

Cadmium-substituted skeletal troponin C metal binding investigations and sequence assignment of the cadmium-113 resonances

The binding of cadmium to the calcium binding subunit of skeletal troponin (STnC) has been reinvestigated using direct binding methods and fluorescent derivatives. These data provide straightforward explanations of the observed titration behavior in the 113Cd NMR (Ellis, P.D., Strang, P., and Potter, J.D. (1984) J. Biol. Chem. 259, 10348-10356). Further, fluorescent derivatives of skeletal troponin C provide an excellent means of establishing a sequence assignment for the resonances observed in the 113Cd NMR. The results of these experiments demonstrate that sites I and II, the Ca2+ regulatory sites, can be assigned to resonances at -108.5 and -101.5 ppm, respectively. Sites III and IV, the structural sites, are assigned to resonances -112.8 and -106.8 ppm, respectively. These data are discussed in terms of recent structural findings and speculations.     

Effect of training on the rating of perceived exertion at the ventilatory threshold

The purpose of this study was to determine the effect of training on the rating of perceived exertion (RPE) at the ventilatory threshold. College students were assigned to either training (n = 17) or control (n = 10) groups. Trainers completed 18 interval training sessions (five X 5 min cycling at 90-100% VO2max) and 8 continuous training sessions (40 min running or cycling) in 6 weeks. Pre- and post-training, cardiorespiratory, metabolic, and perceptual variables were measured at the ventilatory threshold during graded exercise tests on a cycle ergometer. Ventilatory threshold was that point above which VE X VO2-1 increased abruptly relative to work rate. Post-training means of trained and control subjects were compared using analysis of covariance, with pre-training values as covariates. Following training, the adjusted means for the trained subjects were significantly greater (p less than 0.05) than for controls for VO2max (6%), and for work rate (20%), VO2 (23%), and %VO2max (13%) at the ventilatory threshold. However, adjusted means for RPE at the ventilatory threshold were not significantly different (2%). Both before and after training, exercise at the ventilatory threshold was perceived as 'somewhat hard' to 'hard' (RPE = 13-15) by both groups. The relationship between RPE and %VO2max was altered by training, with trained subjects having a lower RPE at a given %VO2max. It is concluded that RPE at the ventilatory threshold is not affected by training, despite that after training the ventilatory threshold occurs at a higher work rate and is associated with higher absolute and relative metabolic and cardiorespiratory demands.