Adenyl Cyclase Activity in Cultivated Human Skin Fibroblasts

CYCLIC 3′,5′-AMP (cyclic AMP) is an important regulator of cellular processes^{1, 2}. In target cells, hormones stimulate adenyl cyclase, an enzyme which catalyses the conversion of ATP to cyclic AMP, which acts as a “second messenger” on either a membrane or an enzyme system and produces a specific physiological response. Hormonal stimulation of adenyl cyclase in several tissues has been documented².     

Adenyl Cyclase and the Differentiation of β-Adrenoreceptors

WE have studied the enzyme adenyl cyclase to extend the evidence that β-adrenoreceptors consist of at least two types, β-1 and β-2 (refs. 1-4.) Cyclic 3′,5′-AMP has been shown to be the intracellular mediator of the action of various hormones, including the catecholamines and it has been suggested that adenyl cyclase is an integral part of the β-adrenoreceptor^5,6. Thus adenyl cyclase preparations from certain tissues should differ in their responsiveness to β-adrenoreceptor agonists and antagonists in a manner analogous to the intact tissues. We have therefore examined the differential effects of some sympathomimetic amines and their antagonists on the activity of adenyl cyclase preparations from rat heart and lung.     

Localization of Nucleic Acid Synthesis in Root Meristems

Adenine-8-C1¹⁴ was supplied to roots of Vicia faba and Alliumascalonicum and its incorporation into DNA was studied fromautoradiographs of hydrolysed sections. These roots have a quiescentcentre to the meristem where the cells do not synthesize DNAand probably, therefore, play no part in the construction ofthe root. The boundary between the quiescent centre and thecentral cap initials is clearly denned and this suggests thatthere is as little cell interchange between the histogens asthere is in roots with visibly discrete histogens.     

Nuclear Proteins During the Onset of Cell Proliferation in Pea Root Meristems

The DNA: proteins ratio in nuclei of root meristems of pea (Pisumsativum L. cv. Lincoln) changed considerably during germinationas cells moved from a quiescent to an actively proliferatingstate with a higher protein content in nuclei of the latter.Electrophoretic patterns of nuclear proteins extracted at differenttimes of germination were used to examine qualitative changes.The various patterns presented a substantial similarity butthere were some proteins whose content increased or decreasedand others which disappeared or appeared during germination.The bulk of these variations occurred between 24 and 48 h ofgermination, suggesting that they might be correlated to thetransition from quiescence to the proliferating state. The patternof nuclear proteins obtained from adult differentiated roottissue was also examined. We tried to purify five differentnuclear protein components from intact nuclei by a multi-stepextraction procedure using a series of different buffers toascertain the nature of proteins presenting major interestingvariations. Most of these proteins purified with the nuclearsap or ribosomal components. Key words: Cell proliferation, electrophoresis, Pisum sativum L, root meristems     

Relationship Between the Membrane Envelope of Rhizobial Bacteroids and the Plasma Membrane of the Host Cell as Demonstrated by Histochemical Localization of Adenyl Cyclase

By using adenyl cyclase as a marker enzyme, the relationship between the membrane envelope of the bacteroids of rhizobia and the plasma membrane of the host cell was demonstrated histochemically. Electron-dense deposits were found on the outer surface of the plasma membrane of the host cell and on the inner surface of the membrane envelopes of the bacteroids, but not in vacuole membranes, endoplasmic reticula, Golgi apparatus, and mitochondrial membranes. The results suggest that the membrane envelopes of the bacteroids are closely related to the host plasma membrane, and that entry of the bacteroids into the cytoplasm is in a manner similar to endocytosis.     

