Interaction of 13CO2 and Bicarbonate with Human Hemoglobin Preparations

• Main Authors: Morrow, Jon S., Keim, Philip, Visscher, Ronald B., Marshall, Robert C., Gurd, Frank R. N.
• Format: Text
• Language: English
• Published: 1973
• Subjects: Biological Sciences: Biochemistry; Sperm whale
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC433509; http://www.ncbi.nlm.nih.gov/pubmed/4514311

Formation of 13C-resonances attributable to carbamino derivatives has been observed in human erythrocyte hemolysate preparations equilibrated with 13CO2 at 33°. Carbamino formation is most marked in deoxyhemoglobin and at alkaline pH, and is very largely inhibited by the addition of 2,3-diphosphoglycerate or conversion to oxyhemoglobin. The prominent carbamino resonance at 30.0 ppm upfield of CS2 is visible in the spectrum of packed, deoxygenated erythrocytes equilibrated in 13CO2. This chemical shift falls close to that observed with sperm-whale myoglobin and within 2 ppm upfield of that seen with simple amino acids and peptides. The bicarbonate-carbonate resonance near 33 ppm is broad in the hemoglobin preparations, which always contain some carbonic anhydrase, but becomes narrow in the presence of the carbonic anhydrase inhibitor, acetazolamide. The nuclear magnetic resonance condition of intermediate exchange rate with dissolved CO2 (68.4 ppm) obtains in the absence of inhibitor. The process has marked consequences in reducing the spin-lattice relaxation time, T1, of the bicarbonate resonance by more than 10 times. The deoxyhemoglobin carbamino resonance has a T1 value of 700 msec, indistinguishable from that of the protein carbonyl resonance envelope.