一氧化氮参与调节盐胁迫下脱落酸诱导的小麦幼苗叶片脯氨酸的累积

不同浓度(0.01～5.00mmol/L)的外源一氧化氮(NO)供体硝普钠(SNP)以浓度依赖性的性式诱导150mmol/LNaCl胁迫下小麦(Triticum aestivum L.cv.Yangmai 158)幼苗叶片脯氨酸的累积.其中0.1 mmol/L的SNP效果最明显,而结合采用NO清除剂c-PTIO和血红蛋白的处理均分别逆转了该效应.研究结果还发现:0.1 mmol/L SNP诱导的脯氨酸累积还可能有利于盐胁迫下小麦幼苗的保水性;0.1 mmol/L的SNP显著激活了内源ABA的合成,而结合血红蛋白的处理则证实,在外源ABA诱导脯氨酸累积的过程中NO可能作用于ABA信号分子的下游,但NO和ABA信号分子在此诱导反应中不存在累积效应.进一步研究脯氨酸合成和降解的酶促反应途径,发现外源NO处理前4天内可能主要是通过提高△'-吡咯啉-5-羧酸合成酶(P5CS)的活性来促进脯氨酸的合成,以后直至第8天主要是通过抑制脯氨酸脱氢酶(ProDH)的活性来抑制脯氨酸的降解;ABA对于P5CS和ProDH活性的调节能力弱于NO.此外,Ca2 在NO诱导的盐胁迫下小麦叶片脯氨酸累积的信号分子途径中起重要的介导作用.     

Proline Oxidase and Water Stress-induced Proline Accumulation in Spinach Leaves

Spinach (Spinacia oleracea L.) leaf discs accumulated free proline when exposed to polyethylene glycol solutions of water potential less than −10 bars. At −20 bars, the accumulation was 11 micromoles per gram original fresh weight in a 24-hour period.     

Proline metabolism in sepsis

Summary Sepsis is characterized by an abnormal increase in plasma proline (PRO) level, which tends to be related to the severity of disease. This study has been performed to assess the relationship between changes in plasma PRO and levels and doses of other amino acids (AA) in critically ill septic patients undergoing total parenteral nutrition (TPN).Sixteen septic patients receiving TPN were randomly divided into two groups: 8 patients (Group A) received TPN with a standard AA solution, and 8 patients (Group B) with a modified AA solution (isonitrogenous, branchedchain AA enriched, with unchanged PRO concentration). Serial determinations of plasma AA profiles and of other variables were performed in each patient for a total of 396 measurements. In Group A mean plasma PRO level was 372M/L; changes in PRO were tightly correlated with changes in the levels of most of the other AA, and the highest PRO levels characterized the more severely unbalanced septic metabolic profiles. In Group B, plasma levels of PRO and of the other AA (except glutamate, aspartate, taurine and the three branched-chain AA) decreased. The decrease in PRO level was well correlated with the increased branched-chain AA dose and with simultaneous decreases in plasma lactate and respiratory quotient. These changes could be related to a specific effect of branched-chain AA on septic metabolic derangement and on PRO metabolism, and to an improved balance between protein synthesis and catabolism.     

Proline in the Osmoregulation of Brevibacterium lactofermentum

Osmoregulation in Brevibacterium lactofermentum was studied. Proline was accumulated up to approximately 35mg/g dry cell weight in the cells of a wild strain of the bacterium grown under osmotic stress. The osmotic tolerance of a proline auxotroph mutant obtained from the bacterium was lower than that in the wild strain. The activity of pyrroline-5-carboxylate reductase, one of the enzymes in the proline biosynthetic pathway, increased about 3-fold when the cells of B. lactofermentum were grown under osmotic stress. These data indicated that proline is important in osmoregulation in the bacterium.     

