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. 2010 Sep;51(9):4351–4357. doi: 10.1167/iovs.10-5852

Figure 4.

Figure 4.

Bisretinoid formation in impaired photoreceptors can greatly exceed that generated in healthy photoreceptor cell outer segments. (A) HPLC quantitation of all-trans-retinal (retinoid precursor of RPE lipofuscin) and two bisretinoids (all-trans-retinal dimer and A2PE) that form in photoreceptor cells via the lipofuscin biosynthetic pathway. Eyecups of RCS and control (RCS rdy+) albino rats, age 1 month, included RPE and neural retina. Under normal conditions, phospholipase D-mediated phosphate hydrolysis of A2PE (dashed line in structure) in RPE cell lysosomes releases A2E, and the latter then accumulates in RPE. However, in the RCS rat, because of the failure to phagocytose, most of the pigment generated within the A2PE/A2E pathway remains as A2PE. (B) Fluorescence emission spectra of A2E and A2PE recorded at an excitation of 488 nm. The slightly greater fluorescence intensity of A2PE probably reflects an excitation maximum (∼449 nm) that is closer to 488 nm than the excitation maximum of A2E (∼439 nm).