Effect of ethylene glycol on the interaction of different myosin subfragment 1.nucleotide complexes with actin

To elucidate the structure of the cross-bridge intermediates in the actomyosin ATPase cycle, several laboratories have added both ethylene glycol and AMP-PNP to muscle fibers. These studies suggested that ethylene glycol shifts the structure of myosin.AMP-PNP toward the weak-binding conformation, i.e., toward the structure of myosin.ATP. Since only the weak-binding conformation of myosin subfragment 1 (S-1) binds with no apparent cooperativity to the troponin-tropomyosin-actin complex (regulated actin), we used this as a probe to examine the conformation of various S-1.nucleotide complexes in ethylene glycol. Our results show that ethylene glycol markedly weakens the binding strength of S-1, S-1.ADP, and S-1.AMP-PNP to actin but has almost no effect on the binding strength of S-1.ATP. As in muscle fibers, at 40% ethylene glycol, the binding strength of S-1.AMP-PNP to actin becomes very similar to the binding strength of S-1.ATP. In the presence of troponin-tropomyosin, the binding of S-1.AMP-PNP to actin shows no apparent cooperativity in 40% ethylene glycol. Therefore, our results confirm that ethylene glycol shifts the structure of the myosin.AMP-PNP toward the weak-binding conformation. However, our results also suggest that ethylene glycol has a direct effect on the regulated actin complex. This is shown by the fact that ethylene glycol markedly increases the cooperative binding of S-1.ADP to regulated actin both in the presence and in the absence of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

Generation of selective microenvironment at the cell periphery through bulk-phase hydrophilic polymers

In order to understand the previously demonstrated effect of poly(ethylene glycol) on the stimulation of lymphocyte responses to syngeneic tumor cells (Ben-Sasson, S.A. and Henkart, P.A. (1977) J. Immunol. 119, 227–231), we have investigated the effects of addition of poly(ethylene glycol) to the medium in a number of cellular systems. The binding of trimeric IgG to tumor-lymphocyte Fc receptors was greatly enhanced by poly(ethylene glycol); a substantial increase in binding of trimeric IgG to non-Fc-receptor-bearing tumor cells was also observed. Similarly, the binding of labeled bovine serum albumin to lymphocyte surfaces was increased by poly(ethylene glycol), implying that nonspecific binding of proteins to cells was generally enhanced. The dose-response curve of concanavalin A mitogenesis was shifted to the right, as would be expected from a local increase in concanavalin A concentration. Antibody binding to erythrocytes as detected by complement lysis was similarly increased. It was found that in aqueous two-phase mixtures created by poly(ethylene glycol) and dextran, erythrocytes partition into the dextran phase through exclusion into dextran-rich microdroplets. It is proposed that addition of poly(ethylene glycol) to cell culture media creates a similar separate phase around the cell surface in which the local concentration of proteins is greater than that in the bulk medium. This concept explains many of the diverse effects of addition of poly(ethylene glycol) to the medium. It also can partially explain the requirement for serum to observe the poly(ethylene glycol) effect on the lymphocyte response to syngeneic tumor cells.     

A 2,2"-bipyridine ligand for incorporation into oligodeoxynucleotides: synthesis, stability and fluorescence properties of ruthenium-DNA complexes.

A non-nucleoside linker based upon the ligand 2,2'-bipyridine and ethylene glycol is prepared and placed into the backbone of a number of oligonucleo-tides. The bipyridine ligand is reacted with cis -dichloro bis(2,2'-bipyridyl) Ru(II) to generate the relatively substitutionally inert complex based upon the well-characterized tris -2,2'-bipyridyl Ru(II). The ruthenium-containing DNA complexes exhibited UV and fluorescence characteristics that are consistent with those previously observed for simple tris -2,2'-bipyridyl Ru(II) complexes. Oligonucleotides containing the ruthenium complex will form both DNA duplexes and triplexes with stabilities that are slightly better than those formed from simple tethered oligonucleotide probes in which the two hybridizing sequences are tethered by simple tri(ethylene glycol) or hexa(ethylene glycol) linkers.     

