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(PROTEIN) WATER MOLECULE AMINO GROUP

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capillary all-trans RETINOL (t)<br />

*<br />

all-trans<br />

RETINYL<br />

(t)<br />

ESTER<br />

11-cis<br />

RETINOL<br />

all-trans<br />

*<br />

RETINOL<br />

*<br />

11-cis<br />

RETINAL<br />

(t)<br />

(t) (t)<br />

(t)<br />

all-trans<br />

RETINAL<br />

+<br />

11-cis OPSIN<br />

RETINAL<br />

+<br />

OPSIN<br />

all-trans<br />

RETINOL<br />

hν<br />

RHODOPSIN<br />

Color Plate 4<br />

The processing and transport of vitamin<br />

A at PE (pigment epithelial) cells and<br />

photoreceptor outer segments. ➤ At PE<br />

cells retinol may be stored as an ester or<br />

transported to the outer segment. The<br />

transport between and within PE cells<br />

and photoreceptor outer segments of<br />

11-cis retinal as well as between photoreceptor<br />

cells and PE cells of all-trans<br />

retinol makes use of other transport<br />

binding proteins (t), an interstitial retinol<br />

binding protein (IRBP) as well as an<br />

intracellular retinal binding protein<br />

(CRBP) as described by Hollyfield et al<br />

(1985). Metabolic transformations of the<br />

different vitamin A forms are enzymatically<br />

catalyzed (*) in both the PE and<br />

photoreceptor cells. See text for further<br />

explanations.<br />

*

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