類人猿におけるペプシノゲン遺伝子の多様性

抄録

Apes including gibbon, orangutan, gorilla, and chimpanzee are basically herbivorous, eating leaves and buds of trees, fruits, etc, that are common food habits to most of primates. In chimpanzees diversified food habits are appreciable since they occasionally hunt animals and eat them. Not only morphological adaptation but also molecular adaptation of digestive enzymes might be necessary to adapt new food habit. Gastric pepsinogen levels in apes are similar to those in the other herbivorous primates, being highest between gastric levels of mammals. This shows that a lot of pepsinogen is needed in apes to digest herbaceous foods containing high amounts of inhibitory materials such as cellulose and polyphenols. In adult ape stomach, two types of pepsinogens, i.e., pepsinogens A and C, are expressed. Although only one isozymogen is found in pepsinogen C, there are many isozymogens in pepsinogen A, being 9, 16, 8, and 14 isozymogens in gibbon, orangutan, gorilla, and chimpanzee, respectively. Since most of respective cDNAs have been cloned in orangutan, these isozymogens might be product of different genes. This suggests that some particular events such as duplication of pepsinogen gene occurred several times during the evolution of apes. Ape type-A pepsinogens are classified to two subtypes, i.e., high-Lys and low-Lys subtypes. The former subtype is found only in primates. The diversity and multiplicity of type-A pepsinogens in apes are thought to be useful for the effective digestion of various foods and might be essential for the evolution of apes.