A previous in vitro study by Vadas and Perelman (19) reported
an AC/protein ratio of 200:1 as necessary to achieve complete
binding of protein by AC. A pH value of 3.5 was used to mimic
gastric conditions, but normal stomach pH is much lower. The
protein-AC mixtures were incubated at 22 C, a nonphysiologically
relevant temperature. Subsequent findings from this laboratory
have shown that the adsorption of protein onto AC increases
progressively with temperature (20). Experiments at 37 C not
only represent physiological temperature but also increase protein
binding to AC. The AC used by Vadas and Perelman was
obtained by centrifuging a commercial suspension of AC in water.
Even though excess water was discarded, a large proportion of the
mass of the wet AC would be due to water. If the amount of AC is
measured via the volume of a suspension, because AC is not
soluble and settles quickly, an aliquot can contain significantly less
AC. Although AC administered in a clinical setting is in slurry
form, the AC in the experiments presented in the current investigation
was weighed as a dry powder so its mass could be determined
exactly. These factors may explain the apparent discrepancy
between the 200:1 AC/protein ratio required for complete
adsorption reported by Vadas and Perelman and the 80:1 ratio
reported both here and in a previous publication (20).