Response of Leucocyte Adenyl Cyclase to Isoprenaline and Effect of Alpha-blocking Drugs in Extrinsic Bronchial Asthma

The finding by several workers that biochemical responses to catecholamines are diminished in asthmatic patients during periods of active asthma as compared to normal subjects has led to the recognition of the beta-adrenergic blockade phenomenon, a common accompaniment of extrinsic bronchial asthma. Using an intact cell method to measure leucocyte adenyl cyclase activity, we have been able to show that there is a noticeably reduced responsiveness of this enzyme system (which is now identified with beta-receptor function) to isoprenaline in the leucocytes of patients suffering from acute bronchial asthma, but that asthmatic patients in remission could not be distinguished from normal persons in this respect. Evidently the defective beta-receptor function may be associated with overactivity of the alpha-receptors in acute bronchial asthma, since the responsiveness to isoprenaline stimulation could be restored towards normal by concomitant treatment of the leucocytes of these patients with alpha-receptor blocking drugs such as phentolamine or thymoxamine. Ouabain, though somewhat less potent, also enhanced responsiveness to isoprenaline stimulation. The relation of these results to the clinical observation of adrenaline resistance in active asthma suggests that alpha-receptor blocking drugs may be of value in restoring the sensitivity of beta-receptors to sympathomimetic amines.     

热胁迫对豌豆下胚轴生理的一些影响

通过测定热驯和热胁迫下3个豌豆品种幼苗下胚轴生长、细胞膜损伤、抗坏血酸（AsA）和丙二醛（佃A）含量的变化及热激蛋白70（HSP70）表达,探讨热胁迫对豌豆生理的影响。结果表明,在48℃高温胁迫下豌豆种子萌发率下降,幼苗下胚轴生长受抑制,细胞膜受损,AsA含量下降,MDA含量升高;经37℃热驯再48℃热激处理的下胚轴长度和ASA明显高于直接热胁迫的,细胞膜受损程度和MDA含量则低于后者。HSP70测定表明,除台湾品种外,37℃热驯1h不足以诱导HSP70表达;而37℃热驯后常温恢复再48℃热激和直接48℃热激均能诱导HSP70表达,其中蒙自品种经热驯后再热激的HSP70表达量高于直接热激的。     

Effects of Long-acting Thyroid Stimulator (LATS) and LATS Protector on Human Thyroid Adenyl Cyclase Activity

The long-acting thyroid stimulator (LATS) has been thought to be responsible for the hyperthyroidism of Graves''s disease. It is detected by its effect on the mouse thyroid gland but cannot be found in all patients with hyperthyroidism. In an attempt to clarify the problem of LATS-negative hyperthyroidism, serum was obtained from untreated patients and its effect in vitro on human thyroid tissue examined, using the activation of adenyl cyclase as a measure of stimulation. Human thyroid adenyl cyclase was activated by both thyroid-stimulating hormone (TSH) and LATS. Thyroid tissue obtained from patients with Graves''s disease was relatively less responsive to LATS than was non-toxic thyroid tissue. Of the 24 samples studied five contained LATS and all of these activated adenyl cyclase. The presence of LATS protector in LATS-negative hyperthyroid patients was confirmed but LATS-negative sera had no effect on human thyroid adenyl cyclase activity.     

Cytochemical Localization of Guanylyl Cyclase Activity in Rabbit Taste Bud Cells

Guanylyl cyclase activity was cytochemically demonstrated inrabbit foliate taste buds. The enzymatic activity was localizedin the apical portion (microvilli and neck) of taste bud cells.Especially strong activity was observed on the microvillousmembrane of type I (dark) cells and often on a blunt processof type III cells. The microvilli of type II (light) cells showedweak enzymatic activity. Considering that the apical portionof taste cells is a likely site of interaction between tastestimuli and the cells, the results support the idea that cyclicGMP is involved in taste transduction.     

Genetic Characterization of Mutations Which Affect Catabolite-Sensitive Operons in Escherichia coli, Including Deletions of the Gene for Adenyl Cyclase

Sixty-two spontaneous mutations have been characterized which reduce the level of expression of catabolite-sensitive operons. These mutations appear to affect either the crp (catabolite gene activator protein) or cya (adenyl cyclase) loci. No new loci have been discovered. Deletions of the cya gene do not remove an essential function. phi80 transducing phage for the cya gene have been used to do recombination and complementation studies on cya mutants.     

