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871.
Energetics of left and right handed models of DNA 总被引:1,自引:0,他引:1
It has been shown by model building studies that various right handed and left handed models are compatible with X-ray data of B-DNA and C-DNA. These models are also found to be in good agreement with infrared dichroism data. Detailed potential energy calculations have now been carried out for these models, viz., right and left handed B-DNA and right and left handed C-DNA. It is found that base sugar stacking and interactions involving the phosphate groups are the dominant forces for stabilizing a particular structure. For some sequences, viz., A-A, T-A and C-A, left handed stacking is quite favourable in both B and C structures. But intranucleotide interactions make the left B-DNA unfavourable while the left C-DNA structure is more stable, for all the sequences, than the right C-DNA structure, proposed from fibre data. For the hexanucleoside pentaphosphate fragments the same trend is observed, with the right handed B-DNA being the most stable of the four models studied. However, the left C-DNA structure is only marginally higher in energy, particularly if the shielding effect of the counter ions, on the phosphate group is taken into consideration. 相似文献
872.
873.
Goat sperm lysate from cauda epididymis was incubated in the presence of [14C]phosphatidyl-choline, -ethanolamine, -inositol and diphosphatidyl-glycerol. The release of [14C]diacylglycerol from only phosphatidyl inositol confirmed the presence of phosphatidyl inositol specific phospholipase C. The enzyme activity was linear up to 1 hr of incubation at a sperm concentration of 1-10 x 10(9). It had pH optimum of 7.5 in a broad range of pH activity profile (pH 6-9). Maximum activity was observed at 8 mM calcium ion concentration. EDTA and EGTA (5 mM) did not inhibit the activity completely. A comparative study on spermatozoa and fluid from caput, corpus and cauda epididymis revealed 6.5-fold increase of activity in spermatozoa and a 4-fold decrease in case of fluid during the epididymal transit. However, the total protein content remained unchanged in fluid and decreased up to the extent of 2.4-fold in spermatozoa during this process. Thirty five percent of the caudal sperm activity was soluble and the rest was associated with head (44%), mid-piece (10%) and tail (10%). 相似文献