Microbial sensor for aspartame

Summary A microbial amperometric sensor using immobilized Bacillus subtilis cells was developed for the determination of the dipeptide sweetener aspartame (l-aspartyl-l-phenylalaninemethylester). From 0.07 to 0.6 mmol/l aspartame, a linear dependence of the initial current change (i.e., change in respiration rate) was obtained. The sensitivity for aspartame was one order of magnitude higher than for its amino acid constituents. The microbial sensor was stable for 8 weeks.     

合成阿斯巴甜菌种的筛选

为了探索酶法合成阿斯巴甜的新思路和新方法,从富含蛋白的土样中筛选出能够分解二肽阿斯巴甜的菌种。利用其可逆性的特点,以L-天门冬氨酸和L-苯丙氨酸甲酯为主要合成原料,以菌体酶作为催化剂进行合成实验。经高效液相色谱检测,结果表明筛选到一株菌(ASPD1)能够合成阿斯巴甜;通过单因素实验法探讨了反应时间、温度、pH值等诸因素对产物形成的影响。     

构型与构象

构型和构象是表征分子结构特征的易混淆的两个概念,构型是指具有一定构造的分子中原子或基团的固有空间排列。广义的构象是指分子中原子或基团在三维空间的取向和定位,狭义的构象是指具有相同构造和构型分子中原子或基团在空间的取向和定位。构型和构象既相互区别,又相互联系。对分子构型和构象概念的正确认识是阐明生物大分子结构与功能复杂关系的重要前提,对其正确地理解和运用将有助于教师教学任务的完成和学生对相关知识的理解和掌握。     

Acute effects of aspartame on aggression and neurochemistry of rats

The inverse relationship between serotonin and aggression was investigated in rats treated with aspartame, a sweetener thought to interfere with the synthesis of this neurotransmitter. Eleven adult, male Long-Evans rats received either aspartame (200-800 mg/kg, IP) or the vehicle prior to testing in a standard resident-intruder paradigm. Contrary to our hypothesis, aspartame significantly decreased aggression as shown by increased latencies to the first attack and decreased number of bites per session. Corresponding with the effects on aggression, aspartame significantly increased striatal levels of serotonin. It was concluded that high doses of aspartame reduced aggressive attack via a serotonergic mechanism while the lower dose was without effect on either variable.     

Comparison of thermochemistry of aspartame (artificial sweetener) and glucose

We have compared the gas phase thermochemical properties of aspartame (artificial sweetener) and α- and β-glucose. These parameters include metal ion affinities with Li⁺-, Na⁺-, K⁺-, Mg⁺²-, Ca⁺²-, Fe⁺²-, Zn⁺²-ions, and chloride ion affinity by using DFT calculations. For example, for aspartame, the affinity values for the above described metal ions are, respectively, 86.5, 63.2, 44.2, 255.4, 178.4, 235.4, and 300.4, and for β-glucose are 65.2, 47.3 32.9, 212.9, 140.2, 190.1, and 250.0 kcal mol⁻¹, respectively. The study shows differences between the intrinsic chemistry of aspartame and glucose.     

Aspartame and aspartame derivatives effect human thrombin catalytic activity

The study of small Asp-Phe analogs was undertaken since this dipeptide sequence is critical in fibrinogen recognition and catalysis. The inhibition of clotting activity by Asp-Phe-methyl ester (aspartame), formyl-Asp-Phe-methyl ester and acetyl-Asp-Phe was biphasic in all cases, indicating the presence of at least two binding sites. The N-terminally blocked derivatives are stronger inhibitors than aspartame. In contrast, tosyl-Gly-Pro-Arg-p'-nitroanilide hydrolysis was inhibited minimally by Asp-Phe-methyl, ester [Ki(app)=98 mM]. Acetyl-Asp-Phe inhibition of thrombin amidase activity was biphasic, tenfold stronger and appeared to be strongly cooperative. These results are discussed with respect to the inhibition of alpha-thrombin by ATP.     

