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British Journal of Sports Medicine (1)
Molecular and Cellular Biology (1)
Byng, G S (1)
Jensen, R A (1)
Shapiro, C L (1)
Shapiro, C. M. (1)
Whitaker, R J (1)
Year of Publication
The aromatic amino acid pathway branches at L-arogenate in Euglena gracilis.
Byng, G S
Whitaker, R J
Jensen, R A
Molecular and Cellular Biology
The recently characterized amino acid L-arogenate (Zamir et al., J. Am. Chem. Soc. 102:4499-4504, 1980) may be a precursor of either L-phenylalanine or L-tyrosine in nature. Euglena gracilis is the first example of an organism that uses L-arogenate as the sole precursor of both L-tyrosine and L-phenylalanine, thereby creating a pathway in which L-arogenate rather than prephenate becomes the metabolic branch point. E. gracilis ATCC 12796 was cultured in the light under myxotrophic conditions and harvested in late exponential phase before extract preparation for enzymological assays. Arogenate dehydrogenase was dependent upon nicotinamide adenine dinucleotide phosphate for activity. L-Tyrosine inhibited activity effectively with kinetics that were competitive with respect to L-arogenate and noncompetitive with respect to nicotinamide adenine dinucleotide phosphate. The possible inhibition of arogenate dehydratase by L-phenylalanine has not yet been determined. Beyond the latter uncertainty, the overall regulation of aromatic biosynthesis was studied through the characterization of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase and chorismate mutase. 3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase was subject to noncompetitive inhibition by L-tyrosine with respect to either of the two substrates. Chorismate mutase was feedback inhibited with equal effectiveness by either L-tyrosine or L-phenylalanine. L-Tryptophan activated activity of chorismate mutase, a pH-dependent effect in which increased activation was dramatic above pH 7.8 L-Arogenate did not affect activity of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase or of chorismate mutase. Four species of prephenate aminotransferase activity were separated after ion-exchange chromatography. One aminotransferase exhibited a narrow range of substrate specificity, recognizing only the combination of L-glutamate with prephenate, phenylpyruvate, or 4-hydroxyphenylpyruvate. Possible natural relationships between Euglena spp. and fungi previously considered in the literature are discussed in terms of data currently available to define enzymological variation in the shikimate pathway.
Sleep and the athlete.
British Journal of Sports Medicine
Sleep is generally considered to be restorative and the notion of exercise being associated with the changes in subsequent sleep is popular but has only recently been demonstrated. There are several facets of exercise performed that have an influence on sleep. These include the intensity and duration of the exercise, and the interval between the cessation of exercise and sleep onset. Other factors that may alter sleep after exercise are the age and fitness of the subject, and his lean body mass. Most studies on the effect of exercise on sleep can be interpreted as being partially or totally supportive of the restorative theory of sleep function.
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