Retinol testis

Retinoic acid may either enter the target cell from the circulation or may be formed intraceUularly by oxidation of retinol. A number of tissues - but not muscle, kidneys, small intestines, liver, lungs, or spleen - have a cellular retinoic acid binding protein (CRABP) that is distinct from CRBP. Testis and... 

The absorption spectrum of CRABP with bound retinoic acid purified from rat testis (Ong and Chytil, 1978b) is shown in Fig. 3. The spectrum shows typical protein absorbance centered at 280 nm but is dominated by the peak at 350 nm from the bound retinoic acid. The spectrum of retinoic acid bound to CRABP is very similar to free retinoic acid in organic solution. The molar extinction coefficient for retinoic acid bound to CRABP is about 50,000. The value of AjjgMjgo for purified CRABP believed to be saturated with retinoic acid is 1.8. It is of interest that the absorption spectrum of the CRABP-retinoic acid complex is similar to that of the CRBP-retinol complex these spectra differ substantially from that of the RBP-retinol complex (see Chapter 8). 

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