X-ray and NMR characterization of covalent complexes of trypsin, borate, and alcohols

An understanding of the physiological and toxicological properties of borate and the utilization of boronic acids in drug development require a basic understanding of borate-enzyme chemistry. We report here the extension of our recent NMR studies indicating the formation of a ternary borate-alcohol-trypsin complex. Crystallographic and solution state NMR studies of porcine trypsin were performed in the presence of borate and either of three alcohols designed to bind to the S1 affinity subsite: 4-aminobutanol, guanidine-3-propanol, and 4-hydroxymethylbenzamidine. Quaternary complexes of trypsin, borate, S1-binding alcohol, and ethylene glycol (a cryoprotectant), as well as a ternary trypsin, borate, and ethylene glycol complex have been observed in the crystalline state. Borate forms ester bonds to Ser195, ethylene glycol (two bonds), and the S1-binding alcohol (if present). Spectra from (1)H and (11)B NMR studies confirm that these complexes also exist in solution and also provide evidence for the formation of ternary trypsin, borate, and S1-subsite alcohol complexes which are not observed in the crystals using our experimental protocols. Analysis of eight crystal structures indicates that formation of an active site borate complex is in all cases accompanied by a significant (approximately 4%) increase in the b-axis dimension of the unit cell. Presumably, our inability to observe the ternary complexes in the crystalline state arises from the lower stability of these complexes and consequent inability to overcome the constraints imposed by the lattice contacts. A mechanism for the coupling of the lattice contacts with the active site that involves a conformational rearrangement of Gln192 is suggested. The structures presented here represent the first crystallographic demonstration of covalent binding of an enzyme by borate.     

Binding of ADP to rat liver cytosolic proteins and its influence on the ratio of free ATP/free ADP.

In a cytosolic extract from rat liver, the number and the concentration of ADP-binding sites as well as their dissociation constants were determined by using the rate-of-dialysis technique. Interfering cytosolic adenylate kinase was extracted from the cytosol by affinity chromatography on Ap5A-agarose, and remaining traces of enzyme activity were inhibited with (+)-catechin. Binding of ADP to cytosolic proteins was increased by poly(ethylene glycol) and decreased by EDTA. The effect of 0.1 mM-EDTA could be reversed by addition of equimolar concentrations of Mn2+ or Mg2+. In presence of 5% poly(ethylene glycol), added to increase local protein concentration, two binding sites for ADP were observed, with KD values of 1.9 microM (site I) and 10.8 microM (site II). The concentration of these binding sites, when extrapolated to cellular protein concentrations, were 30 microM (site I) and 114 microM (site II). It is concluded that a minimum of about 50% of total cytosolic ADP is bound to proteins, and that the ratio of free ATP/free ADP is at least twice that of total ATP/total ADP.     

New evidence for the mechanism of the tin(II) chloride catalyzed reactions of vicinal diols with diazodiphenylmethane in 1,2-dimethoxyethane

A kinetic study of the tin(II) chloride catalyzed reaction of diazodiphenylmethane with ethylene glycol in dimethoxyethane is reported. The preparation and characterization of ethylene glycol monodiphenylmethyl ether, the main product from this reaction, is also reported as well as the preparation of the two diphenylmethyl monoethers of methyl 4,6-O-benzylidene-alpha-D-glucopyranoside. An unexpected relationship between the concentration of ethylene glycol and the pseudo first-order rate constant, k', was observed in these reactions. For low concentrations of ethylene glycol (below 0.06 M), k' increases with increasing concentration of the diol. This trend is reversed for high concentrations of ethylene glycol (from about 0.06 to about 0.2 M). The apparent rate constant was also inversely related to the initial concentration of diazodiphenylmethane for the concentrations investigated. These results make the previously proposed involvement of a 1,3,2-dioxastannolane intermediate very unlikely [Petursson, S.; Webber, J.M. Carbohydr. Res. 1982, 103, 41-52]. The results suggest that more likely intermediates for these reactions involve tin(II) chloride complexes in a dynamic equilibrium with the diol.     

