The Effect of Formaldehyde on the Isoelectric Points of Some Proteins, Determined by Microelectrophoresis.

Abstract

The action of formaldehyde on proteins is of practical as well as theoretical interest. Formaldehyde has long been used industrially to increase the water resistance of proteins, especially casein, in the fields of plastics and coatings. Formaldehyde is also extensively employed as a preservative and fixative for biological specimens and to block off the amino groups in the titration of the acid groups of proteins and amino acids.An appreciable literature has accumulated concerning the nature of the reaction of formaldehyde with proteins and amino acids. Since reviews on this subject are available (7, 10, 23), it will not be discussed in detail. All the theories possess in common the postulate that the formaldehyde reacts with the free basic (amino, guanidino, or imino) groups of the protein or amino acid, but they differ in the complexities of the structures proposed for the product.According to the postulated reactions, the free basic groups on the micelle or molecule are rendered relatively inactive by the action of the formaldehyde. This should lessen the positive charge on the micelle and result in a shift of the isoelectric point to a lower pH value, since at any given pH the protein is less basic than before.It has been demonstrated by Smith, Max, and Handler (21) that the points of minimum solubility of casein and soybean protein are shifted to lower pH values by the action of formaldehyde. Gerngross and Bach (4) found that in gelatin solutions containing 10 per cent formaldehyde the isoelectric point of one gelatin sample shifted from a pH of 5.05 to 4.6 and of another from 4.75 to 4.3, as determined by an electrophoretic transference technique. Also, Swyngedauw ( 22), from a study of electroosmosis in gelatin gels before and after formaldehyde treatment, claims that formaldehyde does not combine with gelatin on the acid side of the isoelectric point but does on the basic side. Mudd and Joffe (15) studied the modification of antibodies by formaldehyde and showed a shift to

Zone electrophoresis of poliovirus partially inactivated by formaldehyde

“…Formaldehyde is known to bind itself on to the terminal amino groups of protein particles and, in several cases, it has been found that the i.e.p. 's of formaldehyde-treated protein molecules were indeed lower than those of untreated molecules (Circle & Smith, 1941).…”