Cripps M M, Bennett D J
Department of Physiology, Louisiana State University Medical Center, New Orleans.
Life Sci. 1992;50(5):PL19-24. doi: 10.1016/0024-3205(92)90442-r.
The mechanism by which the inhibitory effect of d-ala2-met-enkephalinamide (DALA) on lacrimal acinar adenylyl cyclase is exerted was assessed in membrane preparations by a cAMP protein binding assay. Inhibition by the analogue was GTP-dependent with a significant enhancement of the inhibitory effect by GTP. While pretreatment of membranes with either cholera or pertussis toxin resulted in stimulation of adenylyl cyclase activity, modification of the Gi alpha subunit by pertussis-toxin catalyzed ADP-ribosylation did not effect the hormonal inhibition of adenylyl cyclase. Incubation of membranes with manganese, however, prevented the inhibitory action of DALA in addition to enhancing basal and forskolin-stimulated adenylyl cyclase activity. The results suggest that the inhibitory effect of DALA in lacrimal acinar cells is exerted via a mechanism other than pertussis-toxin sensitive coupling of the receptor to adenylyl cyclase through Gi. The mechanism may be effected through a pertussis-toxin insensitive G protein, through an interaction with Gi that is pertussis-toxin insensitive, or through an interaction with the catalytic subunit of adenylyl cyclase.
通过cAMP蛋白结合试验在膜制剂中评估了d-丙氨酸2-甲硫氨酸脑啡肽酰胺（DALA）对泪腺腺泡腺苷酸环化酶抑制作用的机制。该类似物的抑制作用是GTP依赖性的，GTP可显著增强其抑制作用。虽然用霍乱毒素或百日咳毒素预处理膜可刺激腺苷酸环化酶活性，但百日咳毒素催化的ADP-核糖基化对Giα亚基的修饰并不影响激素对腺苷酸环化酶的抑制作用。然而，用锰孵育膜除了增强基础和福斯高林刺激的腺苷酸环化酶活性外，还可阻止DALA的抑制作用。结果表明，DALA在泪腺腺泡细胞中的抑制作用是通过一种不同于百日咳毒素敏感的受体与腺苷酸环化酶通过Gi偶联的机制发挥的。该机制可能通过对百日咳毒素不敏感的G蛋白、通过与对百日咳毒素不敏感的Gi相互作用或通过与腺苷酸环化酶催化亚基的相互作用来实现。
