Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Evaluating the contributions of desolvation and base-stacking during translesion DNA synthesis

DNA polymerases catalyze the insertion of a nucleoside triphosphate into the growing polymer chain using the template strand as a guide. Numerous factors such as hydrogen bonding interactions, base-stacking contributions, and desolvation play important roles in controlling the efficiency and fidelity of this process. We previously demonstrated that 5-nitro-indolyl-2'-deoxyriboside triphosphate, a non-natural nucleobase with enhanced base-stacking properties, was more efficiently inserted opposite a non-templating DNA lesion compared to natural templating nucleobases (E. Z. Reineks and A. J. Berdis, Biochemistry, 2004, 43, 393-404). The catalytic enhancement was proposed to reflect increased base-stacking interactions of the non-natural nucleobase with the polymerase and DNA. However, the effects of desolvation could not be unambiguously refuted. To further address the contributions of base stacking and desolvation during translesion DNA replication, we synthesized indolyl-2'-deoxyriboside triphosphate, a nucleobase devoid of nitro groups, and measured its efficiency of enzymatic insertion into modified and unmodified DNA. Removal of the nitro group reduces the catalytic efficiency for insertion opposite an abasic site by 3600-fold. This results from a large decrease in the rate of polymerization (similar 450-fold) coupled with a modest decrease in binding affinity (similar 8-fold). Since both non-natural nucleobases show the same degree of hydrophobicity, we attribute this reduction to the loss of base-stacking contributions rather than desolvation capabilities. Indolyl-2'-deoxyriboside triphosphate can also be inserted opposite natural nucleobases. Surprisingly, the catalytic efficiency for insertion is nearly identical to that measured for insertion opposite an abasic site. These data are discussed within the context of pi-electron interactions of the incoming nucleobase with the polymerase:DNA complex. Despite this lack of insertion selectivity, the polymerase is unable to extend beyond the non-natural nucleobase. This result indicates that indolyl-2'-deoxyriboside triphosphate acts as an indiscriminate chain terminator of DNA synthesis that may have unique therapeutic applications.     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.