Neurohormones on Brain Adenyl Cyclase Activity <Emphasis Type="Italic">in vivo</Emphasis>

CYCLIC adenosine 3′,5′-monophosphate (cyclic AMP) has been suggested to be the receptor site for neurotransmitters as well as a second messenger which mediates the action of a variety of hormones and neurohormones in animals and human tissues. Cyclic AMP is derived from adenosine triphosphate (ATP) by the activity of adenyl cyclase and it is metabolized into adenosine monophosphate (AMP) by phosphodiesterase. Beta receptor and adenyl cyclase may be the same in the peripheral tissues¹. In vitro activation of adenyl cyclase activity by various putative neurotransmitters such as noradrenaline (NA), 5-hydroxytryptamine (5-HT), acetylcholine (ACh) and histamine in preparations from brain homogenates and slices is well established². The in vivo effect, however, of these neurohormones on adenyl cyclase has not been studied.     

Subcellular Localization of Adenylate Cyclase in the Shoot Apices of Bryum argenteum Hedw

Adenylate cyclase activity has been detected in the shoot apicesof Bryum argenteum at the ultrastructural level, using adenylylimidodiphosphate as substrate. Heavy deposits of the reactionproduct were observed along the plasma membrane, tonoplast andthe membranous system of developing plastids. No clear stainingwas associated with other subcellular membranes. Mosses, adenylate cyclase, Bryum, cyclic AMP     

硫霉素环化酶基因在变铅青链霉菌TK24中的表达及基因定位

将含有硫霉素环化酶基因的重组质粒p6BCl2转化变铅青链霉菌(Streptomyceslividans)TK24,含有p6BCl2的转化子细胞抽提液分别与琉霉素生物合成阻断变株Y,发酵液以及纯化的Y。中间产物经过体外共培养可产生活性物质．化学分析表明与Y,发酵液混合后产生的是硫霉素,与纯化的Y。中间产物混合产生的是一种不稳定的活性物质。说明硫霉素环化酶基因在S.lividans TK24中得到了表达,其产物以Y。中间产物为底物并弥补了Y,中的缺陷。对p6Bcl2中4．5kb外源片段进行了限制酶酶切分析,建立了酶切图谱．利用含硫霉素环化酶基因的S．Lividans TK24转化子体外转化Y,的应用体系,将硫霉素环化酶基因定位在0．9kb Hinc I—Pst I片段上,并证明了硫霉紊环化酶的活性与IPNS同源片段无关。以上实验为进一步研究琉霉素环化酶基因的结构打下了基础。     

Stimulation of Adenyl Cyclase by <Emphasis Type="Italic">Escherichia coli</Emphasis> Enterotoxin

THE acute diarrhoea of cholera is caused by an enterotoxin produced by Vibrio cholerae¹. Experimentally, the activity of this enterotoxin can be demonstrated in the ligated ileal loop of rabbits and dogs^2–4. In response to intraluminal application of cholera enterotoxin, these loops demonstrate net secretion of fluid and electrolytes⁵. V. cholerae, however, is not the only enteropathogen associated with acute diarrhoea. Certain strains of Escherichia coli, an organism usually considered to be normal bowel flora, have been associated with epidemics of acute diarrhoea in infants⁶, adults⁷ and a variety of animal species⁸. Like cholera, E. coli diarrhoea is the result of accidental introduction and colonization of the small intestine by an offending organism capable of producing an enterotoxin⁷.     

Nutrient Sensing in Plant Meristems

Plants need nutrient to grow and plant cells need nutrient to divide. The meristems are the factories and cells that are left behind will expand and differentiate. However, meristems are not simple homogenous entities; cells in different parts of the meristem do different things. Positional cues operate that can fate cells into different tissue domains. However, founder/stem cells persist in specific locations within the meristem e.g. the quiescent centre of root apical meristem (RAM) and the lower half of the central zone of the shoot apical meristem (SAM). Given the complexity of meristems, do their cells simply respond to a diffusing gradient of photosynthate? This in turn begs the question, why do stem cell populations tend to have longer cell cycles than their immediate descendants given that like all other cells they are directly in the path of diffusing nutrient? In this review, we have examined the extent to which nutrient sensing might be operating in meristems. The scene is set for sugar sensing, the plant cell cycle, SAMs and RAMs. Special emphasis is given to the metabolic regulator, SnRK1 (SNF1-related protein kinase 1), hexokinase and the trehalose pathway in relation to sugar sensing. The unique plant cell cycle gene, cylin-dependent kinase B1;1 may have evolved to be particularly responsive to sugar signalling pathways. Also, the homeobox gene, STIMPY, emerges strongly as a link between sugar sensing, plant cell proliferation and development. Flowering can be influenced by sucrose and glucose levels and both meristem identity and organ identity genes could well be differentially sensitive to sucrose and glucose signals. We also describe how meristems deal with extra photosynthate as a result of exposure to elevated CO₂. What we review are numerous instances of how developmental processes can be affected by sugars/nutrients. However, given the scarcity of knowledge we are unable to provide uncontested links between nutrient sensing and specific activities in meristems.     

