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  • Title: High-affinity binding of NADPH to camel lens zeta-crystallin.
    Author: Bazzi MD, Rabbani N, Duhaiman AS.
    Journal: Biochim Biophys Acta; 2001 Jan 12; 1544(1-2):283-8. PubMed ID: 11341937.
    Abstract:
    Fluorescence spectrum of camel lens zeta-crystallin, a major protein in the lens of camelids and histicomorph rodents, showed maximum emission at 315 nm. This emission maximum is blue shifted compared to most proteins, including alpha-crystallin, and appeared to be due to tryptophan in highly hydrophobic environment. Interaction of NADPH with zeta-crystallin quenched the protein fluorescence and enhanced the fluorescence of bound NADPH. Analysis of fluorescence quenching suggested high-affinity interaction between NADPH and zeta-crystallin with an apparent Km<0.45 microM. This value is at least an order of magnitude lower than that suggested by activity measurements. Analysis of NADPH fluorescence showed a biphasic curve representing fluorescence of free- and bound-NADPH. The intersection between free- and bound-NADPH closely paralleled the enzyme concentration, suggesting one mole of NADPH was bound per subunit of the enzyme. Phenanthrenequinone (PQ), the substrate of zeta-crystallin, also was able to quench the fluorescence of zeta-crystallin, albeit weaker than NADPH. Quantitative analysis suggested that zeta-crystallin had low affinity for PQ in the absence of NADPH, and PQ binding induced significant conformational changes in zeta-crystallin.
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