Glyoxal fixation and its relationship to immunohistochemistry

Glyoxal is a popular Substitute for formalin and in many ways acts like it, although there are significant differences. When formulated correctly, glyoxal fixatives produce superior morphological detail in only 1-9 h, but crosslinking does not occur. Glyoxal has a unique reactivity with arginine, producing a cyclic imidazole in place of the highly charged guanidinium group, thus reducing eosinophilia ill arginine-rich tissue elements. In the absence of crosslink-induced masking of epitopes, most antibodies work directly on glyoxal-fixed specimens without the need for antigen retrieval. The arginine reaction does cause loss of immunoreactivity in arginine-rich antigens, however. Fortunately, the imidazole is readily removed by a simple antigen retrieval process: pH 8.6 Tris HCl buffer for 10 min at 125 degrees C. The conformational basis for needing antigen retrieval, and how it works on a Molecular level is explained for both glyoxal and formalin fixation.