Evaluation of interaction between citrus flavonoid, naringenin, and pepsin using spectroscopic analysis and docking simulation

Computational Chemistry Strategies to Investigate the Antioxidant Activity of Flavonoids-An Overview

Despite several decades of research, the beneficial effect of flavonoids on health is still enigmatic. Here, we focus on the antioxidant effect of flavonoids, which is elementary to their biological activity. A relatively new strategy for obtaining a more accurate understanding of this effect is to leverage computational chemistry. This review systematically presents various computational chemistry indicators employed over the past five years to investigate the antioxidant activity of flavonoids. We categorize these strategies into five aspects: electronic structure analysis, thermodynamic analysis, kinetic analysis, interaction analysis, and bioavailability analysis. The principles, characteristics, and limitations of these methods are discussed, along with current trends.

Conformational dynamics of trypsin in the presence of caffeic acid: a spectroscopic and computational investigation

Caffeic acid is one of the widely distributed phenolic compounds in nature and can be found in planet products. On the other hand, trypsin is a vital digestive enzyme in the intestine that plays an essential role in the immune response, blood coagulation, apoptosis and protein maturation like protein digestion. Several studies have revealed the inhibitory effects of the phenolic compound on the digestive enzyme. The present study reports functional and conformational alteration of trypsin after caffeic acid addition using multiple experimental and computational techniques for the first time. The intrinsic fluorescence of trypsin is quenched in the presence of caffeic acid via a static mechanism. The percent of secondary structures (α-helix and β-sheet) of trypsin alter after caffeic acid addition. In the kinetic study, a reduction in the trypsin function is obtained with a lower Vmax and Kcat upon interaction with caffeic acid. The thermal study reveals an unstable structure of trypsin upon complex formation with this phenolic compound. Also, the binding sites and conformational changes of trypsin are elucidated through molecular docking and molecular dynamic simulation.Communicated by Ramaswamy H. Sarma.

Effect of glycation-induced concentration-dependent change in albumin structure and alteration in its binding capacity

Reducing sugars causes confirmatory alterations in albumin structure by the nonenzymatic glycation of the amino group of serum albumin. In this study, glucose and its hazardous metabolic products like glyoxal and methylglyoxal were incubated with bovine serum albumin (BSA). The confirmational changes in BSA molecule's structure by glycating substances was investigated using a variety of spectroscopic methods, including deconvolutionFourier Transform Infra-red (FT-IR) spectroscopy, fluorescence spectroscopy, UV spectroscopy and circular dichroism (CD) spectroscopy. Dynamic fluorescence quenching was observed in the case of glucose, while static quenching was observed in the case of methyl glyoxal and glyoxal. Similarly, employing deconvolution FT-IR spectroscopy and CD spectroscopy for determination of change in secondary structures in terms signature of α-helix, β-turn, β-sheet and random coil modifications. Destabilization or unfolding of the albumin structure, due to the disruption of the hydrogen bonding pattern that stabilizes the albumin manifold, causes a 25-50% reduction in α-helix and a 2-fold increase in β-sheet and turns in glycated BSA. The competitive displacement interaction studies with warfarin were performed using the ultrafiltration technique and quantitative determination of free drug in ultrafiltrate using LC-MS/MS. The binding of carbamazepine (CBZ) or its active metabolite to proteins was unaffected by the glycation of BSA with glucose and methyl glyoxal. Nevertheless, with glyoxal-modified BSA, it changed the binding of selected analytes significantly. Based on in vitro observations and results, it could be anticipated that the serum CBZ concentration variation may be worsened in uncontrolled diabetes circumstances, with an overall variance of 30-40% possible.Communicated by Ramaswamy H. Sarma.

