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J. Horwitz, Q. Huang, L. Ding; Molecular Crowding in the Eye Lens . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2011.
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The eye lens is a unique organ with extremely high protein concentration reaching values of up to 500 mg/ml. The effects of "Macromolecular Crowding" in organs and in intact cells are well recognized, but relatively little research has been done in this area. The purpose of our research is to see what are the effects of molecular crowding on the activity and stability of some housekeeping enzymes under conditions that mimic the native in vivo environment. In addition we wanted to study the effects of high concentration of the lens crystallins on these enzymes, when compared to high concentration of non–specific proteins such as bovine serum albumin or ovalbumin.
Calf lenses were used for all experiments. We chose the enzyme glucose–6–phosphate dehydrogenase (G6PD). Enzyme activity was measured following standard methods of monitoring the reduction of NADP at 340 nm with total lens protein concentrations ranging from 5 mg/ml to 150 mg/ml.
G6PD activity was independent of the total proteins concentration in the eye lens. The high protein concentration protected the activity from thermal denaturation. At a total lens protein concentration of 150 mg/ml 92 % of the enzymatic activity remained following heating the solution to 45°C for 2 hours, whereas at 5 mg/ml only 27% of the activity remained. Bovine serum albumin at high concentration did not protect enzyme activity. Purified alpha, beta or gamma crystallin did not protect G6PD from thermal denaturation, however the native mixture of the crystallin did provide protection.
The high concentration of crystallin in the eye lens provides protection to enzymatic activity. A high concentration of non–specific proteins such as BSA and ovalbumin do not provide protection. Alpha, beta and gamma–crystallin must interact in some unknown manner to provide the protection and stability that the lens enzymes exhibit.
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