Modification of the interactions of myosin with actin and 5''-adenylyl imidodiphosphate by substitution of ethylene glycol for water.

We studied the effect of replacing water by ethylene glycol as solvent on the properties of skeletal muscle myosin, myosin subfragment-1 (S1) and heavy meromyosin. Ethylene glycol (50%, v/v) had no detectable effect on the affinity of myosin or actomyosin for the substrate analogue 5'-adenylyl imidodiphosphate (AMPPNP). However, the rate constants for formation and dissociation of the myosin X MgAMPPNP complex were reduced 200-fold; the logarithm of the dissociation rate was roughly proportional to the fractional concentration of ethylene glycol. Nucleotide dissociation was accelerated at least 300-fold by pure actin but remained slow with regulated actin in the absence of Ca2+. Ethylene glycol substitution reduced the affinity of S1 and the S1 X MgAMPPNP complex for actin equally (100-fold at 50% ethylene glycol). These results show that ethylene glycol has specific effects on myosin's enzymic mechanism, which can account for its effect on the tension and stiffness of glycerinated muscle fibres.     

Aggregation and fusion of unilamellar vesicles by poly(ethylene glycol)

Various aspects of the interaction between the fusogen, poly(ethylene glycol) and phospholipids were examined. The aggregation and fusion of small unilamellar vesicles of egg phosphatidylcholine (PC), bovine brain phosphatidylserine (PS) and dimyristoylphosphatidylcholine (DMPC) were studied by dynamic light scattering, electron microscopy and NMR. The fusion efficiency of Dextran, glycerol, sucrose and poly(ethylene glycol) of different molecular weights were compared. Lower molecular weight poly(ethylene glycol) are less efficient with respect to both aggregation and fusion. The purity of poly(ethylene glycol) does not affect its fusion efficiency. Dehydrating agents, such as Dextran, glycerol and sucrose, do not induce fusion. 31P-NMR results revealed a restriction in the phospholipid motion by poly(ethylene glycol) greater than that by glycerol and Dextran of similar viscosity and dehydrating capacity. This may be associated with the binding of poly(ethylene glycol) to egg PC, with a binding capacity of 1 mol of poly(ethylene glycol) to 12 mol of lipid. Fusion is greatly enhanced below the phase transition for DMPC, with extensive fusion occurring below 6% poly(ethylene glycol). Fusion of PS small unilamellar vesicles depends critically on the presence of cations. Large unilamellar vesicles were found to fuse less readily than small unilamellar vesicles. The results suggest that defects in the bilayer plays an important role in membrane fusion, and the 'rigidization' of the phospholipid molecules facilitates fusion possibly through the creation of defects along domain boundaries. Vesicle aggregation caused by dehydration and surface charge neutralization is a necessary but not a sufficient condition for fusion.     

Effects of ethylene glycol and methanol on ammonia-induced structural changes of the oxygen-evolving complex in photosystem II