Effects of the Proline Analog l-Thiazolidine-4-carboxylic Acid on Proline Metabolism

The effect of various proline analogs on proline oxidation in mitochondria isolated from etiolated barley (Hordeum vulgare) shoots was investigated. Of the analogs tested, only l-thiazolidine-4-carboxylic acid (T4C) was an effective inhibitor. T4C (1 millimolar) inhibited proline (10 millimolar) -dependent 0₂ uptake an average of 67%. T4C was also oxidized to some degree (12.9 nanoatoms oxygen per minute per milligram protein for 10 millimolar). The effect of T4C on the oxidation of other mitochondrial substrates was also tested. T4C inhibited ¹-pyrrolidine-5-carboxylic acid-dependent oxygen uptake slightly (13%), the oxidation of malate plus pyruvate even less (6%), and stimulated the oxidation of succinate (+11%), exogenous NADH (+19%), and citrate (+20%). Thus, inhibition by T4C in mitochondria is relatively specific to proline oxidation. T4C was found to inhibit proline dehydrogenase and not the transport of proline into the matrix.     

Inter-chain Proline: Proline Contacts Contribute to the Stability of the Triple Helical Conformation

Abstract

The triple helical conformation observed in the collagen group of proteins is related to the presence of large numbers of imino residues and is derived from the stereochemical properties of these residues. The triple helix is stabilized by increasing numbers of these residues. Hydrogen bonds are usually considered to be a major factor in the formation and stability of protein conformation, however, imino residues are not hydrogen bond donors. We have evaluated the role of these residues in stabilizing the triple helix by re-examining two X-ray based structures of the triple helical polypeptide (Pro-Pro- Gly)₁₀ using molecular mechanics calculations. The two minimized structures are comparable in energy and have helical parameters close to the starting values for each starting structure. Our studies suggest that clusters of close van der Waals contacts between proline residues in adjacent chains contribute significantly to the stability of the triple helix. Preliminary NMR studies support this concept. We propose that non-bonded interactions between proline residues may be a significant stabilizing force in the triple helix generated by (Pro-Pro-Gly)₁₀.     

Mycorrhizal-Mediated Lower Proline Accumulation in Poncirus trifoliata under Water Deficit Derives from the Integration of Inhibition of Proline Synthesis with Increase of Proline Degradation

Proline accumulation was often correlated with drought tolerance of plants infected by arbuscular mycorrhizal fungi (AMF), whereas lower proline in some AM plants including citrus was also found under drought stress and the relevant mechanisms have not been fully elaborated. In this study proline accumulation and activity of key enzymes relative to proline biosynthesis (▵¹-pyrroline-5-carboxylate synthetase, P5CS; ornithine-δ-aminotransferase, OAT) and degradation (proline dehydrogenase, ProDH) were determined in trifoliate orange (Poncirus trifoliata, a widely used citrus rootstock) inoculated with or without Funneliformis mosseae and under well-watered (WW) or water deficit (WD). AMF colonization significantly increased plant height, stem diameter, leaf number, root volume, biomass production of both leaves and roots and leaf relative water content, irrespectively of water status. Water deficit induced more tissue proline accumulation, in company with an increase of P5CS activity, but a decrease of OAT and ProDH activity, no matter whether under AM or no-AM. Compared with no-AM treatment, AM treatment resulted in lower proline concentration and content in leaf, root, and total plant under both WW and WD. The AMF colonization significantly decreased the activity of both P5CS and OAT in leaf, root, and total plant under WW and WD, except for an insignificant difference of root OAT under WD. The AMF inoculation also generally increased tissue ProDH activity under WW and WD. Plant proline content significantly positively correlated with plant P5CS activity, negatively with plant ProDH activity, but not with plant OAT activity. These results suggest that AM plants may suffer less from WD, thereby inducing lower proline accumulation, which derives from the integration of an inhibition of proline synthesis with an enhancement of proline degradation.     

Proline Metabolism in Tetrahymena1

SYNOPSIS. By the use of ¹⁴C-labeled substrates it has been shown in Tetrahymena that proline is rapidly and completely oxidized to carbon dioxide and glutamate (65–70%), plus small amounts of aspartate and alanine (20%), the remainder being incorporated into macromolecular cell components. In comparison, acetate, glucose and glutamate are oxidized to a lesser extent (55%, 37% and 16%, respectively). Glucose and acetate are extensively incorporated into cell components (53% and 36%, respectively), while glutamate remains in the medium (76%). Thus proline is a source of readily available energy.     