Synthesis of 4-sulfamoyl phenyl diazocarboxylic acid derivatives as novel non-classical inhibitors of human carbonic anhydrase II activity: an in vitro study

The first class of carbonic anhydrase inhibitors (CAIs) discovered was sulfonamides, but their clinical use is limited due to side effects caused by their inhibition of multiple CA isoforms. To overcome this, researchers have focused on developing isoform-selective CAIs. This study involved the synthesis and characterization of novel carboxylic acid/sulfonamide derivatives. We investigated the interaction between these compounds and the human carbonic anhydrase II (hCA II) isoform using spectroscopic and computational methods. The synthesized compounds were evaluated based on their IC50, Kd and Ki values, and it was found that the inhibitory potency and binding affinity of the compounds increased with the number of carboxylic acids zinc binding groups. Specifically, the compound C4, with three carboxylic acid groups, showed the strongest inhibitory potency. Fluorescence measurements revealed that all compounds quenched the intrinsic fluorescence of hCA II through a dynamic quenching process, and each compound had one binding site in the hCA II structure. Thermodynamic analysis indicated hydrogen bonds and van der Waals interactions played key roles in the binding of these compounds to hCA II. Docking studies showed that the carboxylic acid groups directly attached to the zinc ion in the active site, displacing water/hydroxide ions and causing steric hindrance. Overall, the strengthening of inhibitory activity and the binding power of these carboxylic acid derivatives for the hCA II makes these compounds interesting for designing novel hCA II inhibitors.Communicated by Ramaswamy H. Sarma.

Molecular interaction studies of P3CL on bovine serum albumin through biophysical approach

In the fields of pharmacology and life sciences, it is essential to study how prescribed drugs interact with carrier proteins in human serum albumin. The current study has evaluated the binding properties of rhodanine derivative; (z)-2-(4-(5-((3-(3-chlorophenyl)-1-phenyl-1H-pyrazol-4-oxo-2-thioxothiazolidin-3-yl)benzamido)acetic acid (P3CL) on bovine serum albumin (BSA) by biophysical approach. BSA is a homology model of Human serum albumin. Due to the cost-effectiveness of Human Serum Albumin (HSA) we have studied the binding properties of rhodanine derivative (P3CL) on BSA. The BSA-P3CL interactions were investigated by fluorescence spectroscopy and revealed the presence of a static quenching mechanism. P3CL possesses good binding affinity on BSA with binding constant KP3CL = 5.36330 × 1013 M-1 binding free energy. We have calculated the binding free energy, the number of binding sites, and the binding constants. The establishment of hydrogen bonds and the active participation of amino acids in drug binding were confirmed by molecular docking studies. As conventional processes for the investigation of pharmacological drugs, therapeutic combinations, and coordinated drug intake, the offered strategies are simple to comprehend, accurate, and rapid to put into practice. Our findings will support an additional investigation into ligand's pharmacological activity.Communicated by Ramaswamy H. Sarma.

Evidence for paraquat-pepsin interaction: In vitro and silico study

The use of the herbicide paraquat (PQ) has raised concerns about potential environmental consequences due to its toxicity and persistence in the environment. Considering the affinity of dangerous compounds to biological molecules, it is necessary to know their binding properties. This article focuses on the behavior of the pepsin enzyme following its contact with paraquat poison, and the interaction between paraquat and pepsin has been investigated in laboratory conditions and simulated physiological conditions using multispectral techniques. Fluorescence experiments showed that PQ uses a static method to quench pepsin's intrinsic fluorescence. By causing structural damage to pepsin, PQ may be detrimental as it alters its conformational function based on FT-IR spectroscopy. The coupling reaction is a spontaneous process caused by hydrogen bonding and van der Waals forces according to the analysis of the thermodynamic parameters of each system at three different temperatures. The molecular structure of pepsin changes when it binds to PQ. Also, the results showed that PQ is a pepsin inhibitor that changes the function of the enzyme.

Exploring the impact of taurine on the biochemical properties of urate oxidase: response surface methodology and molecular dynamics simulation

This paper investigates the impact of taurine as an additive on the structural and functional stability of urate oxidase. First, the effect of the processing parameters for the stabilization of Urate Oxidase (UOX) using taurine was examined using the response surface methodology (RSM) and the central composite design (CCD) model. Also, the study examines thermodynamic and kinetic parameters as well as structural changes of urate oxidase with and without taurine. Fluorescence intensity changes indicated static quenching during taurine binding. The obtained result indicates that taurine has the ability to preserve the native structural conformation of UOX. Furthermore, molecular dynamics simulation is conducted in order to get insights into the alterations in the structure of urate oxidase in the absence and presence of taurine under optimal conditions. The molecular dynamics simulation section investigated the formation of hydrogen bonds (H-bonds) between different components as well as analysis of root mean square deviation (RMSD), root mean square fluctuations (RMSF) and secondary structure. Lower Cα-RMSD and RMSF values indicate greater stabilization of the taurine-treated UOX structure compared to the free enzyme. The results of molecular docking indicate that the binding of taurine to the UOX enzyme through hydrophobic interactions is associated with a negative value for the Gibbs free energy.

