Human exposure to sunlight promotes the formation of pre-vitamin D in the skin. Low or marginal levels of vitamin D has been linked to a wide range of human health outcomes, including the development of various types of cancer. However, few data exist on the actual exposure to human due to vitamin D producing ultraviolet radiation. Most studies of human disease and vitamin D have linked latitude and location of residence to expected exposure form the available ambient UV radiation. Human UV exposure for the development of vitamin D depends on a variety of factors such as time spent outdoors, percent available skin, skin type, UV protective devices used and distribution of UV over the human form. In this paper, we investigate how latitude impacts not only on the amount of UV available for vitamin D synthesis, but also the distribution of UV over the human form.

The conformational changes of a 22 base-pair double-stranded DNA, anchored via one end to a quartz substrate, have been characterized using a single-pair fluorescence resonance energy transfer technique. Base-pair mismatch, a major form of DNA damage, has been found to decrease the energy transfer between a fluorescence donor and an acceptor attached to the two ends of DNA molecules with 3 and 7 mismatches, by 4.4% and 10.4%, respectively, as compared to that for perfectly matched DNA. This result suggests that the disruption of the hydrogen bonds in damaged DNA leads to increased contour length and improved flexibility.

Endonuclease V (endo V) recognizes and cleaves deoxyinosine in deaminated DNA. These enzymatic activities are precursors of DNA repair and are fueled by metal ions such as Ca2+ and Mg2+, with the former being associated with protein binding and the latter with DNA cleavage. Using the technique of fluorescence resonance energy transfer (FRET), we determined the single-molecule kinetics of endo V in a catalytic cycle using a substrate of deoxyinosine-containing single-stranded DNA (ssDNA). The ssDNA was labeled with TAMRA, a fluorescence donor, while the endo V was labeled with Cy5, a fluorescence acceptor. The time lapses of FRET, resulting from the sequential association, recognition, and dissociation of the deoxyinosine by the endo V, were determined at 5.9, 14.5, and 9.1 s, respectively, in the presence of Mg2+. In contrast, the process of deoxyinosine recognition appeared little affected by the metal type. The prolonged association and dissociation events in the presence of the Ca2+-Mg2+ combination, as compared to that of Mg2+ alone, support the hypothesis that endo V has two metal binding sites to regulate its enzymatic activities.

No abstract