A B S T R A C T Double-stranded DNA fragments of varying sizes were isolated and tested for binding to systemic lupus erythematosus (SLE) antinative DNA antibodies. Fragments of 20-25, 40-50, 90-110, and 160-180

A B S T R A C T Experiments were designed to determine the basis for the strong competitive reaction of denatured DNA with systemic lupus erythematosus (SLE) antinative DNA antibodies. Secondary structure in denatured DNA was reflected in hyperchromicity upon heating and in multiphase kinetics ofits digestion by Si nuclease. Partial digestion by Si nuclease completely eliminated the ability of denatured DNA to react with antidenatured DNA antibodies, but not its ability to react with SLE sera. Sl nuclease-resistant cores were isolated from extensively digested denatured DNA. These cores had secondary structure, including some stable fold-back helical regions. The cores, from 20 to several hundred base pairs in size, competed with native DNA for binding by SLE sera. Other experiments measured reactions of denatured DNA under conditions that affected its secondary structure content. Its competitive activity decreased as temperature was increased from 00 to 37°C, whereas the activity of native DNA was not altered in this temperature range. With DNA pieces of 90-110 base pairs, native fragments were much more effective than the denatured fragments, in which stable helical structure is less likely to occur than in high molecular weight denatured DNA. Competitive assays with mononucleotides, oligonucleotides, homopolymers, and RNA-DNA hybrids also indicated that two strands of polydeoxyribonucleotide were required for optimal reactions with these SLE serum antibodies. The antibodies can measure stable helical regions in denatured DNA; they may also stabilize short helical regions that occur in an equilibrium of conformational forms.

most of the drug would decompose. Thus decomposition products may be the reactive species in the system described by Dubroff and Reid. This criticism regarding stability has been made about other studies (7). (v) Hydralazine is known to concentrate (400:1, vessel concentration to plasma concentration) in blood vessels of animals after a dose of 14C-labeled hydralazine (7). Immunogenic reactions may be initiated in vessels, or their collagen (7). Collagen is known to have carbonyl groups capable of reacting with amino groups (8). (vi) Several reviews deal with hydralazi0(4, 7, 9, 10), and two cover physicochemical properties and assay methods in detail (7, 9). Thus Dubroff and Reid should consider the measurement of hydralazine in their experiments.

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