Magnetic Susceptibility of Hemoglobin

A low-field low-noise SQUID magnetometer was built to measure magnetic susceptibilities. This system could measure the volume susceptibilities of samples at 20(DEGREES)C with an error of 0.1% the susceptibility of water. This performance was achieved only after a thorough investigation into noise mechanisms was performed. Calculations show an expected zero-field noise of (+OR-)0.002 fluxoids RMS/(Hz)(' 1/2), in excellent agreement with the observed noise of (+OR-)0.003 fluxoids peak/(Hz)(' 1/2). The susceptibilities of various hemoglobin preparations were determined at 20(DEGREES)C using this system. Human hemolysate, human stripped hemoglobin, and carp stripped hemoglobin with oxygen or carbonmonoxide as the ligand provided no evidence for electronic excited states. All results are consistent with the assignment of low spin ferrous to the iron site in these compounds. A consistent value for the mass susceptibility of diamagnetic hemoglobins, -0.580((+OR-)0.010) x 10('-6) cm('3)/gram, was obtained.