[The effect of antibodies against Ca2(+)-ATPase and its hydrophobic fragment on the activity of this enzyme and on the passive transport of Ca2(+)]. / Vliianie antitel protiv Ca2(+)-ATPazy i ee gidrofobnogo fragmenta na aktivnost' étogo fermenta i passivnyi transport Ca2(+).

It is shown that both Ca(2+)-ATPase and its hydrophobic fragment are immunogenic factors. A region between hydrophobic and hydrophilic parts of Ca(2+)-ATP-ase is immunogenic. These antibodies clearly inhibit inflow and outflow of Ca2+ through a hydrophobic fragment reconstructed into liposomes and do not influence Ca(2+)-ATPase activity.

The ion-conducting properties of Ca2+ ATPase in rabbit skeletal muscle sarcoplasmic reticulum.

Ca2+ ATPase was isolated from rabbit skeletal muscle sarcoplasmic reticulum and used to form structures resembling potential-dependent calcium channels within the membrane lipid bilayer of liposomes. The orientation of these structures in the bilayer was dependent on the conditions used for enzyme incorporation. The results obtained indicate that Ca2+ ATPase may be involved in the passive transport of calcium ions from the sarcoplasmic reticulum which may be regulated by the membrane potential. The membrane potential within the reticulum is probably positive at the moment of calcium ion release.

[Determination of AMP-aminohydrolase activity by a chromatographic method]. / Opredelenie aktivnosti AMP-aminogidrolazy khromatograficheskim sposobom.

A method is developed for determining the AMP-aminohydrolase activity by means of chromatography on the home KY-2 ion-exchange resin. It differs from the method of differential spectrophotometry by the fact that its application enables the content of IMP formed due to the enzymic reaction to be determined by its absolute quantity. This method yields satisfactory results independently of the substrate concentration. However, it cannot be applied for determination of the AMP-aminohydrolase activity in the presence of ATP.

[Efflux of Ca2+ from fragmented sarcoplasmic reticulum during AMP deamination]. / Osvobozhdenie ionov kal'tsiia iz fragmentirovannogo sarkoplaematicheskogo retikuluma pri dezaminirovanii AMP.

Deamination of AMP in skeletal muscle sarcoplasmic reticulum followed by an increase in pH from 6,5 up to 8,0 leads in a liberation of part of Ca2+ from the SR vesicles. This effect is enhanced by K+, which activate the deamination, and is suppressed by Mg2+, which inhibit the reaction. The activating effect of AMP on Ca2+ efflux from the vesicles markedly decreases after AMP deaminase dissociation from the vesicles and is restored after reconstitution of their deaminase activity. Substitution of IMP for AMP causes a decrease of Ca2+ efflux from the vesicles. The data obtained are in good agreement with the assumption that the ammonium formation from AMP can favour the release of Ca2+ from some vesicles of SR.

[Solubilization and reconstruction of microsomal AMP-deaminase from skeletal muscles]. / Soliubilizatsiia i rekonstruktsiia mikrosomal'noi AMP-dezaminazy skeletnykh myshts.

Microsomal AMP-deaminase was solubilized by 0.5 M KCl after treatment of microsomal membranes with 0.12 M KCl. Using disc-electrophoresis in polyacrylamide gel in the presence of sodium dodecyl sulfate one major protein component (mol. weight about 90 000) and three minor ones with molecular weights of 110 000, 80 000, and 60 000 were found in the soluble fraction. In addition to proteins, the fraction was found in the soluble fraction. In addition to proteins, the fraction was found to contain a small amount of phospholipids. The deaminase found in the solution may be reconstructed into the membranes at a decrease in KCl concentration, part of enzyme being bound in the inactive form under excess of the soluble fraction. Deaminase binding to the membranes is unaffected by the changes within the pH range of 6.2--7.8 and temperature range of 4--10 degrees C. It is assumed that AMP-deaminase is bound to other membrane components by electrostatic bonds.

[Distribution of the action of creatine kinase, AMP-aminohydrolase and ATPase,and absorption of Ca+n microsomal fractions of skeletal muscles].

The microsomal fraction of the rabbit skeletal muscles contains structures which absorb Ca2+ and where ATPase-aminohydrolase activities are pronounced. Electrophoresis of this fraction in the saccharose density gradient results in separation of a considerable amount of soluble proteins including creatine kinase, as a high ATPase activity and absorbing Ca2+ to an inconsiderable extent. The activity of creatine kinase in the microsomal fraction of the rabbit and rat skeletal muscles is not so high to provide for ATP regeneration from creatine phosphate in the amount sufficient for any considerable transport of Ca2+. In the microsomal fraction of the myocardium, as distinct from the skeletal muscles creatine kinase is strongly bound with its structural components and is not separated by electrophoresis.