Ammonia is an inhibitor of water oxidation and a structural analogue for substrate water, making it a valuable probe for the structural properties of the possible substrate-binding site on the oxygen-evolving complex (OEC) in photosystem II (PSII). By using the NH(3)-induced upshift of the 1365 cm(-)(1) IR mode in the S(2)Q(A)(-)/S(1)Q(A) spectrum and the NH(3)-modified S(2) state EPR signals of PSII as spectral probes, we found that ethylene glycol has clear effects on the binding properties of the NH(3)-specific site on the OEC. Our results show that in PSII samples containing 30% (v/v) ethylene glycol, the affinity of the NH(3)-specific binding site on the OEC is estimated to be more than 10 times lower than that in PSII samples containing 0.4 M sucrose. In addition, our results show that the NH(3)-induced upshift of the 1365 cm(-)(1) IR mode in the S(2)Q(A)(-)/S(1)Q(A) spectrum is dependent on the concentration of ethylene glycol, but not dependent on the concentration of sucrose (up to 1.5 M) or methanol (up to 5.4 M). By comparing the concentration dependence of sucrose and ethylene glycol on NH(3)-induced spectral change and also by comparing the sucrose and ethylene glycol data at similar concentrations ( approximately 1 M), we conclude that ethylene glycol has a clear effect on the NH(3)-induced spectral changes. Furthermore, our results also show that ethylene glycol alters the steric requirement of the amine effect on the upshift of the 1365 cm(-)(1) mode in the S(2)Q(A)(-)/S(1)Q(A) spectrum. In PSII samples containing 30% (v/v) ethylene glycol, only NH(3), not other bulkier amines (e.g., Tris, AEPD, and CH(3)NH(2)), has a clear effect on the upshift of the 1365 cm(-)(1) mode in the S(2)Q(A)(-)/S(1)Q(A) spectrum; in contrast, in PSII samples containing 0.4 M sucrose, both NH(3) and CH(3)NH(2) have a clear effect. On the basis of the results mentioned above, we propose that ethylene glycol acts directly or indirectly to decrease the affinity or limit the accessibility of NH(3) and CH(3)NH(2) to the NH(3)-specific binding site on the OEC in PSII. Finally, we also applied the same approach to test whether methanol is able to compete with ammonia on its binding site on the OEC. We found that 4% (v/v) methanol does not have any significant effect on the NH(3)-induced upshift of the 1365 cm(-)(1) mode in the S(2)Q(A)(-)/S(1)Q(A) spectrum and the NH(3)-modified S(2) state g = 2 multiline EPR signal. Our results suggest that methanol is unable to compete with NH(3) upon binding to the Mn site of the OEC that gives rise to the altered S(2) state g = 2 multiline EPR signal.     

Steady-state kinetic mechanism of recombinant avocado ACC oxidase: initial velocity and inhibitor studies

The gaseous plant hormone ethylene modulates a wide range of biological processes, including fruit ripening. It is synthesized by the ascorbate-dependent oxidation of 1-aminocyclopropyl-1-carboxylate (ACC), a reaction catalyzed by ACC oxidase. Recombinant avocado (Persea americana) ACC oxidase was expressed in Escherichia coli and purified in milligram quantities, resulting in high levels of ACC oxidase protein and enzyme activity. An optimized assay for the purified enzyme was developed that takes into account the inherent complexities of the assay system. Fe(II) and ascorbic acid form a binary complex that is not the true substrate for the reaction and enhances the degree of ascorbic acid substrate inhibition. The K(d) value for Fe(II) (40 nM, free species) and the K(m)'s for ascorbic acid (2.1 mM), ACC (62 microM), and O(2) (4 microM) were determined. Fe(II) and ACC exhibit substrate inhibition, and a second metal binding site is suggested. Initial velocity measurements and inhibitor studies were used to resolve the kinetic mechanism through the final substrate binding step. Fe(II) binding is followed by either ascorbate or ACC binding, with ascorbate being preferred. This is followed by the ordered addition of molecular oxygen and the last substrate, leading to the formation of the catalytically competent complex. Both Fe(II) and O(2) are in thermodynamic equilibrium with their enzyme forms. The binding of a second molecule of ascorbic acid or ACC leads to significant substrate inhibition. ACC and ascorbate analogues were used to confirm the kinetic mechanism and to identify important determinants of substrate binding.     

Sequence-specific conjugates of oligo(2'-O-methylribonucleotides) and hairpin oligocarboxamide minor-groove binders: design, synthesis, and binding studies with double-stranded DNA

