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The packaging of genomic RNA (gRNA) into retroviral particles relies on the specific recognition by the Gag precursor of packaging signals (Psi), which maintain a complex secondary structure through long-range interactions (LRIs). However, it remains unclear whether the binding of Gag to Psi alone is enough to promote RNA packaging and what role LRIs play in this process. Using mouse mammary tumor virus (MMTV), we investigated the effects of mutations in 4 proposed LRIs on gRNA structure and function. Our findings revealed the presence of an unsuspected extended LRI, and hSHAPE revealed that maintaining a wild-type-like Psi structure is crucial for efficient packaging. Surprisingly, filter-binding assays demonstrated that most mutants, regardless of their packaging capability, exhibited significant binding to Pr77Gag, suggesting that Gag binding to Psi is insufficient for efficient packaging. Footprinting experiments indicated that efficient RNA packaging is promoted when Pr77Gag binds to 2 specific sites within Psi, whereas binding elsewhere in Psi does not lead to efficient packaging. Taken together, our results suggest that the 3D structure of the Psi/Pr77Gag complex regulates the assembly of viral particles around gRNA, enabling effective discrimination against other viral and cellular RNAs that may also bind Gag efficiently., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Prabhu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The retroviral Gag precursor plays a central role in the selection and packaging of viral genomic RNA (gRNA) by binding to virus-specific packaging signal(s) (psi or ψ). Previously, we mapped the feline immunodeficiency virus (FIV) ψ to two discontinuous regions within the 5' end of the gRNA that assumes a higher order structure harboring several structural motifs. To better define the region and structural elements important for gRNA packaging, we methodically investigated these FIV ψ sequences using genetic, biochemical, and structure-function relationship approaches. Our mutational analysis revealed that the unpaired U 85 CUG 88 stretch within FIV ψ is crucial for gRNA encapsidation into nascent virions. High-throughput selective 2' hydroxyl acylation analyzed by primer extension (hSHAPE) performed on wild type (WT) and mutant FIV ψ sequences, with substitutions in the U 85 CUG 88 stretch, revealed that these mutations had limited structural impact and maintained nucleotides 80-92 unpaired, as in the WT structure. Since these mutations dramatically affected packaging, our data suggest that the single-stranded U 85 CUG 88 sequence is important during FIV RNA packaging. Filter-binding assays performed using purified FIV Pr50 Gag on WT and mutant U 85 CUG 88 ψ RNAs led to reduced levels of Pr50 Gag binding to mutant U 85 CUG 88 ψ RNAs, indicating that the U 85 CUG 88 stretch is crucial for ψ RNA-Pr50 Gag interactions. Delineating sequences important for FIV gRNA encapsidation should enhance our understanding of both gRNA packaging and virion assembly, making them potential targets for novel retroviral therapeutic interventions, as well as the development of FIV-based vectors for human gene therapy., (© 2024 Krishnan et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.)

The simian immunodeficiency virus (SIV) precursor polypeptide Pr55 Gag drives viral assembly and facilitates specific recognition and packaging of the SIV genomic RNA (gRNA) into viral particles. While several studies have tried to elucidate the role of SIV Pr55 Gag by expressing its different components independently, studies using full-length SIV Pr55 Gag have not been conducted, primarily due to the unavailability of purified and biologically active full-length SIV Pr55 Gag . We successfully expressed soluble, full-length SIV Pr55 Gag with His 6 -tag in bacteria and purified it using affinity and gel filtration chromatography. In the process, we identified within Gag, a second in-frame start codon downstream of a putative Shine-Dalgarno-like sequence resulting in an additional truncated form of Gag. Synonymously mutating this sequence allowed expression of full-length Gag in its native form. The purified Gag assembled into virus-like particles (VLPs) in vitro in the presence of nucleic acids, revealing its biological functionality. In vivo experiments also confirmed formation of functional VLPs, and quantitative reverse transcriptase PCR demonstrated efficient packaging of SIV gRNA by these VLPs. The methodology we employed ensured the availability of >95% pure, biologically active, full-length SIV Pr55 Gag which should facilitate future studies to understand protein structure and RNA-protein interactions involved during SIV gRNA packaging., Competing Interests: The authors declare no competing interests., (© 2023 The Author(s).)

