ISSN:
1432-072X
Keywords:
Methanobacterium thermoautotrophicum
;
Nucleotide transport
;
Nucleotide binding
;
Protoplasts
;
Membrane vesicles
;
Methanochondrion concept
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract In order to test the “Methanochondrion concept”, uptake of adenine nucleotides in various membrane preparations of Methanobacterium thermoautotrophicum was studied. The uptake showed properties which are in general interpreted as indicative of a transport mechanism: (i) kinetics in the time range of minutes, (ii) temperature dependence, (iii) substrate specificity and (iv) failure to remove the substrate by extensive washing. However, nucleotide transport as an interpretation of this “uptake” can definitely be excluded. Not only an exchange mechanism of the mitochondrial type, but also a general exchange or an uniport mechanism was ruled out. In contrast, the “nucleotide uptake” was shown to be actually a tight and specific binding of ADP and ATP to binding sites at the interior side of the cell membrane. This was conclusively demonstrated in protoplasts obtained from M. thermoautotrophicum cells. In these protoplasts which do not contain internal membranes also nucleotide binding was observed, but only after disruption of the plasma membrane by osmotic lysis, which leads to the exposure of binding sites.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00410938
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