Valentincic T, Metelko J, Ota D, Pirc V, Blejec A
Department of Biology, University of Ljubljana. National Institute of Biology, Vecna pot 111, 1000 Ljubljana, Slovenia.
Chem Senses. 2000 Feb;25(1):21-9. doi: 10.1093/chemse/25.1.21.
Olfactory discrimination of amino acids was investigated in brown bullhead catfish (Ameiurus nebulosus). Based on the magnitude of the observed food search activity of catfish conditioned to single amino acids, the tested compounds were classified as being detected by the catfish as equal to, similar to, or different from the conditioned stimulus. L-Proline (L-Pro)-conditioned brown bullhead catfish discriminated all amino acids from L-Pro, but catfish conditioned to L-valine (L-Val) and L-isoleucine (L-Ile) did not discriminate L-Val from L-Ile nor L-Ile from L-Val; however, all other amino acids tested were always discriminated from these two compounds. Catfish conditioned to L-alanine (L-Ala) discriminated basic, acidic and several neutral amino acids with long side-chains (LCNs) from L-Ala; however, they did not always discriminate L-Ala from all neutral amino acids with short side-chains (SCNs). The L-norleucine (L-nLeu)-conditioned fish responded to L-norvaline (L-nVal), L-methionine (L-Met) and L-Ala similarly to L-nLeu, indicating that these amino acids are detected as similar or identical to L-nLeu. L-nLeu was, however, discriminated from L-Ala in L-Ala-conditioned catfish. Interestingly, L-leucine (L-Leu) was discriminated from the conditioned stimuli, L-Ala, L-Ile and L-Val, indicating independent receptors for L-Leu. Although conditioned catfish discriminated other amino acids from L-arginine hydrochloride (L-Arg), in some tests they were unable to discriminate L-Arg from L-lysine hydrochloride (L-Lys). These results imply the existence of independent olfactory receptive pathways for: (i) L-Pro; (ii) basic amino acids (L-Arg and L-Lys); (iii) L-Leu; (iv) other neutral amino acids with branched side-chains (L-Ile and L-Val); (v) neutral amino acids with long linear side-chains (L-nLeu, L-nVal and L-Met); (vi) neutral amino acids with short side-chains; and (vii) amino acids with sulfhydryl groups (L-Cys and L-homoCys).
对褐首鲶（Ameiurus nebulosus）的氨基酸嗅觉辨别能力进行了研究。根据对单一氨基酸进行条件训练的鲶鱼所观察到的食物搜索活动的强度，将测试化合物分类为鲶鱼检测到的与条件刺激物相等、相似或不同的物质。用L-脯氨酸（L-Pro）进行条件训练的褐首鲶能区分所有氨基酸与L-Pro，但用L-缬氨酸（L-Val）和L-异亮氨酸（L-Ile）进行条件训练的鲶鱼无法区分L-Val与L-Ile，也无法区分L-Ile与L-Val；然而，所有其他测试的氨基酸总能与这两种化合物区分开来。用L-丙氨酸（L-Ala）进行条件训练的鲶鱼能区分碱性、酸性和几种带有长侧链（LCNs）的中性氨基酸与L-Ala；然而，它们并不总能区分L-Ala与所有带有短侧链（SCNs）的中性氨基酸。用L-正亮氨酸（L-nLeu）进行条件训练的鱼对L-正缬氨酸（L-nVal）、L-甲硫氨酸（L-Met）和L-Ala的反应与对L-nLeu的反应相似，表明这些氨基酸被检测为与L-nLeu相似或相同。然而，在L-Ala条件训练的鲶鱼中，L-nLeu与L-Ala能被区分开来。有趣的是，L-亮氨酸（L-Leu）能与条件刺激物L-Ala、L-Ile和L-Val区分开来，表明存在L-Leu的独立受体。尽管经过条件训练的鲶鱼能区分其他氨基酸与盐酸L-精氨酸（L-Arg），但在某些测试中，它们无法区分L-Arg与盐酸L-赖氨酸（L-Lys）。这些结果表明存在独立的嗅觉感受通路用于：（i）L-Pro；（ii）碱性氨基酸（L-Arg和L-Lys）；（iii）L-Leu；（iv）其他带有支链侧链的中性氨基酸（L-Ile和L-Val）；（v）带有长线性侧链的中性氨基酸（L-nLeu、L-nVal和L-Met）；（vi）带有短侧链的中性氨基酸；以及（vii）带有巯基的氨基酸（L-Cys和L-高半胱氨酸）。