New conjugates of triplex-forming pyrimidine oligo(2'-O-methylribonucleotides) with one or two 'head-to-head' hairpin oligo(N-methylpyrrole carboxamide) minor-groove binders (MGBs) attached to the terminal phosphate of the oligonucleotides with a oligo(ethylene glycol) linker were synthesized. It was demonstrated that, under appropriate conditions, the conjugates form stable complexes with double-stranded DNA (dsDNA) similarly to triplex-forming oligo(deoxyribonucleotide) (TFO) conjugates containing 5-methylated cytosines. Kinetic and thermodynamic parameters of the complex formation were evaluated by gel-shift assay and thermal denaturation. Higher melting temperatures (Tm), faster complex formation, and lower dissociation constants (Kd) of the triple helices (6-7 nM) were observed for complexes of MGB-oligo(2'-O-methylribonucleotide) conjugates with the target dsDNA compared to the nonconjugated individual components. Interaction of MGB moieties with the HIV proviral DNA fragment was indicated by UV/VIS absorption changes at 320 nm in the melting curves. The introduction of thymidine via a 3',3'-type 'inverted' phosphodiester linkage at the 3'-end of oligo(2'-O-methylribonucleotide) conjugates (3'-protection) had no strong influence on triplex formation, but slightly affected complex stability. At pH 6.0, when one or two hairpin MGBs were attached to the oligonucleotide, both triplex formation and minor-groove binding played important roles in complex formation. When two 'head-to-head' oligo(N-methylpyrrole) ligands were attached to the same terminal phosphate of the oligonucleotide or the linker, binding was observed at pH >7.5 and at high temperatures (up to 74 degrees). However, under these conditions, binding was retained only by the MGB part of the conjugate.     

Cleavage of double helical DNA by Cu2+ ion in the presence of bisintercalator containing penta(ethylene glycol) connector chain

In designing new DNA recognizing and cleaving reagents, we introduce herein a bisacridine derivative (referred to as bisacridine) in which two acridine heterocycles are connected by a penta(ethylene glycol) bridging chain. This compound offers two possible functions: 1, stabilization of DNA bisacridine intercalator complex by metal ion. The penta(ethylene glycol) chain stabilizes metal ions binding to the phosphate site of DNA, where the penta(ethylene glycol) chain constitutes a part of a pseudomacrocyclic ligand for metal binding; and 2, enhancement of metal-assisted hydrolytic cleavage of DNA by means of a metal concentration effect by the pseudomacrocyclic ethereal chain. The binding isotherms of bisacridine with DNA in the presence of metal ions showed that the binding was mainly governed by the cation exchange reaction on the anionic DNA polymer chain, i.e., the exchange between metal ions and the cationic bisacridine. The bisacridine showed an increase DNA binding ability compared to quinacrine, the monoacridine counterpart, and caused an enhancement of DNA cleavage in the presence of Cu2+ ions. Additional experiments which included DNase 1 footprinting in the presence of bisacridine and the DNA cleavage by Cu2+/bisacridine using a 32P end-labelled DNA fragment, suggested that the Cu2(+)-assisted DNA cleavage sites in the presence of bisacridine were in reasonable overlap with the DNA binding sites of bisacridine.     

Highly sensitive detection of protein phosphorylation by using improved Phos-tag Biotin

We have previously shown that the dinuclear zinc(II) complex Phos-tag and its derivatives act as phosphate-capture molecules in aqueous solution under conditions of neutral pH. In this study, our aim was to develop more-advanced applications for the detection of phosphopeptides and phosphoproteins by using several newly synthesized Phos-tag derivatives, including a bisbiotinylated Phos-tag (BTL-108), a tetrakisbiotinylated Phos-tag (BTL-109), and a monobiotinylated Phos-tag with a dodeca(ethylene glycol) spacer (BTL-111), as well as the commercially available product BTL-104. Among these complexes, BTL-111 showed the best performance in Western blotting by an ECL system using HRP conjugated streptavidin. In addition, in a quartz-crystal microbalance analysis of a phosphoprotein, the presence of the long hydrophilic dodeca(ethylene glycol) spacer in a novel Phos-tag sensor chip coated with BTL-111 resulted in a greater sensitivity than was achieved with a similar chip coated with BTL-104. Moreover, a peptide microarray technique using the ECL system and BTL-111 permitted high-throughput assays for the specific and highly sensitive detection of protein kinase activities in cell lysates.     

