Study of mechanics

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V-type ATPase (V_0V_1) capable of ATP-driven H^+ pumping and of H^+ gradient driven ATP synthesis was isolated from a thermophilic eubacterium, Thermus ther-mophilus. When the enzyme was analyzed by gel electrophoresis in the presence of sodium dodecyl sul-fate, it showed eight polypeptide bands of which four were subunits of V_1. We also isolated the V_0V_1 operon, containing nine genes in the order of atpG-I-L-E-X-F-A-B-D, which encoded proteins with molecular sizes of 13, 43, 10, 20, 35, 11, 64, 53, and 25 kDa, respectively. The last four genes were identified as those for V_0 subunits ; atpA, B, D, and F encoded the A, B, γ, and δ subunits, respectively. The first five genes, atpG-atpX, were identified as genes for the V_0 subunits. The product of atpL, the proteohpid subunit, lacked a 19-amino acid presequence and, unlike V-type ATPases, contained two membrane-spanning domains rather than four. The hydrophobic 43-kDa product of atpl is the smallest member so far found of the eukaryotic 100-kDa subunit family. Its electrophoretic band overlapped with the band of the A subunit. Therefore, all the gene products were found in our purified V_0V_1. We isolated the A_3B_3 subcomplex reconstituted from the isolated subunits and the A_3B_3γ subcomplex from subunit-expressing Escherichia coli. Electron microscopic observation of these subcomplexes revealed that the γ subunit of V_1 filled the central cavity of A_3B_3 and might be central subunit, similar to the γ subunit of F_1ATPase.