Octoxynol presence in bear-bile.

The presence of octoxynol from dried bear-bile was examined. Octoxynol was coextracted when glycolipids by Folch-Suzuki partition method. Octoxynol formed mixed-micelles with glycosphingolipids. The glycolipids were purified by DEAE-Sephadex A-25 column chromatography. The fractions containing mixed micelles were obtained from linear gradient solvent of 0.05M-0.5M ammonium acetate in methanol. HPLC ( Bondapak-NH(2) - linked to a Bondapak-C(18) column) chromatogram showed five peaks. Two possible structures for the fourth peak fraction were proposed as (CH(3))(3)C-CH(2)-C(CH(3))(2)-C(6)H(4)-OR and (CH(3))(3)C-C(CH(3))(2)-CH(2)-C(6)H(4)-OR by NMR spectroscopy. The structure was further confirmed by electrospray tandem mass spectrometry (ESI MS/MS). The spectrum showed a protonated molecule at m/z 559 and three different series of ions with mass difference of 44 were detected in the MS/MS spectrum. Therefore, the structure of the fourth peak fraction from HPLC was confirmed as octoxynol, (CH(3))(3)C-CH(2)-C(CH(3))(2)-C(6)H(4)-(OCH(2)-CH(2))n-OH, based on mass spectrometry and NMR spectroscopy.

Solution structure of reactive-site hydrolyzed turkey ovomucoid third domain by nuclear magnetic resonance and distance geometry methods.

The solution structure of reactive-site hydrolyzed turkey ovomucoid third domain (OMTKY3*) was determined by n.m.r. methods. A total of 655 distance constraints was applied in a distance geometry/simulated annealing approach to calculate a family of structures consistent with the n.m.r. data. The input data included 24 torsion angle constraints, 14 hydrogen bonds, 611 constraints derived from two-dimensional nuclear Overhauser enhancement spectroscopy data, and three disulfide bridges. Stereospecific assignments were included for the hydrogens of 26 beta-methylene groups and for seven isopropyl methyl groups (46% chiral assignments). OMTKY3* in solution retains the global fold and overall secondary structure of the intact inhibitor (OMTKY3) but exhibits local structural differences at and adjacent to the clip site. In particular, the hydrogen-bonding network observed at the reactive-site of the intact inhibitor is disrupted, and the position of Tyr20 is altered in the modified inhibitor. No evidence was found for ion pairing between the oppositely charged termini at the clip site. Surprisingly, in light of numerous changes indicating that OMTKY3* is less stable than OMTKY3, rotation of the Tyr31 ring was found to be slow in OMTKY3* at 30 degrees C. In OMTKY3, slow rotation of the Tyr31 ring was observed only at temperatures below 15 degrees C. The n.m.r. structures of OMTKY3* are compared here with the similarly calculated structures of OMTKY3. This represents the first comparison of an intact and modified (reactive-site clipped) proteinase inhibitor under identical conditions. On comparison with published X-ray structures of modified avian ovomucoid third domains from two other species, the present structure of OMTKY3* in solution was found to resemble that of the Japanese quail protein (OMJPQ3*) more closely than that of the more closely homologous silver pheasant protein (OMSVP3*).

Structural changes at the metal ion binding site during the phosphoglucomutase reaction.

An electron density map of the reactive, Cd2+ form of crystalline phosphoglucomutase from X-ray diffraction studies shows that the enzymic phosphate donates a nonbridging oxygen to the ligand sphere of the bound metal ion, which appears to be tetracoordinate. 31P and 113Cd NMR spectroscopy are used to assess changes in the properties of bound Cd2+ produced by substrate/product and by substrate/product analog inhibitors. The approximately 50 ppm downfield shift of the 113Cd resonance on formation of the complex of dephosphoenzyme and glucose 1,6-bisphosphate is associated with the initial sugar-phosphate binding step and likely involves a change in the geometry of the coordinating ligands. This interpretation is supported by spectral studies involving various complexes of the active Co2+ and Ni(2+)-enzyme. In addition, there is a loss of the 31P-113Cd J coupling that characterizes the monophosphate complexes of the Cd2+ enzyme either during or immediately after the PO3- transfer step that produces the bisphosphate complex, indicating a further change at the metal binding site. The implications of these observations with respect to the PO3- transfer process in the phosphoglucomutase reaction are considered. The apparent plasticity of the ligand sphere of the active site metal ion in this system may allow a single metal ion to act as a chaperone for a nonbridging oxygen during PO3- transfer or to allow a change in metal ion coordination during catalysis. A general NMR line shape/chemical-exchange analysis for evaluating binding in protein-ligand systems when exchange is intermediate to fast on the NMR time scale is described. Its application to the present system involves multiple exchange sites that depend on a single binding rate, thereby adding further constraints to the analysis.

