[Rhabdomere adenosine triphosphatase systems of the squid Todarodes sloanei pacificus]

Highly purified fraction of squid photoreceptor membranes exhibits relatively low activity of Na+,K+-ATPase. No correlation was observed between the distribution of rhodopsin and Na+,K+-ATPase activity among photoreceptor membrane subfractions obtained from rhabdomeres. On the basis of these data, it is suggested that Na+,K+-ATPase and rhodopsin are localized in different membrane structures. In most purified fractions of rhabdomeres, the ratio of rhodopsin to total protein amounted up to 45--50%. In Triton X-100 extracts from membrane fractions, significant enrichment in rhodopsin content was observed.