Interaction of human calpains I and II with high molecular weight and low molecular weight kininogens and their heavy chain: mechanism of interaction and the role of divalent cations

Calpain I prepared from human erythrocytes was half-maximally and maximally activated at 23 and 35 microM calcium ion, and two preparations of calpain II from human liver and kidney were half-maximally activated at 340 and 220 microM calcium ion and maximally activated at 900 microM calcium ion, respectively. High molecular weight (HMW) and low molecular weight (LMW) kininogens isolated from human plasma and the heavy chain prepared from these proteins inhibited calpain I as well as calpain II. The molar ratios of calpains to HMW kininogen to give complete inhibition of calpains were 1.4 for calpain I and 2.0 for calpain II, and those of calpains to heavy chain were 0.40-0.66 for calpain I and 0.85 for calpain II. LMW kininogen did not completely inhibit the calpains even with an excess amount of kininogen. The apparent binding ratio of calpain to HMW kininogen estimated from the disc gel electrophoretic analysis, however, was found to be 2:1, whereas those of calpain to LMW kininogen and of calpain to heavy chain were found to be 1:1. Calpains and kininogens failed to form complexes in the absence of calcium ion. In the presence of calcium ion, however, they formed the complexes, which were dissociable by the addition of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. The minimum concentrations of calcium ion required to induce complex formation between calpain I and kininogens and calpain II and kininogens were 70 and 100 microM, respectively. Some other divalent cations such as Mn2+, Sr2+, and Ba2+ were also able to induce the complex formation between calpains and kininogens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ia antigens in plastic-embedded tissues: a post-embedding immunohistochemical study

The aim of the present study was to establish a plastic embedding technique that makes possible the immunohistochemical demonstration of class II major histocompatibility complex (MHC) antigens (Ia antigens) in undecalcified joint tissues. Therefore a series of fixatives and dehydrating agents was tested for saving Ia immunoreactivity by post-embedding immunostaining of thin sections (2 microns) of rat tissues that had been embedded in glycol methacrylate (GMA), and by comparing with cryostat sections. An indirect immunoperoxidase and the avidin-biotin complex (ABC) technique were used. Combined with fixation by 4% formaldehyde, dehydration with GMA was found to give the best preservation of Ia antigenicity, followed by dehydration with ethylene glycol. The thinness of tissue sections facilitated the association of Ia antigens with different subcellular compartments in distinct cell populations. These various patterns are described.     

Surface modification to reduce nonspecific binding of quantum dots in live cell assays

Nonspecific binding is a frequently encountered problem with fluorescent labeling of tissue cultures when labeled with quantum dots. In these studies various cell lines were examined for nonspecific binding. Evidence suggests that nonspecific binding is related to cell type and may be significantly reduced by functionalizing quantum dots with poly(ethylene glycol) ligands (PEG). The length of PEG required to give a significant reduction in nonspecific binding may be as short as 12-14 ethylene glycol units.     

Embryo development in vitro of cat oocytes cryopreserved at different maturation stages

The purpose of this study was to evaluate the ability of cat oocytes, at different stages of maturation, to survive after cryopreservation and to assess their subsequent development following IVM and IVF. In the initial toxicity trial, immature oocytes were exposed to different concentrations of DMSO and ethylene glycol (EG). Resumption of meiosis and metaphase II were evaluated after removal of the cryoprotectant and IVM. The highest rates of resumption of meiosis (51.4%) were achieved after exposure to 1.5 mol l(-1) of cryoprotectants, and no difference was observed with control oocytes. Metaphase II was obtained in 25.7% (P<0.01) and 22.9% (P<0.005) of oocytes exposed to 1.5 mol l(-1) of DMSO and ethylene glycol, although at lower rates than in control oocytes (54.4%). On the basis of this finding, 1.5 mol l(-1) of cryoprotectant was chosen for freezing cat oocytes at the germinal vesicle stage (immature) or at metaphase II stage (mature). Post-thaw viability was assessed by the evaluation of the embryo development in vitro. After fertilization, mature oocytes frozen in ethylene glycol cleaved in better proportions (38.7%) than immature oocytes (6.8%, P<0.001), and no differences were observed in the cleavage rate of oocytes frozen at different maturation stages with DMSO (immature 12.8%; mature 14.1%). Embryonic development beyond the 8-cell stage was obtained only when mature oocytes were frozen with ethylene glycol (11.3%). This study suggests that cryopreserved cat oocytes can be fertilized successfully and that their development in vitro is enhanced when mature oocytes are frozen with ethylene glycol. The stage of maturation may be a key element in improving cat oocyte cryopreservation.     

