Abstract
A comprehensive study of the behavior of methemoglobin A, methemoglobin S, and metmyoglobin to adsorption and desorption of H 2O and D 2O vapor was conducted with the use of a McBain gravimetric sorption system. Additional information was sought from H 2O adsorption isotherms on cyano- and azido-methemoglobin A. All isotherms were conducted at 28° C. In all the adsorption isotherms a change in slope of the straight-line portion was observed to occur between 14 and 15 mm vapor pressure. The adsorption isotherms of cyano- and azido-methemoglobin A proved that this change in the rate of vapor adsorption was not associated with the transformation of anhydromethemoglobin to methemoglobin. Twelve BET plots were constructed from the isotherm data. BET monolayer coverage was significantly greater for metmyoglobin and cyano- and azido-methemoglobin A than for methemoglobin A. D 2O monolayer coverage was almost exactly the same as H 2O monolayer coverage for all heme proteins studied in both vapors. For all the isotherms studied in a given experiment a constant relationship was found between the amount of D 2O or H 2O adsorbed at the point where the slope of an isotherm changed and the quantity required for monolayer coverage of the adsorbent.
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