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First published online June 11, 2007
Journal of Experimental Biology 210, 2082-2090 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003947
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Myoglobin-enhanced oxygen delivery to isolated cardiac mitochondria

Jonathan B. Wittenberg and Beatrice A. Wittenberg

Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461, USA

*Author for correspondence (e-mail: jwitten{at}post.harvard.edu)

Accepted 26 March 2007

The heart, red skeletal muscles and the nitrogen-fixing legume root nodule function in steady states of high oxygen influx, partial oxygenation of cytoplasmic myoglobin or leghemoglobin and correspondingly low oxygen partial pressure. Here, we ask: what conditions are required at the surface of actively respiring, state III, tightly coupled mitochondria to enhance oxygen flow to cytochrome oxidase? Pigeon heart mitochondria were isolated with minimal damage to the outer mitochondrial membrane and were incubated at low oxygen pressures, where respiration is oxygen limited, with solutions of each of six monomeric hemoglobins with widely divergent kinetics and equilibria in their reactions with oxygen: Busycon myoglobin, horse myoglobin, Lucina hemoglobins I and II, soybean leghemoglobin c and Gasterophilus hemoglobin. Each augments oxygen uptake. The declining fractional saturation of each hemoglobin with oxygen was monitored spectrophotometrically as mitochondrial respiration depleted the oxygen; the oxygen partial pressure at half-maximal rate of oxygen uptake was similar for each hemoglobin, supporting the conclusion that the hemoglobins did not interact with the mitochondrial surface in oxygen delivery. The oxygen pressure required to support state III mitochondrial oxygen uptake, 0.005 kPa (0.04 torr), is small compared with that obtained in the sarcoplasm and at the mitochondrial surface of the working heart, 0.32 kPa (2.4 torr). We conclude that, in normal steady states of contraction of the myoglobin-containing heart, oxygen utilization by mitochondrial cytochrome oxidase is not limited by oxygen availability.

Key words: myoglobin, oxygen, facilitated diffusion, heart, muscle, isolated cardiac mitochondria, cytochrome oxidase, pigeon


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OXYGEN UPTAKE IN MITOCHONDRIA

JEB 2007 210: i. [Full Text]  



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