A variety of techniques are currently in use for preparing protein-containing lipid vesicles known as proteoliposomes. However, the functionality of membrane protein in proteoliposomes prepared by various techniques has rarely been evaluated directly. We prepared rhodopsin-containing proteoliposomes consisting of asolectin or native retinal rod outer segment disk lipids using n-octyl beta-d-glucopyranoside and the detergent dialysis (DD) and rapid dilution (RD) techniques and measured the activity of rhodopsin using equilibrium UV/vis and flash photolysis spectroscopy. A significant difference in rhodopsin activity was observed in proteoliposomes prepared by these techniques. The equilibrium constant of metarhodopsin I-metarhodopsin II is 30-45% higher, and the apparent rate constant of MII formation is up to 3-fold faster in proteoliposomes prepared by RD vs DD. The DD technique produced larger yet more heterogeneous vesicles, while the RD technique yielded smaller and more homogeneous vesicles, as determined by electron microscopy and isopicnic centrifugation. Both proteoliposomes and empty lipid vesicles lacking rhodopsin were formed in the DD preparation, while only proteoliposomes were formed in the RD preparation. Under identical conditions, proteoliposomes prepared by RD have a higher L/P ratio, which is consistent with the higher level of rhodopsin activity in RD proteoliposomes. Overall, the results presented here suggest that the RD technique has an advantage over the DD technique in terms of preserving optimal rhodopsin activity and controlling the lipid to protein ratio in the final proteoliposomes.

Back in the early 1970s, Partha Dasgupta realized that the economic models of the time were neglecting an entire class of capital assets: natural resources. Over the course of his career, Dasgupta, an economist at the University of Cambridge and a foreign associate of the National Academy of Sciences, has worked to put "natural capital" on an equal footing with other capital assets, exploring how natural resources and human population underlie issues such as poverty and sustainability. Dasgupta has advocated for measuring the strength of national economies based on their "inclusive wealth," which includes the value of natural capital alongside infrastructure and human capital, rather than gross domestic product (GDP). Recently, Dasgupta cochaired "Moral Dimensions of Climate Change and Sustainable Humanity," a joint symposium of the Pontifical Academy of Sciences and the Pontifical Academy of Social Sciences. The report from that symposium informed Pope Francis' encyclical on climate change and the environment (1). In 2016, Dasgupta became the first economist to receive the Tyler Prize for Environmental Achievement. PNAS spoke with Dasgupta to commemorate the honor.

When people think of research at the National Aeronautics and Space Administration (NASA), sea ice may not be the first thing that comes to mind. Yet Claire Parkinson, a climate scientist at NASA's Goddard Space Flight Center in Maryland, has spent 4 decades studying sea ice. Parkinson's use of satellite data has revealed clear and sometimes unexpected long-term changes in Arctic and Antarctic sea-ice coverage. Meanwhile, as project scientist for NASA's Aqua satellite, she oversees the collection of data used by scientists around the world. Parkinson has received numerous honors for her accomplishments, including election to the US National Academy of Engineering in 2009 and the National Academy of Sciences in 2016. Claire Parkinson speaking at the Maryland Women's Heritage Center. Image courtesy of Steve Graham (photographer).

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