Ahmad S N, Alam S Q, Alam B S
Department of Biochemistry and Molecular Biology, Louisiana State University Medical Center, New Orleans 70119.
Cell Signal. 1990;2(1):29-41. doi: 10.1016/0898-6568(90)90030-e.
We have previously shown the incorporation of dietary omega-3 and omega-6 fatty acids from menhaden oil and corn oil, respectively, into membrane phospholipids of submandibular salivary gland (SMSG) of rat [Alam S. Q. and Alam B. S. (1988) Arch. Oral Biol. 33, 295-299]. We now demonstrate the influence of such incorporation on the regulation of G proteins and adenylate cyclase activity. Cholera toxin ribosylated three protein peptides (Mr 42,000, 44,000 and 46,000) to different extents in the two groups. We found 4.9- and 2.6-fold higher and 0.4-fold lower ribosylation of Mr 42,000, 44,000 and 46,000 peptides, respectively, in SMSG membranes of rats fed a diet containing 10% menhaden oil (group II) compared to those fed 10% corn oil (group I). Functional distinctions between different forms of these peptides are not known. Cholera toxin also exhibited radiolabelling of three peptides in the SMSG membranes from normal or fasting rats. In these membranes inhibitory G proteins were not detected by pertussis toxin dependent ADP ribosylation or by a low concentration of guanylyl 5-imidodiphosphate (10(-8) M), which selectively activates inhibitory G proteins which inhibit forskolin stimulated activity of adenylate cyclase. In group II membranes both basal and fluoride stimulated activities of adenylate cyclase were found to be significantly higher than the corresponding values in group I (P less than 0.02). In cholera toxin dependent ribosylated membranes of group I, basal and fluoride stimulated activities of adenylate cyclase were significantly higher than those obtained in the absence of cholera toxin (P less than 0.02). Surprisingly, corresponding values were found to be lower in ribosylated membranes of group II. This could be due either to conformational changes in heavily ribosylated G proteins, which alters coupling with the catalytic subunit of adenylate cyclase, or due to dissociation of excessive inhibitory beta gamma complex from alpha beta gamma complex upon the activation of G proteins.
我们之前已经表明，分别来自鲱鱼油和玉米油的膳食ω-3和ω-6脂肪酸可掺入大鼠下颌下唾液腺（SMSG）的膜磷脂中[阿拉姆·S·Q和阿拉姆·B·S（1988年）《口腔生物学文献》33卷，295 - 299页]。我们现在证明这种掺入对G蛋白调节和腺苷酸环化酶活性的影响。霍乱毒素对两组中的三种蛋白质肽段（分子量42,000、44,000和46,000）进行了不同程度的核糖基化。我们发现，与喂食10%玉米油的大鼠（第一组）相比，喂食含10%鲱鱼油饮食的大鼠（第二组）的SMSG膜中，分子量42,000、44,000和46,000肽段的核糖基化分别高出4.9倍和2.6倍，低0.4倍。这些肽段不同形式之间的功能差异尚不清楚。霍乱毒素在正常或禁食大鼠的SMSG膜中也显示出对三种肽段的放射性标记。在这些膜中，百日咳毒素依赖性ADP核糖基化或低浓度的鸟苷酰5 - 亚氨基二磷酸（10⁻⁸ M）均未检测到抑制性G蛋白，低浓度的鸟苷酰5 - 亚氨基二磷酸可选择性激活抑制腺苷酸环化酶福斯高林刺激活性的抑制性G蛋白。在第二组膜中，腺苷酸环化酶的基础活性和氟化物刺激活性均显著高于第一组的相应值（P < 0.02）。在第一组的霍乱毒素依赖性核糖基化膜中，腺苷酸环化酶的基础活性和氟化物刺激活性显著高于未加霍乱毒素时的值（P < 0.02）。令人惊讶的是，在第二组的核糖基化膜中相应的值较低。这可能是由于高度核糖基化的G蛋白发生构象变化，改变了与腺苷酸环化酶催化亚基的偶联，或者是由于G蛋白激活后过量的抑制性βγ复合物从αβγ复合物中解离所致。