A metabolite of aspartame inhibits angiotensin converting enzyme

Aspartame (L-aspartyl-L-phenylalanine methyl ester, is a widely used artificIal sweetener. In humans and other animals aspartame is initially hydrolyzed to L-aspartyl-L-phenylalanine by intestinal esterases. L-Aspartyl-L-phenylalanine inhibits angiotensin converting enzyme purified from rabbit lungs with a Ki of 11 +/- 2 microM, equipotent to the IC50 of 12 microM for 2-D-methyl-succinyl-L-proline which has been reported to be an orally active antihypertensive agent in rats. Thus the possibility exists that L-aspartyl-L-phenylalanine inhibits angiotensin converting enzyme in humans consuming large quantities of aspartame. Both aspartame itself and the diketopiperazine formed from it, 3-carboxymethyl-6-benzyl-2,5-diketopiperazine, are weak inhibitors with Ki's greater than 1 mM.     

Possible analgesic and anti-inflammatory interactions of aspartame with opioids and NSAIDs

The purpose of the present study was to investigate analgesic and anti-inflammatory properties of aspartame, an artificial sweetner and its combination with various opioids and NSAIDs for a possible synergistic response. The oral administration of aspartame (2-16mg/kg, po) significantly increased the pain threshold against acetic acid-induced writhes in mice. Co-administration of aspartame (2mg/kg, po) with nimesulide (2 mg/kg, po) and naproxen (5 mg/kg, po) significantly reduced acetic acid-induced writhes as compared to effects per se of individual drugs. Similarly when morphine (1 mg/kg, po) or pentazocine (1 mg/kg, po) was co-administered with aspartame it reduced the number of writhes as compared to their effects per se. Aspartame (4,8,16 mg/kg, po) significantly decreased carrageenan-induced increase in paw volume and also reversed the hyperalgesic effects in rats in combination with nimesulide (2 mg/kg, po).The study indicated that aspartame exerted analgesic and anti-inflammatory effects on its own and have a synergistic analgesic response with conventional analgesics of opioid and non-opioid type, respectively.     

Conformation of Prostaglandins

ALTHOUGH different prostaglandins^* may have different pharmacological effects, in general the compounds have the same qualitative action on a given cell type. Investigation^1,2 has revealed structure-activity correlations and the importance of the orientation of the 11 and 15 hydroxyl groups³ is recognized. Molecular model building together with structure-activity data have suggested that prostaglandins are one of a number of classes of drugs and hormones that seem to fit stereochemically into a pre-existing (for example, polypeptide-nucleotide) receptor site^4,5. The restraints applied to the prostaglandin molecule to fix it as a stable conformational isomer, or conformer, are little understood and we now wish to indicate the significance of this conformation with respect to interaction with biological membranes.     

Conformation of physalaemin

The conformational and spatial configuration of the biologically active undecapeptide physalaemin was studied using 350-MHz1H NMR. The NMR analyses suggested the existence of a strong hydrogen bond between the amide proton of the Phe7 and a carbonyl group in the N-terminal moiety, most likely the Pro4 one. Other bondings were postulated, involving the side-chain amine of Lys6 and the side-chain amide of Asn5 and respectively the side-chain carboxyl of Asp3 and the terminal amide carbonyl of Met-NH2. Thus unlike its shorter peptidic fragments, physalaemin exhibited a stable molecular structure in solution, giving some insight into the conformation required for interaction at the biological receptor of tachykinins.     

Conformation of dipeptides

The amide bond in L ,L - and L ,D -α-chloropropionylalanine methyl ester is shown to be trans by molar polarization and infrared spectroscopy. In these dipeptide diastereoisomer analogues, therefore, differences in physical properties, i.e., melting points, crystalline forms, gas chromatographic mobilities, etc., depend on preferred molecular conformations and not peptide bond configuration. Nuclear magnetic resonance spectra of both compounds were identical, indicating that no major chemical environment differences exist, which might have resulted from dissimilar side group interactions. Based on the data reported here and those of others, most dipeptide conformations can be eliminated because of contradiction with limits set by experimental or theoretical considerations. Of the remaining conformational possibilities, a single pair accounts for observed physical differences in dipeptide diastereoisomers, free or blocked. The preferred form contains α-hydrogens trans to each other and in the plane of the peptide bond. In this conformation, R¹–R² and amino–carboxyl distances are minimal in L ,D diastereomers and maximal in L ,L forms.     

