David H. Berg

Hexosamine interference with the determination of protein by the Lowry procedure

Abstract 1. 1. d -glucosamine and d -galactosamine and their corresponding N-acetyl derivatives interfere in the determination of protein by the Lowry assay. 2. 2. At the level of 0.5 mg/ml of free hexosamine, d -glucosamine gave an apparent protein level of 0.055 mg/ml and d -galactosamine, 0.070 mg/ml. At 2.0 mg/ml hexosamine, the respective values were 0.128 mg/ml and 0.220 mg/ml. 3. 3. The N-acetyl derivatives yielded approximately one-fifth of these values. 4. 4. Chondroitin 6-sulfate does not interfere with the Lowry protein assay.

Ionophorous properties of narasin, a new polyether monocarboxylic acid antibiotic, in rat liver mitochondria

Abstract Narasin, a new polyether monocarboxylic acid antibiotic, inhibits ATPase and reverses swelling and H+ release from liver mitochondria after induction of cation transport. Among alkali metal cations, narasin shows ionophorous activities with a selectivity of Na+ K+ = Rb+ Cs+ Li+. However, narasin also induces permeability of mitochondria to the non-noble gas cation, Tl+ and the polyatomic cation, NH4+. In fact, the polyether monocarboxylic acid ionophores, narasin and monensin, are more appropriate ionophores for NH4+ than for alkali cations. Narasin inhibits 50 per cent of the ATP hydrolysis activated by dinitrophenol, valinomycin-K+ and monazomycin-K+-NH4+ with ic 50 values of 2.5, 200 and 13 nM respectively. The corresponding ic 50 values for monensin are 7, 750 and 45 nM. The polyether monocarboxylic acid ionophores may play an important role in ionophore-producing organisms as NH4+ carriers.