Proline kinks in transmembrane alpha-helices

Integral membrane proteins often contain proline residues in their presumably alpha-helical transmembrane segments. This is in marked contrast to globular proteins, where proline is rarely found inside alpha-helices. Proline residues cause kinks in helices, and, in addition to leaving the i-4 backbone carbonyl without its normal hydrogen bond donor, also sterically prevent the (i-3)-carbonyl-(i + l)-amide backbone hydrogen bond from forming. Here, some structural aspects of proline kinks in transmembrane helices are discussed on the basis of an analysis of Pro-kinked helices in the photosynthetic reaction center and bacteriorhodopsin, as well as results from an analysis of Pro-containing transmembrane segments identified in the NBRF Protein Sequence Databank.     

Proline 107 is a major determinant in maintaining the structure of the distal pocket and reactivity of the high-spin heme of MauG

The diheme enzyme MauG catalyzes a six-electron oxidation required for posttranslational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. Crystallographic studies had shown that Pro107, which resides in the distal pocket of the high-spin heme of MauG, changes conformation upon binding of CO or NO to the heme iron. In this study, Pro107 was converted to Cys, Val, and Ser by site-directed mutagenesis. The structures of each of these MauG mutant proteins in complex with preMADH were determined, as were their physical and catalytic properties. P107C MauG was inactive, and the crystal structure revealed that Cys107 had been oxidatively modified to a sulfinic acid. Mass spectrometry revealed that this modification was present prior to crystallization. P107V MauG exhibited spectroscopic and catalytic properties that were similar to those of wild-type MauG, but P107V MauG was more susceptible to oxidative damage. The P107S mutation caused a structural change that resulted in the five-coordinate high-spin heme being converted to a six-coordinate heme with a distal axial ligand provided by Glu113. EPR and resonance Raman spectroscopy revealed this heme remained high-spin but with greatly increased rhombicity as compared to that of the axial signal of wild-type MauG. P107S MauG was resistant to reduction by dithionite and reaction with H(2)O(2) and unable to catalyze TTQ biosynthesis. These results show that the presence of Pro107 is critical in maintaining the proper structure of the distal heme pocket of the high-spin heme of MauG, allowing exogenous ligands to bind and directing the reactivity of the heme-activated oxygen during catalysis, thus minimizing the oxidation of other residues of MauG.     

Proline uptake in Streptomyces clavuligerus

Streptomyces clavuligerus was able to accumulate proline intracellularly throughout a wide range of external proline concentrations. Kinetic analysis of proline uptake indicated that this phenomenon is mediated by two saturable systems. One of them was a high-affinity system (Km = 11 microM), with low uptake capacity and specific for proline. The second system had lower affinity for proline (Km = 10.2 mM), higher uptake capacity, and was inhibited by several amino acids. Proline was not required as an inducer of the systems, which were neither repressed nor inhibited by ammonium.     

Proline oxidase in cultured mammalian cells

We sought a cultured cell line with Proline Oxidase activity to study the regulation and physiologic role of the enzyme in mammalian tissues. Among the cell lines tested, only LLC-RK1 cells, derived from rabbit kidney, had significant Proline Oxidase activity; the Km for proline of the enzyme from these cells was similar to that for the liver enzyme. LLC cells, Proline Oxidase positive, were able to convert proline to CO2. In contrast, CHL cells, Proline Oxidase negative, did not have this capability. The presence of Proline Oxidase in LLC cells and the absence of the enzyme in fibroblasts suggest that Proline Oxidase may serve as a marker enzyme for distinguishing parenchymal kidney cells from fibroblasts in culture. Cells transformed by SV40 virus and cells transformed by methylcholanthrene had activities higher that the parent cell line, but this effect of transformation could not be generalized to all transformed cells. Finally, L-hydroxy proline at 100-fold greater concentration than substrate L-proline failed to decrease proline oxidation. This finding suggests distinct degradative enzymes for these two amino acids.