Ida Takanori, Miyazato Mikiya, Naganobu Kiyokazu, Nakahara Keiko, Sato Miho, Lin Xing-Zi, Kaiya Hiroyuki, Doi Kentaro, Noda Soushi, Kubo Ayako, Murakami Noboru, Kangawa Kenji
Department of Veterinary Physiology, Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2155, Japan.
Domest Anim Endocrinol. 2007 Feb;32(2):93-105. doi: 10.1016/j.domaniend.2006.01.002. Epub 2006 Jan 23.
Ghrelin, a novel 28-amino acid peptide with an n-octanoyl modification at Ser3, has been isolated from rat and human stomach as an endogenous ligand for the growth hormone secretagogue receptor. Here, we purified feline ghrelin and examined its possible physiological role in cats. The major active form of feline ghrelin is a 28-amino acid peptide octanoylated (C8:0) at Ser3; except for one amino acid residue replacement, this structure is identical to those of rat and human ghrelins. However, much structural divergence in peptide length and fatty acid modification was observed in feline ghrelin: peptides consisting of 27 or 26 amino acids lacking Gln14 and/or Arg28 were found, and the third serine residue was modified by octanoic acid (C8:0), decanoic acid (10:0), or unsaturated fatty acids (C8:1, C10:1 and C10:2). In agreement with the structural divergence, two kinds of cDNA with different lengths were isolated. Administration of synthetic rat ghrelin increased plasma growth hormone levels in cats, with a potency similar to that in rat or human. Plasma levels of ghrelin in cats increased approximately 2.5-fold after fasting. The present study indicates the existence of structural divergence in feline ghrelin and suggests that, as in other animals, ghrelin may play important roles in GH release and feeding in cats.
胃饥饿素是一种新型的由28个氨基酸组成的肽，其丝氨酸3位带有正辛酰修饰，已从大鼠和人的胃中分离出来，作为生长激素促分泌素受体的内源性配体。在此，我们纯化了猫的胃饥饿素，并研究了其在猫体内可能的生理作用。猫胃饥饿素的主要活性形式是一种在丝氨酸3位被辛酰化（C8:0）的28个氨基酸的肽；除了一个氨基酸残基替换外，该结构与大鼠和人胃饥饿素的结构相同。然而，在猫胃饥饿素中观察到肽长度和脂肪酸修饰存在很大的结构差异：发现了由缺少谷氨酰胺14和/或精氨酸28的27或26个氨基酸组成的肽，并且第三个丝氨酸残基被辛酸（C8:0）、癸酸（10:0）或不饱和脂肪酸（C8:1、C10:1和C10:2）修饰。与结构差异一致，分离出了两种不同长度的cDNA。给予合成的大鼠胃饥饿素可提高猫的血浆生长激素水平，其效力与大鼠或人类相似。禁食后猫的胃饥饿素血浆水平增加约2.5倍。本研究表明猫胃饥饿素存在结构差异，并提示与其他动物一样，胃饥饿素可能在猫的生长激素释放和进食中起重要作用。
