THE QUANTITATIVE CYTOPHOTOMETRIC ANALYSIS OF TYROSINE BY A MODIFIED DIAZOTIZATION-COUPLING METHOD

In all of its aspects, both cytological and chemical, the diazotization-coupling method for tyrosine seems to approach quite closely the requirements for a cytophotometric method. It is highly specific, and this specificity is dependent only upon the inherent chemical properties of the tyrosine aromatic-OH group. It forms a pigment which has its maximal amplitude in a region near that of the maximal sensitivity of the human retina, allowing cellular areas to be readily seen, and which can be measured by simple photometric apparatus. It obeys Beer's law over the concentrations of tyrosine found in tissue sections and probably beyond. Its stoichiometry is known from calculations dealing both with a model protein system and with mammalian tissues. The in situ reaction product does not fade, and the procedure whereby it is deposited in sections is highly reproducible. Its only disadvantage seems to be the necessity of carrying out the diazotization step in an environment that is both cold and dark.