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ADENOSINETRIPHOSPHATASE AND NUCLEOTIDE METABOLISM IN SYNAPTOSOMES OF RAT BRAIN 1
Author(s) -
AbdelLatif Ata A.,
Smith Jack P.,
Hedrick Nina
Publication year - 1970
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1970.tb02226.x
Subject(s) - atpase , synaptosome , chemistry , phosphotransferase , biochemistry , enzyme , adenine nucleotide , nucleotide , substrate (aquarium) , adenylate kinase , phosphatase , microsome , atp hydrolysis , biology , in vitro , ecology , gene
—In the presence of synaptosomes prepared from rat brain, only ATP, dATP and ADP but not dADP were active as substrates of phosphatase (ATP phosphohydrolase; EC 3.6.1 4) in the presence of 150mm‐Na + and 20mm‐K + . An active adenylate kinase (ATP:AMP phosphotransferase; EC 2.7.4.3.) was demonstrated in the synaptosomal fractions by means of paper chromatography, paper electrophoresis and enzymic reactions, so that the high activity with ADP as substrate could represent an activity of an ATPase. Apparently dADP was not a substrate for the kinase; no dATP was formed when dADP was incubated with the synaptosomal fraction in the presence of Na + , K + and Mg 2+ . Small amounts of P 1 were liberated with dADP, IDP, GDP or CDP, but not UDP, as substrates, but none was produced in the presence of mononucleotides. The adenine‐deoxyribose bond, but not the adenine‐ribose bond, was hydrolysed upon the addition of 5% (w/v) TCA to the reaction mixture. The K M for the hydrolysis of ATP but not ITP, in the presence of Mg 2+ , or of Na + , K + and Mg 2+ , was lower for the synaptosomal ATPase than for the microsomal ATPase, and the values for V max for synaptosomal ATPase were higher. The activation increment was generally higher for the synaptosomal ATPase and no distinct differences in the properties of the enzyme from either particulate fractions were observed. Mg 2+ could be partially replaced by Mn 2+ in the synaptosomal ATPase system, but there was little Na + ‐K + ‐activation observed in the presence of the latter. The effects of ouabain and of homogenization under various conditions suggested localization of the K + ‐sensitive site of the ATPase on the surface of the synaptosomal membrane. Activity of the Na + ‐K + ‐Mg 2+ ATPase increased after freezing and thawing of the sonicated, sucrose or tris‐treated preparations but decreased considerably in the synaptosomes treated with 001 m‐deoxycholate. Activity of the Mg 2+ ATPase in the latter preparation showed little change.