4-Nitro-1-cyclohexyl-3-ethoxy-2-oxo-3-pyrroline. A reversible, amino-specific, protein reagent

4-Nitro-1-cyclohexyl-3-ethoxy-2-oxo-3-pyrroline reacts with both amino and sulfhydryl groups. The instability of the product with sulfhydryl groups makes the reagent a useful amino-group specific protein reagent. The advantages of this compound include (1) rapid reaction with protein (less than 15 min at pH 9), (2) EASE OF REVERSAL UNDER MILDLY ALKALINE CONDITIONS (PH larger than or equal to 8) with formation of a water-soluble by-product (lambdamax = 363 nm), and (3) ease of quantitation utilizing the high extinction coefficients of the amino derivative (lambdamax = 383 and 397 nm, epsilon397 = 20 200 M-1 . cm-1) and the reversal by-product (lambdamax = 363 nm, epsilon = 16 300 M-1 . cm-1). With these characteristics and the stability of the amino derivative under physiological conditions (t1/2 for reversal = 167 h at pH 7.0 and room temperature), nitrocyclohexylethoxyoxopyrroline can be a useful reagent in a wide variety of protein sequencing and structure studies.