The study of the choleride and nitrate binding sites of the opsin of the 521-pigment of the Tokay gecko will be continued, attempting to identify the amino acids associated with these sites. This will be done by examining the effect of pH and of reagents known to bind to specific amino acids. The properties of the rhodopsin in the phagosomes of the frog retina will be examined and compared with those of rhodopsin in the outer segments. This will be done with the phagosomal rhodopsin in various stages of degradation within the outer segments. In this way the function of the pigment epithelium in relation to visual pigment turnover will be subjected to scrutiny.