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Biomedical subjects

J Brahms

Publications and source records attributed to J Brahms.

At least 37 records · Page 2Linked to original sources
PubMed1975

Infrared linear dichroism investigations of deoxyribonucleic acid complexes with poly(L-arginine) and poly(L-lysine).

Complexes between DNAs from various sources and poly(L-lysine) and poly(L-arginine) were studied by means of infrared linear dichroism. The measurements of dichroic ratios allowed us to determine the orientation of the phosphate group of DNA in the complexes with basic polypeptides. At high relative humidities (higher than 90%, B form), the bisector of the less than OPO in the complexes forms an angle with respect to the helical axis which has a value lower by about 4 degrees than in the corresponding DNA sample. This change of orientation of the phosphate group of DNA indicates a modification of the B form upon binding of polylysine or polyarginine. The structural transitions B leads to A and B leads to C measured as a function of relative humidities were not affected by formation of complexes with both basic polypeptides. Similar results were obtained for complexes prepared by direct mixing or by salt gradient dialysis. The presence of A and C forms was observed in complexes of DNA with poly(L-lysine) and poly(L-arginine) at lower relative humidity. Thus, the conformational flexibility of DNA in complexes with polylysine and polyarginine is not changed despite a substantial increase in the Tm (melting temperature). These results are considered as a model for the understanding of interactions between DNA and histones particularly of the binding of the N-terminal fragment, lysine or arginine rich.

Arginine↗
PubMed1975

Conformations and structural transitions in polydeoxynucleotides.

Polydeoxynucleotides of different base sequence, the alternating poly[d(A-T)]-poly[d(A-T)], crab satellite DNA, on the one hand, and double-stranded homopolymer complexes poly[d(A)]-poly[d(T)], poly[d(I)]-poly[d(C)], on the other, display significant differences in their conformation and conformational transitions. Infrared linear dichroism investigations indicate that the alternating poly[d(A-T)]-poly[d(A-T)], enzymatically synthesized, adopts a lower humidity a well-expressed A* form in which stability is relatively small,i.e., restricted to limited relative humidity. This A form is characterized by the orientation of the bisector of the phosphate OPO group at 34 degrees with respect to the helical axis, which is slightly lower than that of DNA. In contrast, for the homopolynucleotide double-stranded complex poly(dA)-poly(dT) and also for poly(dI)-poly(dC), the B yields A conformational change is not observed. Instead poly(dA)-poly(dT) exists at lower humidity in a stable modified B form. Thus the present results indicate that homo(dA)-homo(dT) double-stranded sequences prevent the B yields A structural transition. All AT-containing polydeoxynucleotides and crab satellite DNA adopt a high humidity a modified B form characterized by the orientation of the bisector of the phosphate group OPO at 64 degrees with respect to the helical axis which is significantly lower than 68-74 degrees observed in DNAs. The base pairing geometry in poly(dA)-poly(dT), poly[d(A-T)]-poly[d(A-T)], and also in poly(dI)-poly(dC) is apparently a Watson and Crick type. Thus the observed differences in conformation are not due to different base pairing scheme. It is suggested that in DNAs of high AT content the presence of homo(dT)-homo(dA) sequences and the relatively low stability of the A form of d(A-T) alternating sequences may inhibit the change to the A form. A possible role of these sequences in DNA recognition by protein is suggested.

Binding Sites↗
PubMed1973

Direct evidence of the C-like form of sodium deoxyribonucleate.

From infrared linear dichroism studies, direct evidence is given for a new Na DNA form, which is similar to the C form of Li DNA. This C-like form in Na DNA occurs under conditions of very low NaCl content (at high relative humidity), high NaCl content (at low relative humidity), and low G + C content of the DNA (at low relative humitiy). The C form of Li DNA was originally discovered by x-ray diffraction, but has not previously been characterized by infrared spectroscopy. The C form is primarily characterized by the orientation of the O2- -O3 line of the phosphate group, which is about 48 degrees (+/-2 degrees ) with respect to the helical DNA axis and which is different from that of the B and A forms. Na DNA molecules rich in A + T may entirely or partially adopt the C form at low relative humidity. Since from infrared evidence, the C-like form is found not only in Li DNA at low relative humidity but also in Na DNA under different conditions, the C form may be biologically important. A possible role for recognition by proteins is suggested.

Adenine Nucleotides↗