[Interaction of tertiapin, a neurotoxin from bee venom, with calmodulin]. / Vzaimodeístvie tertiapina, neirotoksina iz iada pchely, s kal'modulinom.

Tertiapin, a neurotoxin from the honey bee venom, interacts specifically with calmodulin in the presence of Ca2+. The nature of this interaction was studied using calmodulin-cAMP phosphodiesterase system. Tertiapin does not affect the unstimulated basal activity of phosphodiesterase. However, it totally inhibits the enzyme-activating capacity of calmodulin. Analysis of the dose-dependent activation of phosphodiesterase by calmodulin in the presence of tertiapin indicated that inhibition is caused by the interaction of two tertiapin molecules with calmodulin (Kd 2 microM). The data obtained suggest that the toxic effect of tertiapin in nervous tissue is mediated by blockade of calmodulin function.

[Membranes of bacteria and mechanism of action of the antibiotic gramicidin S]. / Membrany bakterii i mekhanizm deistviia antibiotika gramitsidina S

The cyclopeptide antibiotic gramicidin S taken at a concentration of 100--200 mkg/mg membrane protein rapidly increases the permeability of M. lysodeikticus protoplast membranes for substrates of respiratory chain and exogenous cytochromes c. Prolonged incubation of gramicidin S with protoplasts results in their lysis which is more fast at low temperatures. In contrast to natural gramicidin, a derivative of gramicidin S with acetylated amino groups does not inhibit either the micrococcus membrane dehydrogenase or the whole of respiratory chain and does not affect the osmotic barrier of protoplasts. Aliphatic diamines (at concentrations up to 0.1 M) and Ca2+ ions (10(-2) M) do not affect the functioning of the respiratory chain in isolated micrococcus membranes. Another derivative of the antibiotic with an increased distance of loaded amino groups from the cyclopeptide framework (diglycyl gramicidin S) affects the membrane in a way similar to that of natural gramicidin. Washing of gramicidin-treated membranes with NaCl enhances the inhibitory effect of the antibiotic on membrane enzymes. The data obtained suggest that in addition to ionic interactions some hydrophobic interactions also occur during gramicidin S binding to the bacterial membrane, probably at the expense of a hydrophobic peptide ring. It is assumed that gramicidin S, similar to Ca2+ and some other membranotropic agents provides for phase separation of negatively charged phospholipids from other groups of phospholipids, manifesting itself in an appearance of "frozen" sites on the membrane which destroys its barrier properties. This is due to the formation of ionic bonds of negatively charged phospholipids. Simultaneously, unlike Ca2+, gramicidin S, when interacting with membrane proteins, prevents their redistribution in more liquid parts of the membrane, which results in a situation when the respiratory enzymes become surrounded by alkyl chains with restricted motion.