Structural alterations and inhibition of lysozyme activity upon binding interaction with rotenone: Insights from spectroscopic investigations and molecular dynamics simulation

The pervasive employment of pesticides such as rotenone on a global scale represents a substantial hazard to human health through direct exposure. Therefore, exploring the interactions between such compounds and body macromolecules such as proteins is crucial in comprehending the underlying mechanisms of their detrimental effects. The present study aims to delve into the molecular interaction between rotenone and lysozyme by employing spectroscopic techniques along with Molecular dynamics (MD) simulation in mimicked physiological conditions. The binding interaction resulted in a fluorescence quenching characterized by both dynamic and static mechanisms, with static quenching playing a prominent role in governing this phenomenon. The analysis of thermodynamic parameters indicated that hydrophobic interactions primarily governed the spontaneous bonding process. FT-IR and circular dichroism findings revealed structural alternations of lysozyme upon complexation with rotenone. Also, complexation with rotenone declined the biological activity of lysozyme, thus rotenone could be considered an enzyme inhibitor. Further, the binding interaction substantially decreased the thermal stability of lysozyme. Molecular docking studies showed the binding location and the key residues interacting with rotenone. The findings of the spectroscopic investigations were confirmed and accurately supported by MD simulation studies.

L-histidine-assisted ultrasound improved physicochemical properties of myofibrillar proteins under reduced-salt condition - Investigation of underlying mechanisms

The effects of the L-hisdine (L-His)-assisted ultrasound on physicochemical characteristics and conformation of myofibrillar protein (MP) under reduced-salt condition were investigated using spectroscopic analysis, and the binding mechanism between L-His and MP was further elucidated through molecular docking and molecular dynamics (MD) simulations. UV second derivative spectra and intrinsic Try fluorescence spectra revealed that L-His formed a complex with MP and altered the microenvironment of MP. After L-His-assisted ultrasound treatment, MP showed smaller particle size, higher solubility, and more uniform atomic force microscopy image due to the decrease of α-helix content and the subsequent increase in zeta potential, active sulfhydryl content, and surface hydrophobicity. Molecular docking and MD simulations demonstrated the optimal docking pose (minimum binding affinity of -6.78 kcal/mol) and revealed hydrophobic interactions and hydrogen bonds as the main interaction forces between L-His and MP, with several residues (ILE-464, ILE-480, THR-483, ASN-484, GLY-466, ASP-463, PHE-246) identified as binding sites.

Structural changes and anti-hepatocellular carcinoma activity of interferon-γ after interaction with sinensetin

Exploring the interaction of small molecules with therapeutic proteins can provide useful information about development of ligand-protein complexes as synergistically therapeutic platforms. In this study, the interaction of sinensetin with human interferon gamma (IFNγ) was evaluated experimentally and theoretically. Also, the synergistic effects of IFNγ- sinensetin complex on the inhibition of hepatocellular carcinoma HepG2 cell proliferation were assessed by cell viability and quantitative real time PCR assays. It was realized that sinensetin interacts with IFNγ through a static quenching mechanism and hydrophobic forces mediated by presence of Lys55 and Lys58 amino acid residues in the binding site were the main contributing forces in the spontaneous formation of IFNγ-sinensetin complex. Also, the interaction of sinensetin with IFNγ did not induce a significant change in the secondary and tertiary structure of the protein. Cellular assays revealed a synergistic effect of sinensetin on IFNγ -triggered anticancer action in HepG2 cells through overexpression of caspase-3 mRNA and protein. In conclusion, this study may hold great promise for the development of potential ligand- protein complexes for therapeutic purposes.