The Initiation and Development of Lateral Meristems in the Pea Root: II. THE EFFECT OF INDOLE-3-ACETIC ACID

The results of the first paper in this series (Pecket, 1957)indicated that lateral root initiation in isolated pea rootsdepends upon an apically moving factor or complex of factorsprovided by the mature tissue of the root. The present investigationanalyses the effect of externally applied IAA on lateral rootformation and uses the methods employed in the earlier work.Observations made on roots in which three regions have beendistinguished show that increasing IAA concentration does notcause similar changes in all pans of the root, nor does it causeidentical effects on primordium initiation and on the subsequentemergence of the initials as lateral roots. The latter factexplains why the emphasis in the present work has been laidon initiation rather than on emergence. The results of experimentsare reported in which two variables are involved, IAA concentrationand the presence or absence of the two terminal regions of theroot. These results are considered to support the conclusionsof the earlier paper. It is suggested that the stimulant movingfrom mature tissue is not IAA itself but that the productionof the stimulant may be increased when IAA is supplied. A gradientof reaction to the stimulant appears to exist in the root, reactionbeing maximal in the mature tissue.     

Activities of Adenylate Cyclase and Changes in cAMP Concentration in Root Cells of Pea Seedlings Infected with Mutualists and Phytopathogens

Work was carried out on pea (Pisum sativum L.) seedling roots to assess the attachment of the nitrogen-fixing symbiotic bacteria Rhizobium leguminosarum bv. vicea (Rlv) and the bacterial phytopathogens—specific Pseudomonas syringae pv. pisi (Psp) and nonspecific Clavibacter michiganensis ssp. sepedonicus (Cms). Different root zones were examined: (I) the meristem, 2 mm from the root tip; (II) the root hair-free zone, 27 mm; (III) the zone of root hair anlages, 712 mm; (IV) the young root hair zone, 1217 mm; and (V) the zone of root hair that completed the growth, 1722 mm. It was found earlier that the zones differed in their susceptibility to Rlv. In the present work, reactions of particular components of the adenylate cyclase signaling system (ACSS) were estimated, i.e., concentration of cAMP and activities of transmembrane adenylate cyclase (tAC) and soluble adenylate cyclase (sAC) in these zones after different times post inoculation (5, 15, 120, and 360 min). It was revealed that the degree of activation of particular components of ACSS did not depend on the sorption rate of differently specialized bacteria. Upon contact with Rlv, the character of changes in tAC and sAC activities was almost the same in different root zones and resembled the dynamics of the cAMP content. Inoculation with Psp changed the cAMP level similarly to that with Rlv, but the dynamics of tAC and sAC was opposite to each other in most cases. Inoculation with Cms, in spite of the absence of its attachment, elevated the cAMP content and activated tAC and sAC. It is suggested that the above-mentioned changes in ACSS is associated with exometabolites of Rlv, Psp, and Cms, which activate the PAMP-induced immunity of the pea seedling cells. The uniform dynamics of cAMP in different root zones upon the exposure to Rlv and Psp seems to reflect the specific reaction and, presumably, fulfills different functions—regulatory with Rlv and defensive with Psp. Upon short-term contact with Cms, the cAMP dynamics in the same root zones displayed a nonspecific character that might be related to the rate of adsorption of exopolysaccharides by the root hair. The systemic response of ACSS was observed in the hypocotyls of the seedlings exposed to any of the three organisms.