Poly(A)⁺ RNA encoding proteins capable of transporting L-methionine and/or DL-2-hydroxy-4-(methylthio) butanoic acid are present in the intestinal mucosa of broilers

To investigate the presence of poly(A)⁺ RNA that encode proteins capable of transporting L-methionine (L-Met) and/or DL-2-hydroxy-4-(methylthio) butanoic acid (HMB), Xenopus oocytes were injected with poly(A)⁺ RNA isolated from broiler intestinal mucosa. Healthy oocytes at stage V or VI were collected from Xenopus laevis and microinjected with water, poly(A)⁺ RNA or size-fractioned poly(A)⁺ RNA. The ability of the injected oocytes to take up either L-Met or HMB was examined by incubating oocytes with [methyl-³H]-L-Met or [5-¹⁴C]-HMB. A greater uptake of L-Met (P < 0.01) and HMB (P < 0.05) by oocytes injected with poly(A)⁺ RNA from the duodenum, jejunum and ileum of the small intestine was observed compared with water-injected oocytes. The greatest (P < 0.05) uptake occurred when poly(A)⁺ RNA from the jejunum or ileum was injected. Injections from four different pools of sucrose gradient-fractionated poly(A)⁺ RNA from all three intestinal segments induced (P < 0.01) L-Met uptake. There were three to four different pools of sucrose gradient-fractionated poly(A)⁺ RNA from the duodenum, jejunum and ileum that induced (P < 0.05) HMB uptake. Uptake of HMB was greater at pH 5.5 than at pH 7.5 and was independent of Na⁺. Uptake of L-Met induced by all four poly(A)⁺ RNA pools decreased dramatically when Na⁺ was removed from the uptake buffer, which indicated that the majority of L-Met uptake was Na⁺-dependent. These results indicate that there are multiple sized poly(A)⁺ RNA that encode proteins capable of mediated transport of L-Met and/or HMB present in broiler intestinal mucosa.