Congo Red Fibrin Powder for Experiments on Proteolytic Enzymes

Abstract

STAINED fibrin substrates are sometimes used for experiments on proteolytic enzymes. Grutzner¹ used fibrin stained with carmine to estimate the amount of pepsin in a solution. Carmine fibrin cannot be used for testing for trypsin as the dye is dissolved out of the fibrin by alkalis. The difficulty was overcome by Roaf², who as early as 1908 used Congo red instead of carmine. Congo red is not dissolved out of the stained fibrin by hydrochloric acid or by sodium carbonate, and can thus be used for experiments on both trypsin and pepsin. Roaf first used a moist preparation which was preserved in equal parts of glycerol and water to which a little toluene was added. Later³ he used Congo red fibrin in the form of a dry powder, in which condition it kept well. Very little attention seems to have been paid to Roaf's work. Cole⁴, describes the use of carmine fibrin for an experiment on pepsin but does not mention Congo red fibrin. Hawk⁵ suggests the use of carmine fibrin for pepsin and Congo red fibrin for trypsin. These are both moist preparations which have to be preserved under ether or glycerol. The advantages of a dry stable powder which can be used for both pepsin and trypsin are obvious.