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Dynamic Medicine

, 5:3

First Online: 24 January 2006Received: 23 June 2005Accepted: 24 January 2006


BackgroundMyoglobin Mb is the simplest monomeric hemoprotein and its physicochemical properties including reversible oxygen O2binding in aqueous solution are well known. Unexpectedly, however, its physiological role in intact muscle has not yet been established in spite of the fact that the role of the more complex tetrameric hemoprotein, hemoglobin Hb, in red cells is well established. Here, I report my new findings on an overlooked property of skeletal Mb.

MethodsI directly observed the oxygenation of Mb in perfused rat skeletal muscle under various states of tissue respiration. A computer-controlled rapid scanning spectrophotometer was used to measure the oxygenation of Mb in the transmission mode. The light beam was focused on the thigh quadriceps through a 5-mm-diameter light guide. The transmitted light was conducted to the spectrophotometer through another 5-mm-diameter light guide. Visible difference spectra in the range of 500–650 nm were recorded when O2 uptake in the hindlimb muscle reached a constant value after every stepwise change in the O2 concentration of the buffer.

ResultsThe O2 dissociation curve ODC of Mb, when the effluent buffer O2 pressure was used as the abscissa, was of a sigmoid shape under normal and increased respiratory conditions whereas it was of rectangular hyperbolic shape under a suppressed respiratory condition. The dissociation curve was shifted toward the right and became more sigmoid with an increase in tissue respiration activity. These observations indicate that an increase in O2 demand in tissues makes the O2 saturation of Mb more sensitive to O2 pressure change in the capillaries and enhances the Mb-mediated O2 transfer from Hb to cytochrome oxidase Cyt. aa3, especially under heavy O2 demands.

ConclusionThe virtual cooperativity and O2 demand-dependent shifts of the ODC may provide a basis for explaining why Mb has been preserved as monomer during molecular evolution.

Electronic supplementary materialThe online version of this article doi:10.1186-1476-5918-5-3 contains supplementary material, which is available to authorized users.

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Autor: Akitoshi Seiyama


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