Regional distribution of acetylcholinesterase in the right atria of humans and dogs.

The regional distribution of acetylcholinesterase in the right atrium was determined by quantitative chemical measurements on hearts obtained from 14 infant and 9 adult humans of autopsy, and 9 adult dogs after termination of acute animal experiments. The atrium and interatrial septum were dissected, and the appendage was cut along its fold from the ventricular border to the superior vena cava. The atrium was cut into 20 consecutive sections. Homogenates (10% w/v) were prepared, centrifuged, and the supernatants were used for the enzyme assay by the method of Ellman. The acetylcholinesterase concentration [AChE] was mapped by section, or the sections were grouped into areas and mapped. The results show that: 1) in the dog, [AChE] is significantly higher in the nodal regions as compared to the appendicular areas, which contain the lowest [AChE]; 2) in the human, the [AChE] distribution pattern is qualitatively similar between the adult and infant, and in contrast to the dog, the appendicular areas contain the highest [AChE]; 3) for all areas studied, human infant [AChE] levels are significantly higher than human adult levels for corresponding areas. It is concluded that there is a distinct species difference between the regional distribution of the [AChE] in human and canine right atrium. Also, within humans, there is an age-related difference in the quantitative [AChE] levels. These species and age-related differences may reflect a varying pattern of distribution of the vagus nerve between the two species studied.

Effect of temperature on binding of warfarin by human serum albumin.

The in vitro binding of warfarin by human serum albumin was studied at various temperatures and at pH 7.4 by a frontal gel filtration technique. The results can be best described in terms of a two class-of-binding site model, in which the numbers of primary and secondary sites are constrained to the average values for all experiments (n1 = 1.38 and n2 = 3.73). Analysis of the temperature dependence of the binding yielded the following thermodynamic parameters: deltaH1 =-2.55 kcal/mole, deltaS1=16.1 eu, and deltaF1=-7.34 kcal/mole for the primary binding and deltaH2=-5.08 kcal/mole, deltaS2=-1.10 eu, and deltaF2=4.72 kcal/mole for the secondary binding. Calculations based on these results showed that, for the therapeutic concentration range, warfarin was over 99% bound to albumin present in physiological concentration. These findings are compared and contrasted to binding data in the literature for warfarin and salicylate.

Studies on the distribution of cholinesterases: activity in the human and dog heart.

The distribution and postnatal variation of cholinesterase (ChE) activity were studied in 25 human and 25 dog hearts. The observed distribution pattern is remarkably constant, In dog hearts, the pattern is as follows: sinus node (SN) greater than left atrium (LA) greater than right atrium (RA) greater than right ventricle (RV) congruent to left ventricle (LV). The average acetylcholinesterase (AcChE) activities as expressed in international units per g wet tissue are: 1.66 (SN), 1.14 (LA), 0.70 (RA), 0.22 (RV), and 0.21 (LV). In human hearts, the AcChE distribution follows the pattern of RA greater than LA greater than RV congruent to LV with corresponding average activities of 1.70, 1.38, 0.51, and 0.44 IU. The postnatal variation of ChE activity is most pronounced in the RS of the heart in both species. The average AcChE activity in the RA of the newborn puppies is 0.51 IU as compared with 2.27 IU in newborn infants. In the adult heart, however, the average atrial AcChE activity is nearly identical (1.02 IU) in both species. An additional difference is the large (34-64%) contribution of butyrylcholinesterase (BuChE) to the total activity in dog hearts whereas the contribution of BuChE is small (7-15%) in human hearts.

Gel filtration studies of oxyhemerythrin. I. Effects of pH on the association-dissociation equilibria.

The pH dependency of the dissociation of oxyhemerythrin has been studied by frontal gel chromatography on Sephadex G-75. The extent of dissociation is markedly pH dependent increasing below pH 6.0 and above pH 8.8. In addition, the nature of the dissociation reaction undergoes dramatic change with pH. Below pH 6.4 the rate of equilibration between species is slow relative to their time of passage through the column and they are thus resolved on chromatography. Above pH 6.6 the rate of equilibration is rapid and the various forms of hemerythrin are not resolved on migration through the column. Below pH 7.4 the dissociation is an all-or-none process with no detectable intermediates. Above pH 8.0 several intermediate species can be detected. Values for Keq and deltaG degrees are presented for various forms of oxyhemerythrin at the several pH's studied.

Gel filtration studies on oxyhemerythrin. II. Effect of temperature and ionic strength on the association-dissociation equilibria.

The effects of temperature and ionic strength on the association of oxyhemerythrin have been studied. deltaH degrees and deltaS degrees for association at pH 7.0 are -2.6 kcal and +16.5 eu per mol of monomer. These values suggest that solvent adjacent to the surface of the protein undergoes rearrangement on association. Increasing ionic strength is observed to promote dissociation while decreasing the rate of attainment of equilibrium between monomers and octamers. Qualitatively similar results are observed on lowering the pH from 7.0 to 4.8, thereby linking the effects of increasing ionic strength to those of protonation of specific amino acid residues at the subunit contacts of hemerythrin. The apparent enthalpy of ionization of the amino acid residue controlling dissociation at acidic pH was found to be -1.9 to +2.1 kcal/mol. These values are consistent with a carboxyl group.