Effect of tetraphenylboron on the calcium-dependent ATPase activity of sarcoplasmic reticulum.

The apparent effect of tetraphenylboron on the Ca2+-dependent ATPase activity is rather complex being dependent of the physical state of the membrane. In leaky vesicles, tetraphenylboron decreases the affinity of the enzyme for Ca2+, and high concentrations (100 microM) inhibit the enzyme. These effects are mediated by the membrane structure. In native vesicles, tetraphenylboron induces an apparent stimulation of the maximum hydrolytic activity and a decrease of the Ca2+ gradient formed due to specific Ca2+ releasing activity of the mentioned drug.