Signal transduction systems for detection of surrounding information are the one of essential functions for life. One of these systems is the sensory system such as vision, olfactory and gustatory. The innate immune system is also fundamental to protect our body, which basically senses microbial components by receptor proteins. In order to elucidate the function of the key molecules in the signal transduction, we have studied it on the view of organic chemistry. Here, the results on the

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... g key compounds will be shown; one is 11-cis-retinal in a light-receptor rhodopsin essential in vision, and the others are bacterial lipopolysaccharide and peptideglycan in the innate immune system.