Structure of native pancreatic elastase from North Atlantic salmon at 1.61 A resolution.

The crystal structure of native salmon pancreatic elastase (SPE) has been solved by molecular-replacement methods, and refined by conventional conjugate-gradient methods and simulated-annealing techniques. The final R value is 17.2% for 21 389 reflections between 8.0 and 1.61 A, and the corresponding free R value is 23.9%. The overall tertiary structure of SPE is remarkably similar to that of porcine pancreatic elastase I (PPE), to which it shows about 67% sequence identity. The primary structure of SPE is determined from the electron-density maps, and only about 15 side chains are somewhat uncertain. Interesting differences between SPE and PPE, are one sequence deletion assigned to position 186, the residue 192 at the entrance of the specificity pocket is substituted from a Gln in PPE to Asn in SPE, and one of the calcium ligands is different. Furthermore, electron density is missing in SPE for the last three residues of the C-terminal helix. A comparison of the present amino-acid sequence of SPE with other sequences available indicates that SPE belongs to the class 1 pancreatic elastases.

Structure of anionic salmon trypsin in a second crystal form.

Anionic salmon trypsin in a second crystal form (ST-IIB) has been refined at 1.83 A, resolution. The crystals are orthorhombic and belong to space group P2(1)2(1)2 with lattice parameters a = 77.09, b = 82.33 and c = 31.16 A. The present structure has been compared to salmon trypsin as it appears in a previously reported crystal form (ST-IIA) with cell dimensions a = 61.95, b = 84.33 and c = 39.11 A [Smalås & Hordvik (1993). Acta Cryst. D49, 318-330]. The presence of a sulfate group involved in several hydrogen bonds to active-site residues, and the location of an additional benzamidine site in the crystal lattice, are the most striking differences between the present and the previous structure. Superposition of main-chain atoms in the two structures give an overall r.m.s. difference of 0.26 A, with the main differences located to areas with different molecular packing. The overall coordinate error is estimated to be between 0.20 and 0.25 A, by the method of Luzzati.

Cold adaption of enzymes: structural comparison between salmon and bovine trypsins.

The crystal structure of an anionic form of salmon trypsin has been determined at 1.82 A resolution. We report the first structure of a trypsin from a phoikilothermic organism in a detailed comparison to mammalian trypsins in order to look for structural rationalizations for the cold-adaption features of salmon trypsin. This form of salmon trypsin (ST II) comprises 222 residues, and is homologous to bovine trypsin (BT) in about 65% of the primary structure. The tertiary structures are similar, with an overall displacement in main chain atomic positions between salmon trypsin and various crystal structures of bovine trypsin of about 0.8 A. Intramolecular hydrogen bonds and hydrophobic interactions are compared and discussed in order to estimate possible differences in molecular flexibility which might explain the higher catalytic efficiency and lower thermostability of salmon trypsin compared to bovine trypsin. No overall differences in intramolecular interactions are detected between the two structures, but there are differences in certain regions of the structures which may explain some of the observed differences in physical properties. The distribution of charged residues is different in the two trypsins, and the impact this might have on substrate affinity has been discussed.

Structure determination and refinement of benzamidine-inhibited trypsin from the North Atlantic salmon (Salmo salar) at 1.82 A resolution.

The structure of the serine protease trypsin from the North Atlantic salmon (Salmo salar) has been solved by molecular replacement and refined by restrained least-squares methods to a conventional R factor of 16.4% using diffractometer data in the 6.0-1.82 A resolution range (14 443 reflections greater than 3sigma). The model comprises 1793 protein atoms and 180 solvent molecules which were given unit occupancies, and the average temperature factors for protein atoms and solvent oxygen atoms are 15.2 and 36.8 A(2), respectively. The estimated error in atomic positions is about 0.2 A. The structure of salmon trypsin was solved and refined with only a small part of the amino-acid sequence known. However, a gene sequence of salmon trypsin has later become available. Some discrepancies between this sequence and the sequence obtained from the present X-ray crystal study indicate that the mentioned sequences may correspond to isoenzymes. The structure of salmon trypsin is similar to other trypsins of known structure.

Crystallization and preliminary X-ray crystallographic studies of CO-hemoglobin from the North Atlantic salmon (Salmo salar).