Effect of polysaccharides on conformational changes and functional properties of protein-polyphenol binary complexes: A comparative study

This study aimed to investigate the effect of different polysaccharides on the binding behavior and functional properties of soybean protein isolate (SPI)-quercetin (Que) complex. The binding behavior was assessed using multi-spectral technique with the Stern-Volmer equation, which confirmed the presence of static fluorescence quenching in Que and SPI. The addition of sodium alginate (SA) resulted in a reduction of the binding affinity between SPI and Que, while dextran (DX) exhibited some promoting effect. A slight blue shift was observed in amide I and amide II bands, indicating the presence of hydrophobic and electrostatic interactions. Circular dichroism spectra revealed the ordered structures transformed into a more disordered state when polysaccharides were added, leading to an increase in random coils (SA: 18.5 %, DX: 15.4 %). Docking and dynamic simulations demonstrated that SA displayed greater stability within the hydrophobic compartments of SPI than DX, increased rigidity and stability of the SPI structure in SPI-Que-SA complexes. Electrostatic forces played a significant role between SPI and SA, while van der Waals forces were the main driving forces in SPI-DX complexes. Overall, the introduction of SA led to a looser and stable structure of SPI-Que complexes, resulting in an improvement of their emulsifying, foaming, and antioxidant properties.

Evaluation of substrate specificity and catalytic promiscuity of Bacillus albus cellulase: an insight into in silico proteomic study aiming at enhanced production of renewable energy

Cellulases are enzymes that aid in the hydrolysis of cellulosic fibers and have a wide range of industrial uses. In the present in silico study, sequence alignment between cellulases from different Bacillus species revealed that most of the residues are conserved in those aligned enzymes. Three dimensional structures of cellulase enzymes from 23 different Bacillus species have been predicted and based on the alignment between the modeled structures, those enzymes have been categorized into 7 different groups according to the homology in their conformational folds. There are two structural contents in Gr-I cellulase namely β1-α2 and β3-α5 loops which varies greatly according to their static position. Molecular docking study between the B. albus cellulase and its various cellulosic substrates including xylanoglucan oligosaccharides revealed that residues viz. Phe154, Tyr258, Tyr282, Tyr285, and Tyr376 of B. albus cellulase are significantly involved in formation stacking interaction during enzyme-substrate binding. Residue interaction network and binding energy analysis for the B. albus cellulase with different cellulosic substrates depicted the strong affinity of XylGlc3 substrate with the receptor enzyme. Molecular interaction and molecular dynamics simulation studies exhibited structural stability of enzyme-substrate complexes which are greatly influenced by the presence of catalytic promiscuity in their substrate binding sites. Screening of B. albus in carboxymethylcellulose (CMC) and xylan supplemented agar media revealed the capability of the bacterium in degrading both cellulose and xylan. Overall, the study demonstrated B. albus cellulase as an effective biocatalyst candidate with the potential role of catalytic promiscuity for possible applications in biofuel industries.Communicated by Ramaswamy H. Sarma.

Spectroscopy and dynamics of beta-lactoglobulin complexed with rifampicin

In this paper, we report the binding interaction of milk protein, beta-lactoglobulin (BLG), with an antibiotic against tuberculosis, rifampicin (RIF). BLG intrinsic fluorescence from tryptophan (Trp) amino acids was monitored to understand protein-drug interactions. Binding parameters and stoichiometry were estimated with the help of fluorescence spectral changes. Synchronous fluorescence spectroscopy was employed to exclusively monitor the Trp and Tyrosine (Tyr) environment in the presence of RIF. With the help of steady state fluorescence at different temperatures supported by time-resolved fluorescence, we confirmed that the protein forms a static complex with RIF. Thermodynamic parameters, ΔH and ΔS values, showed the involvement of hydrophobic forces between the RIF and BLG. Competitive displacement assay with ANS confirmed the BLG calyx as the binding site for RIF. Energy transfer mechanism from Trp to RIF was attributed to the fluorescence changes in protein upon complexation. The Förster resonance energy transfer (FRET) was used to find distance, energy transfer efficiency and rate of energy transfer between donor (BLG) and acceptor (RIF). Fourier-transform infrared (FTIR) spectroscopy was utilized for estimating changes in the secondary structure of BLG induced by RIF. Molecular docking was used to visualise the binding location of RIF on BLG. Molecular dynamics (MD) simulation studies showed a consistent binding interactions between BLG and RIF during the 100 ns simulation period and this well supported the increased beta sheet content in FTIR. Overall our results establish the potential of intrinsic fluorescence of BLG in combination with biophysical tools to rationalize drug-protein interactions.Communicated by Ramaswamy H. Sarma.

