Role of Complement C5a/C3a agonists existing broadly in animals and plants

补体C3a从补体C3的氨基端区释放，引起平滑肌的炎症和收缩。我们发现补体C3a具有抗镇痛和抗健忘症等中枢作用。从酪蛋白、大米白蛋白、血红蛋白、血清白蛋白和组蛋白的胰蛋白酶消化液中分离到的低分子量C3a激动剂在其羧基端、疏水残基- x_1 - leu - x_2 - arg上具有共同的序列。这些肽可能与C3a受体结合，因为其序列与C3a的羧基端相同。在一些内源性生物活性肽的一级结构中发现了类似的肽。这类多肽不仅广泛存在于动物中，也广泛存在于植物中，因此只有一部分可能具有生理意义。补体C5a也从补体C5的氨基端区释放，具有与C3a相同的强大生物活性。从猪血清白蛋白中释放的白蛋白A （ala - ph - lys - ala - trp - ser - leu - ala - arg）可结合C3a和C5a受体。另一方面，乳铁蛋白释放的ph - lys - asp - cys - his - leu - ala - arg与C5a受体结合。由于C5a的羧基末端结构为Lys- asp - met - gln - leu - gly - arg，因此在羧基末端的第7个残基上的Lys似乎对C5a受体的亲和力至关重要。因此，C3a和C5a激动剂广泛存在于动物和植物中。其中一些有望用作药品或食品，以改善我们的健康。

Complement C3a which is released from the amino-terminus region of Complement C3 induces inflammation and contraction of smooth muscle. We found that Complement C3a shows central effects such as anti-analgesia and anti-amnesia. Low molecular weight C3a agonists we isolated from tryptic digests of casein, rice albumin, hemoglobin, serum albumin and histone have common sequence at their carboxyl termini, hydrophobic residue-X_1-Leu-X_2-Arg. These peptides might bind C3a receptor because the sequence is common to that at the carboxyl terminus of C3a. Similar peptides were found in the primary structure of some endogenous bioactive peptides. Only a part of such peptides might have' physiological significance because such peptides are found broadly not only in animals but also in plants.Complement C5a which is also released from the amino-terminus region of Complement C5 has potent biological activities common to those of C3a. Albutensin A, Ala-Phe-Lys-Ala-Trp-Ser-Leu-Ala-Arg, which is released from porcine serum albumin binds both C3a and C5a receptors. On the other hand, Phe-Lys-Asp-Cys-His-Leu-Ala-Arg, which is released from lactoferrin binds C5a receptor. The Lys at the 7th residue from the carboxyl terminus seems to be essential for C5a receptor affinity since the structure at the carboxyl terminus of C5a is Lys-Asp-Met-Gln-Leu-Gly-Arg. Thus, C3a and C5a agonists existing broadly in animal and plants. It is expected to use some of them as pharmaceutical drugs or foods to improve our health.