Preliminary molecular characterization and crystallization of mitochondrial respiratory complex II from porcine heart

The mitochondrial respiratory complex II, or succinate:ubiquinone oxidoreductase, is an integral membrane protein complex in both the tricarboxylic acid cycle (Krebs cycle) and aerobic respiration. The gene sequences of each complex II subunit were measured by RT-PCR. N-terminal sequencing work was performed to identify the mitochondrial targeting signal peptide of each subunit. Complex II was extracted from porcine heart and purified by the ammonium sulfate precipitation method. The sample was solubilized by 0.5% (w/v) sugar detergent n-decyl-beta-D-maltoside, stabilized by 200 mM sucrose, and crystallized with 5% (w/v) poly(ethylene glycol) 4000. Important factors for the extraction, purification and crystallization of mitochondrial respiratory complex II are discussed.     

Modulation of the interaction between aldolase and glycerol-phosphate dehydrogenase by fructose phosphates

Kinetics of fructose-1,6-disphosphate aldolase (EC 4.1.2.13) catalyzed conversion of fructose phosphates was analyzed by coupling the aldolase reactions to the metabolically sequential enzyme, glycerol-3-phosphate dehydrogenase (EC 1.1.1.8), which interacts with aldolase. At low enzyme concentration poly(ethylene glycol) was added to promote complex formation of aldolase and glycerol-phosphate dehydrogenase resulting in a 3-fold increase in KM of fructose-1,6-bisphosphate and no change in Vmax. Kinetic parameters for fructose-1-phosphate conversion changed inversely upon complex formation: Vmax increased while KM remained unchanged. Gel penetration and ion-exchange chromatographic experiments showed positive modulation of the interaction of aldolase and dehydrogenase by fructose-1,6-bisphosphate. The dissociation constant of the heterologous enzyme complex decreased 10-fold in the presence of this substrate. Fructose-1-phosphate or dihydroxyacetone phosphate had no effect on the dissociation constant of the aldolase-dehydrogenase complex. In addition, titration of fluorescein-labelled glycerol-phosphate dehydrogenase with aldolase indicated that both fructose-1,6-bisphosphate and fructose-2,6-biphosphate enhanced the affinity of aldolase to glycerol-phosphate dehydrogenase. The results of the kinetic and binding experiments suggest that binding of the C-6 phosphate group of fructose-1,6-bisphosphate to aldolase complexed with dehydrogenase is sterically impeded while saturation of the C-6 phosphate group site increases the affinity of aldolase for dehydrogenase. The possible molecular mechanism of the fructose-1,6-bisphosphate modulated interaction is discussed.     

Effect of the nature of the surface of disperse silica on its interaction with the reproductive cells and seminal plasma of cattle]

The interaction of various disperse silica of I, II, III kind possessing various structure of surface groups (-OH; -O-CH2-CH2-O-CH2-CH2OH; -O-CH2-CH2-NH2 respectively) was investigated with some above membrane matrix polymers of bovine reproductive cells and seminal plasma (namely the surface proteins and carbohydrate polymers containing the N-acetyl-neuraminic acid (NANA) as terminal residue). Protein binding was preferentially observed for silica surface modified by aminoethoxy--and ethylene glycol groups and depended on concentration of silica in the mixture. It was found that biopolymers containing carbohydrate groups had larger affinity to I than to II or III. The binding value of I-III was 12-16% with respect to plasma proteins. Silicas I and II with -OH-groups on the surface absorb 17-21% N-ANA-containing polymers of bovine seminal plasma.