Evaluation of two protein end-group reactions as potential fluorescent cytochemical methods

Histochemical preparations stained by a variant of the Morel-Sisley reaction for protein tyrosine were found to produce a red fluorescence when excited by broadband blue light which is topologically identical to the distribution of chromophore when viewed by absorption (equal transmission) microscopy. The fluorescence mode of viewing preparations stained by this method gave greater sensitivity and contrast than the absorption mode. The p-dimethylaminobenzaldehyde (DMAB)-nitrate method for protein tryptophan did not result in a useful fluorescent end-group method. Preparations stained by this method displayed a pattern of generalized fluorescence of all structures except those which react in the final step of the p-DMAB-nitrite reaction. The specificity of the intermediate reaction product has yet to be established.