On the sweetness of N-(trifluoroacetyl)aspartame

A panel of tasters has found that the N-trifluoroacetyl derivative of aspartame is five times less sweet than the parent compound, contrary to the tenet in the literature, but consistent with sweet receptor models which require this nitrogen to exist in protonated form.     

On the Sweetness of N-(Trifluoroacetyl)aspartame

A panel of tasters has found that the N-trifluoroacetyl derivative of aspartame is five times less sweet than the parent compound, contrary to the tenet in the literature, but consistent with sweet receptor models which require this nitrogen to exist in protonated form.     

Sweetening ruthenium and osmium: organometallic arene complexes containing aspartame

The novel organometallic sandwich complexes [(eta(6)-p-cymene)Ru(eta(6)-aspartame)](OTf)(2) (1) (OTf = trifluoromethanesulfonate) and [(eta(6)-p-cymene)Os(eta(6)-aspartame)](OTf)(2) (2) incorporating the artificial sweetener aspartame have been synthesised and characterised. A number of properties of aspartame were found to be altered on binding to either metal. The pK (a) values of both the carboxyl and the amino groups of aspartame are lowered by between 0.35 and 0.57 pH units, causing partial deprotonation of the amino group at pH 7.4 (physiological pH). The rate of degradation of aspartame to 3,6-dioxo-5-phenylmethylpiperazine acetic acid (diketopiperazine) increased over threefold from 0.12 to 0.36 h(-1) for 1, and to 0.43 h(-1) for 2. Furthermore, the reduction potential of the ligand shifted from -1.133 to -0.619 V for 2. For the ruthenium complex 1 the process occurred in two steps, the first (at -0.38 V) within a biologically accessible range. This facilitates reactions with biological reductants such as ascorbate. Binding to and activation of the sweet taste receptor was not observed for these metal complexes up to concentrations of 1 mM. The factors which affect the ability of metal-bound aspartame to interact with the receptor site are discussed.     

Comparison of aspartame and 4-chloroaspartame taste characteristics in rats and monkeys

Chloroaspartame, L-aspartyl-L-4-chlorophenylalanine methyl ester,(1), was synthesized from chlorophenylalanine methyl ester andthe thioanhydride of aspartic acid. Taste characteristics of1 and aspartarrune (2) were studied using the conditioned-flavoraversion (generalization) method with rats and using simplepreference tests with monkeys. Rats generalized an aversionfrom 2 to sucrose, HC1 and quinine; whereas, with 1 they generalizedonly to HC1 and quinine. Thus, in rats the sucrose-like ‘sweet’component is lost upon the introduction of a chloro substituentat the para position of the phenyl ring in aspartame. Consistentwith these results monkeys preferred 2 over water but this preferencewas reduced with 1.     

抑丝酶家族构象与疾病

抑丝酶超家族有高度保守的空间结构，分子内反应中心环酶β－片层引起构象重排是大多数抑丝酶生物学作用的结构基础。抑丝酶分子突变或由此所致的环－片层多聚体，使抑丝酶生物学作用降低或丧失，导致抑丝酶相关性疾病产生。     

Conformation of triphosphate and lysine-triphosphate-arginine complex

The semi-empirical all-valence electron CNDO/2 MO method has been used to calculate energy states of phosphate and triphosphate made analogous to ATP by adding a methyl group at one end and by making charge transfer complexes with arginine and lysine analogs. The calculations suggest that when ATP is attached to arginine and lysine residues, as is known to occur in actin, ATP is in a low energy state.