Purification of hemoglobin from North Atlantic salmon (Salmo salar) gave three different types. The CO-complexes of types I and III have been crystallized by the batch method at 4 degrees C from solutions 18% (w/v) in polyethylene glycol 2000, 50 mg/ml in hemoglobin and 0.05 M in phosphate buffer (pH 8.3). Orthorhombic crystals, space group P2(1)2(1)2(1), were obtained for both, with cell dimensions a = 53.9 A, b = 80.4 A, c = 132.4 A, and a = 58.7 A, b = 95.0 A, c = 107.4 A, for types I and III, respectively.

Crystallization and preliminary X-ray crystallographic studies of benzamidine-inhibited trypsin from the North Atlantic salmon (Salmo salar).

Crystals of benzamidine-inhibited trypsin from the North Atlantic salmon (Salmo salar) have been grown from ammonium sulphate solution at pH 5.0. Two crystal forms suitable for X-ray structure analysis, obtained from a hanging-drop experiment, have been characterized. Both belong to space-group P22(1)2(1) with cell dimensions a = 39.2 A, b = 62.4 A, c = 84.6 A and a = 31.4 A, b = 74.8 A, c = 83.5 A, for forms I and II, respectively. Intensity data to 1.82 A have been collected for crystal form I on a CAD4 diffractometer, and initial phases have been obtained by molecular replacement methods. The conventional R-factor after two rounds of model building and subsequent refinement is 0.25 for data between 6.0 and 2.0 A. So far no water molecules have been included in the model.

High-resolution (1.5 A) crystal structure of phospholipase C from Bacillus cereus.

Both the phosphatidylinositol-hydrolysing and the phosphatidylcholine-hydrolysing phospholipases C have been implicated in the generation of second messengers in mammalian cells. The phosphatidylcholine-hydrolysing phospholipase C (PLC) from Bacillus cereus, a monomeric protein containing 245 amino-acid residues, is similar to some of the corresponding mammalian proteins. This, together with the fact that the bacterial enzyme can mimic the action of mammalian PLC in causing, for example, enhanced prostaglandin biosynthesis, suggests that B. cereus PLC can be used as a model for the hitherto poorly characterized mammalian PLCs. We report here the three-dimensional structure of B. cereus PLC at 1.5 A resolution. The enzyme is an all-helix protein belonging to a novel structural class and contains, at least in the crystalline state, three Zn2+ in the active site. We also present preliminary results from a study at 1.9 A resolution of the complex between PLC and inorganic phosphate (Pi) which indicate that the substrate binds directly to the metal ions.

Photoacoustic technique for determining optical absorption coefficients in solids.

An investigation was made of a photoacoustic technique for determining the optical absorption coefficient in solids. A train of laser pulses was passed through the solid, and a piezoelectric transducer attached directly to the sample measured the amplitude of the elastic wave generated by the absorbed radiation. Calibration was performed at a wavelength of known absorption. The sensitivity of the technique was found to be limited to about 1 x 10(-5) cm(-1) in our samples due to radiation scattered onto the transducer, but the technique is capable of measuring absorption coefficients in the 10(-6)-cm(-1) range using laser powers of about 1 W.

Measurement techniques for small absorption coefficients: recent advances.

A review is given of several newly developed methods for measuring low absorption losses in optical rnaterials. Transmission, emittance, and calorimetric techniques are described with special emphasis on how thermocouple and photoacoustic calorimetry can be used to determine both bulk and surface absorption simultaneously. The advantages and disadvantages of the various approaches are discussed, and estimates are given of the sensitivities that can be achieved with the different techniques. Finally, a new ac interferometric calorimetric method for measuring low bulk losses is proposed.

Photoacoustic measurements of surface and bulk absorption in HF/DF laser window materials.

A new photoacoustic technique is used for quantitatively determining surface and bulk absorption losses at HF/DF laser wavelengths. Materials investigated include Si, GaAs, ZnSe, Al(2)O(3), MgO, MgF(2), CaF(2), SrF(2), BaF(2), LiF, and KMgF(3). Although several materials show predicted intrinsic bulk absorption at 3.8 microm, no material is found to exhibit predicted intrinsic absorption loss at 2.7 microm. High surface absorption at both HF and DF laser frequencies general ly dominate over-all absorption losses for most of the materials tested.

Characteristics of the optical parametric oscillator and its use for selective excitation.

Techniques are presented for obtaining stable, single mode output from an optical parametric oscillator and for aligning such an oscillator with a molecular or atomic transition. A line width of 10(-3) cm(-1) or less was obtained with a long term frequency stability of 10(-3) cm(-1) or better. It has been demonstrated that an OPO can stay aligned for several hours with an absorption line of half-width 0.01 cm(-1).