Stimulation of proliferation ofTetrahymena pyriformis by trace rare earths

Using two Chinese strains ofTetrahymena pyriformis, S1 and BJ4, as the biological models, the effects of lighter rare earths (lanthanum, cerium, praseodymium, neodymium, samarium, and europium), representatives of heavier rare earths (yttrium and thulium), and mixed rare earths were studied. The stimulation of population growth ofTetrahymena in peptone-glucose media containing trace amounts of these elements have been observed. The mechanisms for the beneficial effects of rare earth elements in low concentrations remains to be discovered.     

The biological relevance of HPLC-purified vasoactive intestinal polypeptide monoiodinated at tyrosine 10 or tyrosine 22

Three major forms of monoiodinated VIP (M125I-VIP) were isolated after chloramine-T iodination and HPLC purification. The iodinated tyrosine residue was located in each form of M125I-VIP using arginase C and trypsin digestion for obtaining defined fragments containing only one tyrosine residue. The HPLC isolated iodinated fragments thus obtained were used for HPLC comigration studies with iodinated synthetic C and N terminal VIP fragments and for amino acid analysis. The first two eluting peaks 1 and 2 are (M125I-Tyr10-VIP); peak 1 has an oxidized methionine; peak 3 is a (M125I-Tyr22-VIP) which also has an oxidized methionine. A reduced counterpart of peak 3 named peak 4 was isolated by further HPLC analysis. The ability of the different species of M125I-VIP to stimulate adenosine cyclic 3',5'-phosphate (cAMP) production in transformed colonic cells in culture (HT-29) was compared to that of native VIP. The mean potencies of the M125I-VIP species expressed as a percentage relative to the potency of native VIP were, peak (1): 0.98; (2): 0.84; (3): 1.38; (4): 1.48, in the range of concentrations tested (2-60 pM). The M125I-Tyr22-VIP are significantly more active than native VIP (P less than 0.01). Oxidation of methionine or iodination of tyrosine 10 does not significantly modify the biological activity of VIP. We conclude that iodination of Tyr-22 located in the apolar helical COOH-terminal of VIP increases the effectiveness of VIP interaction with its receptors. Thus the tyrosyl residue and the localized hydrophobic features of VIP are critically involved in the function of this neurotransmitter.     

Metabolic relationship between arachidonate activation and its transfer to lysophospholipids by brain microsomes

Evidence is presented to indicate a metabolic relationship between arachidonic acid activation and its transfer to lysophospholipds by brain microsomes. Thus, in the presence of 1-acylglycerophosphocholines or 1-acyl-glycerophosphoinositols, the activation of labeled arachidonate to its acyl-CoA was enhanced, and the acyl-CoA formed was, in turn, transferred to the lysophospholipids to form the respective diacyl-glycerophospholipids. The coupling effect seems to pertain mainly to the lysophospholipids which are good substrates of the acyltransferase. Other lyso-compounds were either not effective or inhibitory to the arachidonate activation process. The activation-transfer activity mediated by the fatty acid ligase and acyltransferase could be dissociated by Triton X-100, which apparently stimulated the acyl-CoA ligase activity but inhibited the acyltransferase. These results suggest that fatty acid ligase and acyltransferase are located in close proximity within the membrane domain. The existence of a close metabolic relationship between these two enzymic reactions is important for maintaining a dynamic equilibrium between the free fatty acids and the membrane phospholipids. The mechanism is also useful in regulating the cellular acyl-CoA and lysophospholipid metabolism, because both compounds have membrane perturbing properties when present in excessive quantity.     

植物磷酸烯醇式丙酮酸羧化酶的可逆胍变性

纯化的高梁叶片磷酸烯醇式丙酮酸羧化酶(PEP羧化酶)经不同浓度的盐酸胍处理变性失活后,在试验的蛋白浓度范围内,它的失活时间进程的动力学分析表明为一级反应。0.4 M盐酸胍处理25分钟后(O℃),酶的催化活性完全丧失,酶蛋白的远紫外圆二色性光谱、内源荧光光谱及免疫特异性等测定均表明酶的结构发生了深刻变化。甘油及PEP羧化酶的变构效应剂G6P和甘氨酸对酶在盐酸胍溶液中的变性作用有一定的保护效果。变性酶用复性缓冲液稀释20倍后,在最佳条件下,再经30分钟保温,酶的催化活性能恢复70％以上。G6P和甘氨酸能促进变性酶的复性,甘油亦有明显效果。随着酶活性的恢复,它的远紫外圆二色性、内源荧光及免疫特异性也随之恢复,变性酶的复性速率在常温下(25℃)比在低温下(0℃)要快得多。     

水稻胚胎形成期间蛋白质和RNA合成活力的变化

用~3H-亮氨酸和~3H-尿苷标记不同发育时期的稻胚,发现蛋白质合成活力呈四阶段变化;各种RNA的合成与胚胎各发育阶段密切有关。α-鹅膏蕈碱(1.0μg/ml)对稻胚RNA合成的抑制作用在开花后7、15和18天较强,13天时很弱。在水稻胚胎形成期间,胚细胞蛋白质合成活力高峰先后出现于胚分化后期(开花后11天)和成熟中期(18天);mRNA的合成在分化初期(7天)和成熟中期(15～18天)较强;而rRNA和/或tRNA的合成高峰则出现在胚胎器官原基分化已经完成时(13天)。     

