Effects of hydration in the oxygenation and autoxidation of carbonmonoxyhemoglobin powder

The oxygenation and autoxidation of lyophilized human carbonmonoxyhemoglobin (Hb-CO) kept in environments with different relative humidities were followed with time using visible absorption spectroscopy. The sample kept at 68% relative humidity was the one with the greatest formation of methemoglobin (Met-Hb), while for increasing or decreasing hydrations the Met-Hb content decreased gradually. Besides the presence of Met-Hb, it was observed that the samples kept above about 68% relative humidity were converted to oxyhemoglobin (Hb-O2), the samples kept in the range 45-68% relative humidity were a mixture of Hb-CO and Hb-O2, while the samples kept below about 45% relative humidity and the solution sample continued as Hb-CO. Hemoglobin has, therefore, two critical hydration values, 45% and 68% relative humidity, which correspond to about 0.12 and 0.18 g H2O/g protein, respectively.