Assignment of the 13C-NMR spectra of virgin and reactive-site modified turkey ovomucoid third domain.

The virgin (reactive-site Leu18-Glu19 peptide bond intact) and modified (reactive-site Leu18-Glu19 peptide bond hydrolyzed) forms of turkey ovomucoid third domain (OMTKY3 and OMTKY3*, respectively) have been analyzed by proton-detected 1H(13C) two-dimensional single-bond correlation (1H[13C]SBC) spectroscopy. Previous 1H-nmr assignments of these proteins [A.D. Robertson, W.M. Westler, and J.L Markley (1988) Biochemistry, 27, 2519-2529; G. I. Rhyu and J. L. Markley (1988) Biochemistry, 27, 2529-2539] have been extended to directly bonded 13C atoms. Assignments have been made to 52 of the 56 backbone 13C alpha-1H units and numerous side-chain 13C-1H groups in both OMTKY3 and OMTKY3*. The largest changes in the 13C chemical shift upon conversion of OMTKY3 to OMTKY3* occur at or near the reactive site, and tend toward values observed in small peptides. Moreover, the side-chain prochiral methylene protons attached to the C gamma of Glu19 and C delta of Arg21 show nonequivalent chemical shifts in OMTKY3 but more equivalent chemical shifts in OMTKY3*. These results suggest that the reactive site region becomes less ordered upon hydrolysis of the Leu18-Glu19 peptide bond. Comparison of 13C alpha chemical shifts of OMTKY3 and bovine pancreatic trypsin inhibitor [D. Brühuiler and G. Wagner (1986) Biochemistry 25, 5839-5843; N. R. Nirmala and G. Wagner (1988) Journal of the American Chemical Society, 110, 7557-7558] with small peptide values [R. Richarz and K. Wüthrich (1978) Biopolymers, 17, 2133-2141] suggests that 13C alpha chemical shifts of residues residing in helices are generally about 2 ppm downfield of resonances from nonhelical residues.

Two-dimensional NMR studies of Kazal proteinase inhibitors. 2. Sequence-specific assignments and secondary structure of reactive site modified turkey ovomucoid third domain.

The solution structure of modified turkey ovomucoid third domain (OMTKY3*) was investigated by high-resolution proton NMR techniques. OMTKY3* was obtained by enzymatic hydrolysis of the scissile reactive site peptide bond (Leu18-Glu19) in turkey ovomucoid third domain (OMTKY3). All of the backbone proton resonances were assigned to sequence-specific residues except the NH's of Leu1 and Glu19, which were not observed. Over 80% of the side-chain protons also were assigned. The secondary structure of OMTKY3*, as determined from assigned NOESY cross-peaks and identification of slowly exchanging amide protons, contains antiparallel beta-sheet consisting of three strands (residues 21-25, 28-32, and 49-54), one alpha-helix (residues 33-44), and one reverse turn (residues 26-28). This secondary structure closely resembles that of OMTKY3 in solution [Robertson, A. D., Westler, W. M., & Markley, J. L. (1988) Biochemistry (preceding paper in this issue)]. On the other hand, changes in the tertiary structure of the protein near to and remote from the cleavage site are indicated by differences in the chemical shifts of numerous backbone protons of OMTKY3 and OMTKY3*.

Active-site serine phosphate and histidine residues of phosphoglucomutase: pH titration studies monitored by 1H and 31P NMR spectroscopy.

