142 research outputs found

    Mammalian tyrosinase: Effect of ions on enzyme action

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    1. 1. The univalent cations Li+, Na+, K+, and NH4+ have no effect on tyrosinase action.2. 2. The anions, fluoride, chloride, acetate, and oxalate, consistently inhibit the tyrosine-tyrosinase and dopa-tyrosinase reactions. Iodate, persulfate, and nitrite also inhibit these reactions. Relatively large amounts of these anions are required to produce inhibition.3. 3. Of 24 metal ions tested, only mercury, silver, and gold can produce an inactive enzyme preparation. The ions compete with copper ions for active centers on apotyrosinase. These competitive inhibition reactions are only slowly reversible.4. 4. No cations or anions accelerate tyrosinase action.5. 5. Copper ions are not bound to tyrosinase by a mercaptide linkage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32541/1/0000652.pd

    Entry into New Niches: The Effects of Firm Age and the Expansion of Technological Capabilities on Innovative Output and Impact

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    We provide evidence that young firms systematically differ from older firms in their innovative output when they enter 'new to the firm' technological niches. We analyze data from 128 biotechnology firms since their inception and track these firms over time. Our analyses reveal that the organizational age at which the firm branches into new technological niches significantly influences its innovative activity. We refine the focus of the extant literature by separately examining the effects of branching on the quantity of innovative output and the impact that this output has on the technology domain. Subsequent to branching into new niches, we find that older firms have a higher quantity of output than their younger counterparts, whereas young firms tend to outpace their older rivals with higher impact. We discuss the implications of these findings for the literature on dynamic capabilities and entrepreneurship. © 2011 John Wiley & Sons, Ltd.link_to_subscribed_fulltex

    Politics ahead of patients: The battle between medical and chiropractic professional associations over the inclusion of chiropractic in the American Medicare System

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    Health care professions struggling for legitimacy, recognition, and market share can become disoriented to their priorities. Health care practitioners are expected to put the interests of patients first. Professional associations represent the interests of their members. So when a professional association is composed of health care practitioners, its interests may differ from those of patients, creating a conflict for members. In addition, sometimes practitioners’ perspectives may be altered by indoctrination in a belief system, or misinformation, so that a practitioner could be confused about the reality of patient needs. Politicians, in attempting to find an expedient compromise, can value a “win” in the legislative arena over the effects of that legislation. These forces all figure into the events that led to the acceptance of chiropractic into the American Medicare system. Two health care systems in a political fight lost sight of their main purpose: to provide care to patients without doing harm. Dans leur recherche de lĂ©gitimitĂ©, de reconnaissance et d’une juste part sur le marchĂ© de la santĂ©, les professionnels de la santĂ© peuvent perdre de vue leurs prioritĂ©s. Ces praticiens doivent donner prĂ©sĂ©ance aux intĂ©rĂȘts des patients tandis que les associations professionnelles reprĂ©sentent ceux de leurs membres. Lorsqu’une association professionnelle regroupe des praticiens de la santĂ© cependant, ses intĂ©rĂȘts s’opposent parfois Ă  ceux des patients, crĂ©ant ainsi un conflit pour les membres. De plus, les praticiens peuvent ĂȘtre endoctrinĂ©s par un systĂšme de valeurs ou mal informĂ©s, au point de se tromper dans l’évaluation des besoins rĂ©els des patients. De leur cĂŽtĂ©, les politiciens peuvent prĂ©fĂ©rer une « victoire » dans l’arĂšne lĂ©gislative Ă  une juste apprĂ©ciation des impacts d’une loi. Ces forces ont toutes participĂ© aux Ă©vĂšnements qui ont menĂ© Ă  l’acceptation de la chiropraxie par le systĂšme amĂ©ricain Medicare. Dans cette bataille politique, deux systĂšmes de santĂ© ont nĂ©gligĂ© leur principal objectif : soigner des patients sans leur nuire
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