Functional properties of hemoglobin immobilized in coacervates prepared from gelatin A and polyanionic carbohydrates

Abstract

Complex coacervation is a phenomenon of phase separation that may occur in a solution of positively and negatively charged polyions. The resulting two phases are distinguished by the total concentration of both polyions, with the concentrated phase often containing vesicular structures composed of the two polyelectrolytes. We have used this phenomenon in an attempt to-prepare a hemoglobin-based red blood cell analog. Hemoglobin-containing coacervate vesicles have been prepared from gelatin A and the polyanionic carbohydrates acacia, pectin, or dextranstilfate. Hemoglobin seems to be anchored into the vesicle walls through interaction of its polyanion binding site with the negatively charged residues on the carbohydrates. Oxygen binding by the immobilized HbA is reversible and cooperative, with p50 values at 20 degrees C of 2.8, 6, and 24 mm Hg for the acacia- (pH 7.5), pectin- (pH 6.6), and dextransulfate-(pH 6.6) derived coacervates. Kinetic studies on CO binding show that the rate of CO uptake by the coacervates (t((1/2)) = 13-27 ms at 0.5 mM CO) is similar to that of human erythrocytes.The HbA-containing coacervates slowly dissolve in isotonic salt solutions (145 mM NaCl, pH 7.4), but they can be stabilized by treatment with glutaraldehyde. Oxygen binding by HbA incorporated into the stabilized coacervates derived from dextran sulfate is very similar to oxy gen binding by human red blood cells: p50 = 26 mm Hg and n = 1.89 at 37 degrees C in isotonic salt. These results show how a novel approach, based on an old concept, has led to the preparation of immobilized HbA, with functional properties similar to those of intraerythrocytic HbA.

Complex coacervates of hyaluronic acid and lysozyme: Effect on protein structure and physical stability

“…A wide variety of complex coacervates systems have been reported and investigated in the literature, e.g. protein-protein [5,32], protein-polymer [13,31], nucleic acid-polymer [16,26,24] and nucleic acid-dendrimer [11,19]. A more complete overview can be found in recent review papers [14,30].…”

Humic acid protein complexation

“…HS-protein interaction may lead to modification of the protein structure and, consequently, to a change in its biological activity. The extent to which this occurs depends on the specific conditions (Brouwer et al, 1990;Wen and Dubin, 1997;Xia et al, 1997). Furthermore, binding to other substances makes proteins less susceptible to microbial degradation and this can be environmentally hazardous.…”

Effects of Protein−Polyelectrolyte Affinity and Polyelectrolyte Molecular Weight on Dynamic Properties of Bovine Serum Albumin−Poly(diallyldimethylammonium chloride) Coacervates

“…Coacervation not only is exhibited by oppositely charged polyelectrolytes but also occurs when one component is a charged colloidal particle, for example, a protein, micelle, or dendrimer . Coacervation does not appear to perturb the structure of the colloidal particle, inasmuch as complexation and coacervation with a polycation results in little or no change in a protein's helical content, binding to ligands, or pH titration curve, and only a modest change in enzymatic activity . Similarly, the absence of structural changes in micelles upon coacervation with a polycation is implied by the absence of any change in dye solubilization and is also supported by cryo-TEM observations .…”