1H and 31P NMR pH titrations were conducted to monitor changes in the environment and protonation state of the histidine residues and phosphoserine group of rabbit muscle phosphoglucomutase on binding of metal ions at the activating site and of substrate (glucose phosphate) at the catalytic site. Imidazole C epsilon-H signals from 8 of the 10 histidines present in the free enzyme were observed in 1H NMR spectra obtained by a spin-echo pulse sequence at 470 MHz; their pH (uncorrected pH meter reading of a 2H2O solution measured with a glass electrode standardized with H2O buffer) titration properties (in 99% 2H2O) were determined. Three of these histidine residues, which have pKa values ranging from 6.5 to 7.9, exhibited an atypical pH-dependent perturbation of their chemical shifts with a pHmid of 5.8 and a Hill coefficient of about 2. Since none of the observed histidines has a pKa near 5.8, it appears that these three histidines interact with a cluster consisting of two or more groups which become protonated cooperatively at this pH. Binding of Cd2+ at the activating site of the enzyme abolishes the pH-dependent transition of these histidines; hence, the putative anion cluster may constitute the metal ion binding site, or part of it. Two separate 31P NMR peaks from phosphoserine-116 of the phosphoenzyme were observed between pH 6 and 9. Apparently, the metal-free enzyme exists as a pH-dependent mixture of conformers that provide two different environments, I and II, for the enzymic phosphate group; the transition of the phosphate group between these two environments is slow on the NMR time scale.(ABSTRACT TRUNCATED AT 250 WORDS)

Multinuclear magnetic resonance studies of metal ion binding sites of phosphoglucomutase.

Metal binding at the activating site of rabbit muscle phosphoglucomutase has been studied by 31P, 7Li, and 113Cd NMR spectroscopy. A 7Li NMR signal of the binary Li+ complex of the phosphoenzyme was not observed probably because of rapid transverse relaxation of the bound ion due to chemical exchange with free Li+. The phosphoenzyme-Li+-glucose 6-phosphate ternary complex is more stable, kinetically, and yields a well-resolved peak from bound Li+ at -0.24 ppm from LiCl with a line width of 5 Hz and a T1 relaxation time of 0.51 +/- 0.07 s at 78 MHz. When glucose 1-phosphate was bound, instead, the chemical shift of bound 7Li+ was -0.13 ppm; and in the Li+ complex of the dephosphoenzyme and glucose bisphosphate a partially broadened 7Li+ peak appeared at -0.08 ppm. Thus, the bound metal ion has a somewhat different environment in each of these three ternary complexes. The 113Cd NMR signal of the binary Cd2+ complex of the phosphoenzyme appears at 22 ppm relative to Cd(ClO4)2 with a line width of 20 Hz at 44.4 MHz. Binding of substrate and formation of the Cd2+ complex of the dephosphoenzyme and glucose bisphosphate broaden the 113Cd NMR signal to 70 Hz and shift it to 75 ppm. The 53 ppm downfield shift upon the addition of substrate along with 1H NMR data suggests that one oxygen ligand to Cd2+ in the binary complex is replaced by a nitrogen ligand at some intermediate point in the enzymic reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme-bound intermediates in the conversion of glucose 1-phosphate to glucose 6-phosphate by phosphoglucomutase. Phosphorus NMR studies.

The interactions between metal ions and the phospho form of rabbit muscle phosphoglucomutase (EC 2.7.5.1) have been studied by 31P NMR. In the metal-free enzyme, the width at half-height of the 31P signal is 10 +/- 1 Hz at 81 MHz. In enzyme-Cd2+ complexes, the presence of spin-spin coupling with 113Cd2+ (J113Cd-O-31P = 16 Hz) and the absence of such splitting with 114Cd2+ indicate that Cd2+ binds directly to the enzymic phosphate. The absence of detectable splitting on transfer of the phosphate group to the acceptor hydroxyl group of bound glucose 1-phosphate, or glucose 6-phosphate (to give the 113Cd2+ complex of the dephospho-enzyme and glucose 1,6-bisphosphate), indicates that this transfer eliminates the direct metal ion-phosphate interaction. The enzyme-catalyzed reaction is slowed sufficiently by the addition of Li+ to allow studies of three discrete intermediate complexes by NMR techniques: glucose 1-phosphate bound to the phosphoenzyme, glucose 1,6-bisphosphate bound to the dephosphoenzyme (only one complex of this type was observed), and glucose 6-phosphate bound to the phosphoenzyme. Complete assignments of the phosphorus resonances of these intermediates have been made by labeling the phosphate ester group of either the enzyme or the sugar with 17O and by NMR polarization transfer studies. The effect of bound metal ions on these resonances also was determined. A 31P NMR titration study of the Li+ complex of the dephosphoenzyme with glucose 1,6-bisphosphate and a 31P NMR polarization transfer experiment indicate that beta-glucose 1,6-bisphosphate binds to the enzyme less tightly than alpha-glucose 1,6-bisphosphate.(ABSTRACT TRUNCATED AT 250 WORDS)