The diffusion coefficients of carbon monoxide and nitrogen in haemoglobin solutions

Abstract

Krogh's (1919a) measurements of the rate of diffusion of 02, N2, CO and CO02 through animal tissues have formed the basis of many calculations of the role of diffusion in physiological processes (see, for example, Krogh, 1919b;Hill, 1928;Roughton, 1932;Jacobs, 1935). No information, however, appears to exist as to the rate of diffusion of these dissolved gases through homogeneous solutions of proteins: the value of the diffusion coefficients of 02 and CO in concentrated haemoglobin solutions has, in particular, been a desideratum in the theoretical investigations of Roughton (1932) and Nicolson & Roughton (1951) on the rate of exchange of 02 and CO between the interior of the red blood cells and the surrounding fluid. At the concentrations found in the red cells, the haemoglobin molecules must, according to Perutz (1948), be practically touching and there should accordingly be both marked geometrical obstruction and viscous resistance to the passage of small molecules of dissolved gases between the large protein molecules. The relation between the value of the diffusion coefficients and the protein concentration is therefore also of some theoretical interest.In the present paper we have determined the diffusion coefficients of N2 and CO in haemoglobin solutions ranging from 0 to 45 g haemoglobin/100 ml., the latter concentration being appreciably higher than that usually found in the red cells. In the case of N2 there has been no complication from any simultaneous chemical reactions of the penetrating substance: with CO, on the other hand, there has, from time to time, been trouble from side reactions even when the concentrations of CO have been such as to ensure that the haemoglobin is at least 99.99 % saturated with CO. Fortunately for our present purpose, N2 and CO have the same molecular weight and are very similar in many of their physical properties, including solubility. A priori, their diffusion coefficients in haemoglobin solutions should be about the same: molecules has also to be taken into account. Perutz's work would appear to make the need for such an allowance very unlikely, but fortunately we have found it possible, by means of an alternative method to our main one of measuring the diffusion coefficients of CO in haemoglobin solutions, to obtain direct experimental evidence on this point. METHODS I. Diffusion apparatusIn most of the experiments diffusion was measured between a gas phase containing CO or N2 at 1 atm pressure, and haemoglobin solution containing these gases in solution, but at different partial pressures from those in the gas phase. The apparatus, which was specially designed for use in conjunction with the Van Slyke gasometric methods, is shown in Fig. 1. It consists essentially of a large glass tap, T (bore about 1 cm), one lead of which is closed at the end whilst the other is fused to a straight capillary bore tap, U, and also to a 3-way capillary bore tap, V, the 265 266 I. S. LONGMUIR AND F. J. W. ROUGHTON leads from which are inclined at angles of 1200 to each other. On the...

The equilibrium between carbon monoxide and sheep haemoglobin at very high percentage saturations

“…It is possible, however, that some of the erratic results observed in the early stages of developing the present technique might have been due to this factor, or indeed to the converse and equally deleterious possibility, namely irreversible disappearance of carbon monoxide in haemoglobin solutions fully saturated with CO. This last phenomenon was mentioned (and guarded against) by Longmuir & Roughton (1952) in their work on the diffusion coefficients of CO in haemoglobin solutions. 100 4+4L4q' where z' is the percentage saturation of haemoglobin with carbon monoxide, q is the carbon monoxide pressure and L4 is the equilibrium constant of the reaction Hb4(CO)3 + CO=lHb4(CO)4.…”

CO metabolism, sensing, and signaling

“…This process is influenced by the alveolar gas volume, ventilation, and Hb concentration [12]. Although CO displays a very high affinity for Hb, O 2 can compete with CO for the heme-Fe-atom binding [31]. Moreover, CO can be slowly oxidized to CO 2 by mitochondrial cytochrome c oxidase (COX) [32].…”

Diffusion coefficients of CO2 molecule and bicarbonate ion in hemoglobin solution measured by fluorescence technique.

“…In the Stokes approximation, f is proportional to the viscosity coefficient µ, yielding that D x,u=constant at a given temperature. LONGMUIR and ROUGHTON (1952) experimentally showed by using sheep blood that the product of the diffusion coefficient of nitrogen and the viscosity, DN2 xp, was not constant Japanese Journal of Physiology (1951) reported, on the other hand, that the Doe as well as DN, in the red cell could be evaluated by extrapolating the regression line of the diffusion coefficient against the observed viscosity in a low Hb concentration range. In his observation, too, the viscosity of Hb solution suddenly increased at about 60 % of red cell hemolysate (ca.…”

“…In the later stage of the study the iteration of the complicated simulation procedures was avoided by evaluating the Dco2 as an exponential function of the Hb concentration according to the data on the N2 and 02 diffusion coefficients of LONGMUIR and RoUGHTON (1952) and KLUG et al (1956). The function was given by Dc02[Hb]=2.4 x 10 x (0.14)EHbJ (cm2/sec),…”