The single histidine residue (His-15) in hen egg white lysozyme (EC 3.2.1.17) was chemically modified by diethyl pyrocarbonate (DEPC) to form exclusively the mono-N-carbethoxyimidazole adduct (second order rate constant of 252 +/- 16 M-1 min-1). Irreversible biscarbethoxylation of the His-15 imidazole ring by DEPC was observed when lysozyme was pretreated with 2-mercaptoethanol (2-ME), 2-ME plu...

Diethyl pyrocarbonate was used to modify histidyl residues on the sarcoplasmic reticulum ATPase. Difference spectra of the N-carbethoxyhistidyl derivative indicated that most all the histidyl residues on the enzyme had been modified. These residues could be divided into two populations on the basis of their reaction rate with the reagent. It could then be shown that enzyme inhibition followed m...

The chemical probes potassium permanganate (KMnO4) and diethylpyrocarbonate (DEPC) can be used to study the conformational flexibility of short tracts of adenine (A-tracts) present in DNA. With these probes, we demonstrate that a novel distortion is induced in a 5 base pair A-tract at low temperature. Formation of this distorted A-tract structure, which occurs in a DNA fragment from the promote...

Efficient mechanisms of H(+) ion extrusion are crucial for normal NADPH oxidase function. However, whether the NADPH oxidase-in analogy with mitochondrial cytochromes-has an inherent H(+) channel activity remains uncertain: electrophysiological studies did not find altered H(+) currents in cells from patients with chronic granulomatous disease (CGD), challenging earlier reports in intact cells....

The chemical modification of phosphoenolpyruvate carboxylase purified from Crassula argentea leaves was studied using the fluorescence of the extrinsic probe 8-anilino-1-naphalenesulfonate. The effects of ligands on kinetic parameters of phosphoenolpyruvate carboxylase activity, and its response to pH and metal cations, were associated with the binding of the ligands to the enzyme as measured b...

ABSTKACT: Choline acetyltransferase (EC 2.3.1.6) catalyzes the biosynthesis of acetylcholine according to the following chemical equation: acetyl coenzyme A + choline + acetylcholine + coenzyme A. Ethoxyformic anhydride inactivates the enzyme prepared from bovine brain. Acetyl coenzyme A and coenzyme A, but not choline or acetylcholine, substantially protect against inactivation. The enzyme is ...

Dihydrofolate reductase has been isolated and purified to homogeneity in g6od yield from two trimethoprim-resistant strains of Escherichia coli K12, strains MB 3746 and MB 3747. The two enzymes are closely related to one another and to the dihydrofolate reductase from E. coli MB 1428. The 3746 and 3747 reductases both exhibit an apparent molecular weight of 17,500 with almost identical amino ac...