Compound effect and mechanism of oxidative damage induced by nanoplastics and benzo [a] pyrene

Nanoplastics and polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in soil environments. In order to objectively evaluate the toxic interaction between polystyrene nanoplastics (PS NPs) and benzo [a] pyrene (BaP), oxidative damage at the level of earthworm cells and biomacromolecules was investigated by experiments combined with molecular dynamics simulation. Studies on cells reveal that PS NPs and BaP had synergistic toxicity when it came to causing oxidative stress. Cellular reactive oxygen species (ROS) levels under combined pollutant exposure were 24% and 19% higher, respectively than when PS NPs and BaP were exposed alone (compared to the blank group). In addition, BaP and PS NPs inhibited the ability of CAT to decompose H2O2 by affecting the structure of the proximal amino acid Tyr 357 in the active center of CAT, which exacerbated oxidative stress to a certain extent. Therefore, the synergistic toxic effect of BaP and PS NPs is due to the mutual complement of the two to the induction of protein structural looseness, and the strengthening of the stability of the conjugate (CAT-BaP-PS) under the weak interaction. This work provides a new perspective and approach on how to talk about the toxicity of combined pollutants.

Stepwise changes in flavonoids in spores/pollen contributed to terrestrial adaptation of plants

Protecting haploid pollen and spores against UV-B light and high temperature, 2 major stresses inherent to the terrestrial environment, is critical for plant reproduction and dispersal. Here, we show flavonoids play an indispensable role in this process. First, we identified the flavanone naringenin, which serves to defend against UV-B damage, in the sporopollenin wall of all vascular plants tested. Second, we found that flavonols are present in the spore/pollen protoplasm of all euphyllophyte plants tested and that these flavonols scavenge reactive oxygen species to protect against environmental stresses, particularly heat. Genetic and biochemical analyses showed that these flavonoids are sequentially synthesized in both the tapetum and microspores during pollen ontogeny in Arabidopsis (Arabidopsis thaliana). We show that stepwise increases in the complexity of flavonoids in spores/pollen during plant evolution mirror their progressive adaptation to terrestrial environments. The close relationship between flavonoid complexity and phylogeny and its strong association with pollen survival phenotypes suggest that flavonoids played a central role in the progression of plants from aquatic environments into progressively dry land habitats.

Probing the binding of morin with alpha-2-macroglobulin using multi-spectroscopic and molecular docking approach : Interaction of morin with α2M

Alpha-2-macroglobulin (α2M) is an essential antiproteinase that is widely distributed in human plasma. The present study was aimed at investigating the binding of a potential therapeutic dietary flavonol, morin, with human α2M using a multi-spectroscopic and molecular docking approach. Recently, flavonoid-protein interaction has gained significant attention, because a majority of dietary bioactive components interact with proteins, thereby altering their structure and function. The results of the activity assay exhibited a 48% reduction in the antiproteolytic potential of α2M upon interaction with morin. Fluorescence quenching tests unequivocally confirmed quenching in the fluorescence of α2M in the presence of morin, conforming complex formation and demonstrating that the binding mechanism involves a dynamic mode of interaction. Synchronous fluorescence spectra of α2M with morin showed perturbation in the microenvironment around tryptophan residues. Furthermore, structural changes were observed through CD and FT-IR, showing alterations in the secondary structure of α2M induced by morin. FRET further supports the results of the dynamic mode of quenching. Moderate interaction is shown by binding constant values using Stern-Volmer's fluorescence spectroscopy. Morin binds to α2M at 298 K with a binding constant of 2.7 × 104 M-1, indicating the strength of the association. The α2M-morin system was found to have negative ΔG values, which suggests that the binding process was spontaneous. Molecular docking also reveals the different amino acid residues involved in this binding process, revealing that the binding energy is -8.1 kcal/mol.

