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This paper describes the analysis of the evolution of Internet service access for the residential sector with the purpose of obtaining an expression to make predictions about its increase over the next ten years. The models derived from a traditional industrial economy are no longer valid to calculate the evolution of Internet service access. As such, the authors of this paper propose and test a new model to calculate the increase in the percentage of Internet users based on the concepts of a network economy. The new model, combined with the tendency of modem speed evolution, produces a new equation to calculate the bandwidth growth in optical access networks. This way of calculating the bandwidth growth of the access networks is independent of the authors' knowledge of future Internet services. Application of the model to a simulated geographical area is shown. [ABSTRACT FROM PUBLISHER]

Introduction: this paper examines the case of prescription enteral nutritional support tube in Colombia, analyzed from the perspective of the Social Security System in Health, and explained as the result of a problem of institutional coordination. The role and incentives of different actors are identified and shown how the interaction of these discourages the use of enteral nutrition in cases where it is necessary, with corresponding clinical effect for the patient and increased cost for the system., Methods: analysis of the effects it may have in clinical practice the problem of institutional coordination of regulators in the country, analyze their origin and the incentives and interests of the various stakeholders, prior synthesis of the relevant literature review. The search was conducted in the following databases: PubMed, Medline, and Embase ScienceDirect., Conclusions: the current situation of enteral nutritional support in Colombia is the result of a suboptimal equilibrium, resulting from a problem of institutional coordination that can only be solved when the agents to look beyond their local incentives, and nutritional support is a key component of hospital care and constitutes a means to the end: the health of the population served., (Copyright AULA MEDICA EDICIONES 2014. Published by AULA MEDICA. All rights reserved.)

Hydroxyhydroquinone (HHQ) was characterized kinetically as a tyrosinase substrate. A kinetic mechanism is proposed, in which HHQ is considered as a monophenol or as an o-diphenol, depending on the part of the molecule that interacts with the enzyme. The kinetic parameters obtained from an analysis of the measurements of the initial steady state rate of 2-hydroxy p-benzoquinone formation were kcatapp=229.0±7.7 s(-1) and KMapp,HHQ=0.40±0.05 mM. Furthermore, the action of tyrosinase on HHQ led to the enzyme's inactivation through a suicide inactivation mechanism. This suicide inactivation process was characterized kinetically by λmaxapp (the apparent maximum inactivation constant) and r, the number of turnovers made by 1 mol of enzyme before being inactivated. The values of λmaxapp and r were (8.2±0.1)×10(-3) s(-1) and 35,740±2,548, respectively., (© 2014 International Union of Biochemistry and Molecular Biology.)

Objective: Assessing the cost-effectiveness of open or thoracoscopic thymectomy compared to medical therapy in managing myasthenia gravis not associated with thymoma., Methods: A Markov model was designed for evaluating three strategies' cost-effectiveness. Transition probabilities were taken from the pertinent literature; the costs were estimated from official tariff manuals. Incremental cost-effectiveness ratios were estimated and probabilistic and deterministic sensitivity analysis was used for clinical variables, costs and the model's assumptions., Results: Thoracoscopic thymectomy was the most effective and least costly strategy and dominated the other two alternatives. The cost per life year gained was Col $ 1 129 531 without discount and Col $ 805 179 with discount. Univariate sensitivity analysis showed that the main variables affecting the results were the effects' discount rate, the cost of a myasthenic crisis and the probability of complete remission. Thoracoscopy thymectomy was the most cost-effective strategy for different thresholds of willingness to pay in probabilistic analysis., Conclusions: Thoracoscopic thymectomy is a cost-effective strategy in the treatment of MG without thymoma.

The effect of NADH on melanogenesis under aerobic conditions involves three types of reaction: (a) acting as tyrosinase substrate (a competitive substrate of L-tyrosine and L-DOPA), (b) irreversible inactivation acting as a suicide substrate of tyrosinase, and (c) non-enzymatic reduction of o-dopaquinone by NADH. Under anaerobic conditions, NADH irreversibly inhibits the enzymatic forms met-tyrosinase and deoxy-tyrosinase. In this paper, we kinetically characterize this coenzyme as it acts as a tyrosinase suicide substrate and propose a kinetic mechanism to explain its oxidation by tyrosinase. In addition, the compound is characterized as an irreversible inhibitor of met-tyrosinase and deoxy-tyrosinase.

Carbidopa and benserazide have been described as inhibitors of dopa decarboxylase and both have been used in the treatment of Parkinson's disease. Because of their chemical structure as polyphenols, these compounds can behave as substrates of tyrosinase and peroxidase. We demonstrate that these enzymes oxidize both substrates. Since o-quinones are unstable, a chronometric method for enzymatic initial rate determinations was used based on measurements of the lag period in the presence of micromolar concentrations of ascorbic acid to kinetically characterize these substrates. In the case of tyrosinase, the values of the Michaelis constant for both substrates were greater than those described for dopa, although the catalytic constants were lower, probably due to the greater size of the substitute group in carbon 1. As regards peroxidase, the saturation of the enzyme by both substrates is possible, however this effect does not occur with the isomers of dopa. The distance of the charges from the benzene ring may enable the ring to approach the iron of the active site and, therefore, act.

Ellagic acid has been described as an inhibitor of tyrosinase or polyphenol oxidase and, therefore, of melanogenesis. In this work, we demonstrate that ellagic acid is not an inhibitor, but a substrate of mushroom polyphenol oxidase, an enzyme which oxidizes ellagic acid, generating its o-quinone. Because o-quinones are very unstable, we used an oxymetric method to characterize the kinetics of this substrate, based on measurements of the oxygen consumed in the tyrosinase reaction. The catalytic constant is very low at both pH values used in this work (4.5 and 7.0), which means that the Michaelis constant for the oxygen is low. The affinity of the enzyme for the substrate is high (low K(m) (S)), showing the double possibility of binding the substrate. Moreover, a new enzymatic method is applied for determining the antioxidant activity. Ellagic acid shows high antioxidant activity (EC50 = 0.05; number of electrons consumed by molecule of antioxidant = 10), probably because of the greater number of hydroxyl groups in its structure capable of sequestering and neutralizing free radicals.