Thaumatin and monellin are the two sweetest compounds known to man-about 100,000 times sweeter than sugar on a molar basis and 3000 times on a weight basis. These proteins represent a unique class of proteins that are tasteactive. We report the three-dimensional structure of thaumatin I at 3.1 A resolution.Taste is one of the least understood senses from a biochemical point of view. Sweet taste can be elicited to varying degrees by a wide variety of compounds in high concentration, such as mono-and disaccharides, several amino acids, dipeptide derivatives, glycerol, cyclamates, saccharine, acesulfame, some hydrated inorganic compounds, and others.Sensations of sweet taste are elicited by sweet compounds binding to sweet receptors of taste buds on the tongue, similar to hormone-hormone receptor binding. However, the similarity ends here. A 50% binding of hormone receptors usually occurs at around 10-8 to 10-11 M concentration of hormones, but in the case of sweet receptors the concentration to register sweet taste is about 10-1 to 10-3 M of sucrose. Furthermore, like other sensory perceptions, taste is associated with a unique set of sensation parameters. These are threshold concentration, onset time, intensity, saturation concentration, lingering time, aftertaste, and potentiation of other tastes or flavors. Systematic studies of these properties of taste-active compounds have been difficult in the past because of high levels of nonspecific binding between the sweet comnpounds and the sweet receptors due to the high concentrations of the sweet compounds required to elicit the sweet taste.One of the most interesting and unusual recent findings is the existence of two intensely sweet proteins, monellin and thaumatin (for a recent review, see ref. 1). The sweet taste of the proteins can be registered at a very low concentration (10' M), comparable to those in hormone-hormone receptor interaction. These proteins are about 100,000 times sweeter than sucrose on a molar basis and several thousand times sweeter on a weight basis. In fact, these two proteins are the two sweetest compounds known to man. With these proteins, studies similar to those performed for hormonehormone receptors can be initiated. Three-dimensional structures of these proteins are likely to provide a solid foundation upon which studies to understand the molecular basis of sweet taste can be designed. We here report the crystal structure of thaumatin I at 3.1 A resolution.Thaumatins have been isolated from the fruit of a West African rain forest shrub, Thaumatococcus daniellii Benth (2), which has been used for centuries by inhabitants of the region to sweeten foods such as bread and palm wine, There are two major sweet proteins in the fruit, thaumatin I and II, with almost identical molecular weights of 22,000. They consist of 207 amino acids and have identical amino acid sequences except for five residues (3, 4). There are no histidine residues, but there are eight disulfide bonds. Partially pure thaumatin is available commercially from Si...

From the reaction of m-(Me2NCH2)2C6H4 with aqueous rhodium trichloride in ethanol the ortho-metalated product trans-Rhn,Cl2(N-C-N)(H20) could be isolated in 45% yield (N-C-N = C6H3(CH2NMe2)2-o,oO. Its solid-state structure was determined by an X-ray diffraction study. Crystals are monoclinic, space group P7\jn, with lattice parameters a = 9.070 (1) Á, b = 17.277 (3) Á, c = 9.855 (1) Á, ß = 91.34 (1)°, V = 1543.9 (4) Á3, Z = 4, and ¿(caled) = 1.648 g cm"3. Refinement with 3710 observed reflections converged at R = 0.042. The structure of imni-RhnlCl2(N-C-N)(H20) consists of a rhodium(III) center that is octahedrally coordinated. A mer arrangement of the C and two N atoms of the monoanionic N-C-N ligand (Rh-C(aryl) = 1. 913 (3) Á) and a coordinated water molecule trans to C(aryl) form a planar arrangement. The two mutually trans Cl atoms sited above and below this plane complete the coordination sphere. In the solid state the molecules form infinite chains via intermolecular O-H-Cl hydrogen bonds. Metathesis of this new compound with either a large excess of alkali-metal salt or a slight excess of silver salt led to the formation of a range of new arylrhodium(III) compounds, rranr-RhX2(N-C-N)(H20) (X = Br, 02CH, 02CMe, N03, and CN). Halogen-bridged biand trinuclear complexes RhCl(N-C-N)^-Cl)2M(COD) (M = Rh1, Ir1; COD = 1,5cyclooctadiene) and [RhCl(N-C-N)(^-Cl)2]2M (M = Pd", Cu") were synthesized by mixing fra«y-RhCl2(N-C-N)(H20) with the appropriate metal salt: [MCl(COD)]2, CuCI2, and PdCl2(COD) or Li2PdCl4, respectively.' The same reaction with Li(acac)

A method is presented for the semi‐automatic indexing of the Laue diffraction pattern. The method is based on the recognition of conics in the Laue pattern by a plane‐search algorithm in reciprocal space, after which possible cells are constructed in direct space and relative cell parameters and crystal orientation are obtained. These cells, scaled to an arbitrary volume, are refined, reduced and grouped in order of frequency of occurrence. Usually, the cell that occurs most frequently is the correct one. Other cells found have one or more axes doubled. Such cells are easily discriminated by comparison of the corresponding simulated Laue pattern with the measured one. The method is tested with different data sets of an organic and an organometallic compound collected with an image plate using white radiation of a molybdenum sealed tube. For each pattern, the correct cell was found. Further refinement of the relative cell parameters by matching of the calculated and observed positions of the Lane spots showed good agreement with the relative cell parameters obtained from monochromatic data. To scale the cells, additional information is needed. This paper demonstrates the use of the Mo emission line Kβ1 to determine the cell volume within 1.2%.

The classical method of phase determination from Bijvoet inequalities is applied to the phase ~hk= ½(q~hk --Or, r,) of the triple product Zhk = FhFkFg-4-¢. The phase-determining formula is then (in the case of a centrosymmetric configuration of anomalous scatterers):[Zhk[ 2 --I~1 z sin ~hk= 4ZhklZOhkl in which Zhk is the contribution from the imaginary part of the complex double Patterson function to Zhk, and [Z~k[ 2 =~([Zhk]It is shown that Zhk contains an important term, i.e. the contribution from the origin peak of the double Patterson function, which is independent of the positions of the anomalous scatterers. A test calculation on a structure in P1, containing two Br ions, shows that, in fact, the phases of the triple products can be determined without introducing any a priori knowledge about the positions of the anomalous scatterers, provided an appropriate scaling procedure is applied.

A two-step procedure is presented for the estimation of triplet invariants from multi-wavelength data. In the first step wavelength-independent structure-factor magnitudes of both the total structure and the light-atom substructure, together with associated structure-factor phase differences, are calculated explicitlyviaa modified Singh & Ramaseshan [Acta Cryst. (1968), B24, 35-40] procedure. In the second step these quantities are employed as conditional information in the probability distribution of a triplet invariant which can be derived from Hauptman's [Acta Cryst.(1982), A38, 289-294] joint probability distribution for an isomorphous pair of structures. Test calculations on the structure of the iron-containing protein ferredoxin show the feasibility of the procedure.