Molecular mechanism of green tea polyphenol epicatechin gallate attenuating Staphylococcus aureus pathogenicity by targeting Ser/Thr phosphatase Stp1

In this study, through virtual screening and in vitro bioactivity assays, we discovered that (-)-epicatechin gallate (ECG), a polyphenol compound extracted from green tea, demonstrated marked anti-Ser/Thr phosphatase (Stp1) activity towards Staphylococcus aureus (S. aureus) with an IC₅₀ value of 8.35 μM. By targeting S. aureus Stp1, ECG prevented the up-regulation of virulence gene and the formation of antibody membrane and protected the mice from S. aureus infection. Through MD simulation, the allosteric inhibitory mechanism of ECG on Stp1 was determined. The Stp1-ECG complex model underwent a significant change in conformation; its flap subdomain changed from opening to closing, whereas Stp1 activity was lost when bound to ECG. In addition, the MD simulation results of Stp1 and several tea polyphenol compounds showed that gallate groups and fewer adjacent phenolic hydroxyl groups contributed to the binding of Stp1 and inhibitors. As an inhibitor targeting S. aureus Stp1, ECG reduced the pathogenicity of S. aureus without inhibiting S. aureus, which largely reduced the possibility of drug resistance. Our findings demonstrated a novel molecular mechanism of green tea as the usual drink against S. aureus infection and elucidated the future design of allosteric inhibitors targeting Stp1.

Application of Molecular Simulation Methods in Food Science: Status and Prospects

Molecular simulation methods, such as molecular docking, molecular dynamic (MD) simulation, and quantum chemical (QC) calculation, have become popular as characterization and/or virtual screening tools because they can visually display interaction details that in vitro experiments can not capture and quickly screen bioactive compounds from large databases with millions of molecules. Currently, interdisciplinary research has expanded molecular simulation technology from computer aided drug design (CADD) to food science. More food scientists are supporting their hypotheses/results with this technology. To understand better the use of molecular simulation methods, it is necessary to systematically summarize the latest applications and usage trends of molecular simulation methods in the research field of food science. However, this type of review article is rare. To bridge this gap, we have comprehensively summarized the principle, combination usage, and application of molecular simulation methods in food science. We also analyzed the limitations and future trends and offered valuable strategies with the latest technologies to help food scientists use molecular simulation methods.

A comparative study of the interaction of naringenin with lysozyme by multi-spectroscopic methods, activity comparisons, and molecular modeling procedures

The present study applied steady-state fluorescence, UV-Vis spectrophotometry, molecular docking studies, and circular dichroism (CD) to investigate the interaction of naringenin with lysozyme in an aqueous medium. The UV-Vis measurement indicated the changes in lysozyme secondary and tertiary structure change as a function of the concentration of naringenin. Naringenin could be used to turn the static quenching mechanism into the intrinsic fluorescence of lysozyme. The negative amount of Gibbs free energy (ΔG°) suggested that the binding operation was spontaneous. Fluorescence studies also demonstrated the changes occurring in the Trp microenvironment upon the concatenation into lysozyme. Analysis of thermodynamic parameters also revealed that hydrophobic forces played a fundamental role in determining the complex stability; this was consistent with the previous modeling studies. Circular dichroism also suggested that the alpha-helicity of lysozyme was enhanced as ligand was bound. Naringenin inhibited lysozyme enzymatic activity, displaying its affinity with the lysozyme active site. Further, molecular docking studies demonstrated that naringenin could bind to both residues essential for catalytic activity in the proximity of Trp 62 and Trp 63.

Elucidating the binding mechanism of an antimigraine agent with a model protein: insights from molecular spectroscopic, calorimetric and computational approaches

Sumatriptan (SUM), a serotonin activator used to treat migraines and cluster headaches. Molecular spectroscopic methods including fluorescence quenching, time dependent fluorescence, FRET, absorption, circular dichroism, differential scanning calorimetric and computational approaches were employed to unravel the interaction between sumatriptan and bovine serum albumin (BSA). The fluorescence quenching studies suggested the interaction between SUM and BSA with a moderate binding with the binding constant (K_b) in the order of 10⁴. The findings of temperature and time dependent fluorescence quenching studies confirmed the role of static quenching mechanism. Thermodynamic parameters suggested the key role of electrostatic force in the interaction of SUM with BSA. Absorption and CD spectral studies revealed the bioenvironmental changes around the Trp in BSA upon binding of SUM. Calorimetric based thermal denaturation results confirmed that the thermal stability of BSA was improved in the presence of SUM. resulted in the this decreased flexibility of protein chain. Site competitive studies indicated SUM was located in the hydrophobic cavity of site I which was further confirmed by the docking and dynamic simulation studies. Additionally, molecular dynamics simulations inferred the microenvironmental condition around the SUM and the amino acids and forces involved in the binding of SUM with BSA.Communicated by Ramaswamy H. Sarma.