The MSH-like substance in the urine of patients with retinopigmentosis, differing from that in normal persons, has no melanocyte-expanding effect, nor other physiological actions. In order to examine their difference physicochemically, adipokinetic activity of these substances were compared. While that from the normal person had the same activity as MSH, that from the patients lacked this tendency. Effects of the MSH-like substances on the free fatty acid in plasma was analyzed by gas chromatography and the substance from the urine of patients showed considerable difference from that of normal persons, such as in increasing the amount of lauric acid. Examination of a difference between these substances in chemical structure showed that the substance from the patients' urine lacked methionine in the structural amino acids, which is present in that from normal persons. It was proved through the experiment on recovery of effect by cysteine reduction and by identification of methionine sulfoxide by paper chromatography that in the structure of the MSH-like substance from patients' urine, methionine portion is in the form of methionine sulfoxide.