Defective hepatic lipoprotein receptor binding of beta-very low density lipoproteins from type III hyperlipoproteinemic patients. Importance of apolipoprotein E

Apolipoprotein (apo-) E2 and beta-migrating very low density lipoproteins (beta-VLDL) (which were isolated from type III hyperlipoproteinemic subjects) both demonstrated defective binding to apo-E and apo-B,E receptors on dog liver membranes and to apo-B,E low density lipoproteins (LDL) receptors on fibroblasts. The defective binding activity of the apo-E2 and beta-VLDL varied from very poor to nearly normal. The ability of the beta-VLDL to interact with hepatic apo-E receptors was enhanced by the addition of normal apo-E3 to the beta-VLDL. Furthermore, cysteamine treatment of the apo-E2 in beta-VLDL enhanced binding of the beta-VLDL to both apo-E and apo-B,E receptors. The importance of apo-E in mediating the receptor binding of beta-VLDL to these receptors was confirmed by using monoclonal antibodies. The residual binding activity of beta-VLDL to apo-E and apo-B,E receptors was inhibited by greater than 90% with anti-apo-E, while the addition of anti-apo-B had little effect. The apo-B in the beta-VLDL was capable of binding to apo-B,E receptors after the hydrolysis of the beta-VLDL triglycerides with milk lipoprotein lipase. Lipase treatment yielded, two subfractions of beta-VLDL. One fraction (d = 1.02 to 1.03 g/ml) was enriched with apo-B100; the other fraction (d less than 1.006 g/ml) was enriched with apo-B48 and apo-E2. Significantly increased amounts of the apo-B100-enriched fraction bound to apo-B,E receptors. Inhibition of this binding caused by the addition of anti-apo-B indicated that the binding activity of this subfraction was mediated by apo-B100. The apo-B48-enriched fraction did not show a significant increase in receptor binding, suggesting that apo-B48 does not bind to these receptors. In a control experiment, it was shown that triglyceride-rich VLDL, which contain normal apo-E3 and apo-B100, bind significantly to both liver apo-E receptors and fibroblast apo-B,E receptors. This binding activity was inhibited by greater than 90% with anti-apo-E. Lipase hydrolysis of the VLDL did not further enhance their receptor-binding activity. These results demonstrate that apo-E, and not apo-B, is the major determinant mediating the receptor-binding activity of cholesterol-rich beta-VLDL and triglyceride-rich VLDL.     

Age-related and diurnal changes in Met5-Enk-Arg6-Phe7 and Met5-enkephalin contents of pituitary and rat brain structures

The beta-endorphin, met5-enkephalin-arg6-phe7 (MEAP) and met5-enkephalin (ME) changes related to age and diurnal rhythms were studied in various regions of rat brain and in the pituitary by specific radioimmunoassays. The contents of MEAP, met5-enkephalin and beta-endorphin were higher in the pituitary of old rats (18 months old) than that of young rats (23 days old) while the content of these opioid peptides was higher in the hypothalamus of young rats than in that of old rats. Beta-endorphin was also higher in the striatum of 23 days old rats, but no age-associated changes were observed in the hippocampus, brain stem or cortex. In the diurnal rhythm study, it was found that in the hypothalamus and striatum of the adult rat (2-3 months old), both MEAP and ME contents were higher at mid-dark than at mid-light and that in the intermediate posterior lobe of the pituitary, the ME content was also higher at mid-dark.     

Temperature-sensitive high affinity [3H]serotonin binding: Characterization and effects of antidepressant treatment

Characterization of temperature-sensitive [³H]serotonin (5-HT) binding sites (1 and 4 nM Kd sites) revealed complex inhibition by neuroleptics and serotonin antagonists. There was no simple correlation with affinities for S₁ and S₂ receptors. $\text{In vivo}$ pretreatment (48 h before) with mianserin did not alter Bmax or Kd for the 1 nM Kd [³H]5-HT site, although [³H]ketanserin (S₂) densities were decreased by 50%. This suggested that possible S₂ components of [³H]5-HT binding must be negligeable, even though ketanserin competed with high affinity (IC₅₀ = 3 nM) for a portion of the 1 nM Kd [³H]5-HT site. Low concentrations of mianserin inhibited the 1 nM Kd [³H]5-HT site in a non-competitive manner, as shown by a decrease in Bmax with no change in Kd after $\text{in vitro}$ incubation. The complex inhibition data may therefore represent indirect interactions through another site.     

南瓜雌蕊与自花及远缘花粉的相互作用

南瓜柱头表面经去垢剂、蛋白酶及Con A处理后花粉不能萌发或花粉管生长受阻,Con A能专一地与柱头表面结合。柱头块加入培养液可促进花粉萌发。不同的远缘花粉授粉后在雌蕊不同部位受阻。在成熟南瓜雌蕊提取液中检测到血凝活性,凝集素可能参与雌蕊对远缘花粉的抑制。