Retention of Nitrogenous Material in Unfixed Sections during Incubation for Histochemical Demonstration of Enzymes

Abstract

THE dilemma of enzyme histochemistry is that if the tissue is not fixed, to avoid denaturation, the enzymes may dissolve out of the section into the incubation medium but, conversely, if the tissue is fixed to stop such loss of soluble enzymes, the fixation will inhibit activity and cause generalized denaturation. Thus, for most enzymes, it is argued that too much of the ‘soluble’ or lyo-form of otherwise bound enzymes¹ will be lost from unfixed sections during incubation in an aqueous medium; consequently it is considered advisable to fix the tissue prior to such incubation^1–3. Although it is usually conceded that the histochemistry of dehydrogenases depends on the use of unfixed sections, some⁴ have argued that even these should be studied in fixed tissue. Consequently it follows that the scientific basis of enzyme histochemistry must remain uncertain as long as a considerable loss of the activity to be investigated must be expected, whether this is caused by solution into the medium from unfixed sections, or from inhibition of activity produced by the preparative procedures.