The reaction of chloroacetaldehyde with single-stranded DNA (ssDNA) yields epsilon DNA, a highly fluorescent substance. The binding of recA protein to epsilon DNA nearly doubles its fluorescence yield. The enhanced fluorescence signals the formation of a recA-epsilon DNA complex. This complex exhibits an ATPase activity as great as that of the corresponding recA-ssDNA complex. Addition of a saturating concentration of adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) to a solution of the recA-epsilon DNA complex yields a further rise in fluorescence. Saturation with ATP produces the same rise. The nucleotide triphosphates have converted the recA-epsilon DNA complex into the respective ATP gamma S-recA-epsilon DNA and ATP-recA-epsilon DNA complexes. The fluorescence changes that accompany the formation of the three complexes have enabled us to (1) establish by titration that recA protein binds to 6.0 +/- 0.3 nucleotides of epsilon DNA, (2) show that the binding of ATP to the recA-epsilon DNA complex is highly cooperative under various conditions, with a Hill coefficient of 2.4-4.9 and Kapp = 25 +/- 2 micro M, (3) show that the binding of ATP gamma S is also highly cooperative, with a Hill coefficient of 3.3-4.2 and Kapp congruent to 0.5 micro M, and (4) perform initial measurements on the rate at which recA protein transfers between polynucleotides. The experiments provide the first direct observation of an ATP-recA-ssDNA-like complex, and they illuminate some of the properties of such complexes.

Fig. 3. This is a schematic representation based O I I [ivcrage R, values appearing iii 7 differerit rlironiatographic runs. I t is evident that the various antimycin A components were obtained in cliroiiiatographically homogeneous form. Further, from these results blastmycin appeared to consist mainly of antimycin A3 with minor contamination by the A4 component.Paper chromatogranis of the various antimycin complex preparations are also given in Fig. 3 . I t is apparent that the four antimycin preparations all contained at least the ill, An and A 3 components, although in somewhat varying proportions. Yirosin was similar in Composition but also contained a significant proportion of antimycin Aq. The other preparations may also have contained small amounts of A 4 as it certainly was present in the Harada sample but yet was not detected by the chromatogram.Infrared spectra of various preparations as shown in Fig 4 reveal extremely close similarity both of the individual components A1 and A3 to each other and to blastmycin and virosin. Antimycin A2 and the antimycin complex also gave essentially the same infrared spectrum. The differences are too slight to be of much aid in establishing differences in the chemical structure. Evi-dently, the components differ from each othcr only in the alkyl side chains of the neutral portioii of the molecule.3 Such a relationship is also suggested by the molecular formulas of AI, AB and A3 which differ among themselves only by the ey uivalen t of one to three methylene groups, The ultraviolet spectra of the individual components also were essentially identical.The infrared tracing of blastmycin offers further evidence of its very close similarity with antimycin; furthermore, its melting point was close to that of antimycin AB and the mixed melting point showed no depression. These data taken together with the above paper chromatographic results establish quite conclusively that the major coniponent of blastmycin is identical with antimycin AB and indicate that the minor component very probably is antimycin Ad.All three of the isolated antimycin A components showed neutral equivalents appreciably lower than theory for their most probable molecular formulas. This discrepancy may be attributable to partial cleavage of the alkali-sensitive bond of the antimycin A structure.13 The investigation of these and other aspects of the chemistry of antimycin A is being continued.Investigation of the extent of isotope-position rearrangement in carbonium ion-type reactions of I4C-labeled cyclopropylcarbinyl derivatives has revealed that the three methylene groups of the starting material achieve a striking degree of equivalence between reactants and products. These results, taken in conjunction with the abnormally large solvolytic reactivities oE cyclopropylcarbinyl and cyclobutyl halides and sulfonate esters, can best be accounted for by assuming rapid but not instantaneous equilibration of three isxneric rion-classical unsymmetrical "bicyclobutonium" ion intermediates.Considerable interest att...

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