Simian immunodeficiency virus (SIV) is an important lentivirus used as a non-human primate model to study HIV replication, and pathogenesis of human AIDS, as well as a potential vector for human gene therapy. This study investigated the role of single-stranded purines (ssPurines) as potential genomic RNA (gRNA) packaging determinants in SIV replication. Similar ssPurines have been implicated as important motifs for gRNA packaging in many retroviruses like, HIV-1, MPMV, and MMTV by serving as Gag binding sites during virion assembly. In examining the secondary structure of the SIV 5' leader region, as recently deduced using SHAPE methodology, we identified four specific stretches of ssPurines (I-IV) in the region that harbors major packaging determinants of SIV. The significance of these ssPurine motifs were investigated by mutational analysis coupled with a biologically relevant single round of replication assay. These analyses revealed that while ssPurine II was essential, the others (ssPurines I, III, & IV) did not significantly contribute to SIV gRNA packaging. Any mutation in the ssPurine II, such as its deletion or substitution, or other mutations that caused base pairing of ssPurine II loop resulted in near abrogation of RNA packaging, further substantiating the crucial role of ssPurine II and its looped conformation in SIV gRNA packaging. Structure prediction analysis of these mutants further corroborated the biological results and further revealed that the unpaired nature of ssPurine II is critical for its function during SIV RNA packaging perhaps by enabling it to function as a specific binding site for SIV Gag., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

How retroviral Gag proteins recognize the packaging signals (Psi) on their genomic RNA (gRNA) is a key question that we addressed here using Mason-Pfizer monkey virus (MPMV) as a model system by combining band-shift assays and footprinting experiments. Our data show that Pr78 Gag selects gRNA against spliced viral RNA by simultaneously binding to two single stranded loops on the MPMV Psi RNA: (1) a large purine loop (ssPurines), and (2) a loop which partially overlaps with a mostly base-paired purine repeat (bpPurines) and extends into a GU-rich binding motif. Importantly, this second Gag binding site is located immediately downstream of the major splice donor (mSD) and is thus absent from the spliced viral RNAs. Identifying elements crucial for MPMV gRNA packaging should help in understanding not only the mechanism of virion assembly by retroviruses, but also facilitate construction of safer retroviral vectors for human gene therapy., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Retroviral RNA genome (gRNA) harbors cis-acting sequences that facilitate its specific packaging from a pool of other viral and cellular RNAs by binding with high-affinity to the viral Gag protein during virus assembly. However, the molecular intricacies involved during selective gRNA packaging are poorly understood. Binding and footprinting assays on mouse mammary tumor virus (MMTV) gRNA with purified Pr77Gag along with in cell gRNA packaging study identified two Pr77Gag binding sites constituting critical, non-redundant packaging signals. These included: a purine loop in a bifurcated stem-loop containing the gRNA dimerization initiation site, and the primer binding site (PBS). Despite these sites being present on both unspliced and spliced RNAs, Pr77Gag specifically bound to unspliced RNA, since only that could adopt the native bifurcated stem-loop structure containing looped purines. These results map minimum structural elements required to initiate MMTV gRNA packaging, distinguishing features that are conserved amongst divergent retroviruses from those perhaps unique to MMTV. Unlike purine-rich motifs frequently associated with packaging signals, direct involvement of PBS in gRNA packaging has not been documented in retroviruses. These results enhance our understanding of retroviral gRNA packaging/assembly, making it not only a target for novel therapeutic interventions, but also development of safer gene therapy vectors., (© The Author(s) 2021. Published by Oxford University Press on behalf of Nucleic Acids Research.)

A distinguishing feature of the Mason-Pfizer monkey virus (MPMV) packaging signal RNA secondary structure is a single-stranded purine-rich sequence (ssPurines) in close vicinity to a palindromic stem loop (Pal SL) that functions as MPMV dimerization initiation site (DIS). However, unlike other retroviruses, MPMV contains a partially base-paired repeat sequence of ssPurines (bpPurines) in the adjacent region. Both purine-rich sequences have earlier been proposed to act as potentially redundant Gag binding sites to initiate the process of MPMV genomic RNA (gRNA) packaging. The objective of this study was to investigate the biological significance of ssPurines and bpPurines in MPMV gRNA packaging by systematic mutational and biochemical probing analyses. Deletion of either ssPurines or bpPurines individually had no significant effect on MPMV gRNA packaging, but it was severely compromised when both sequences were deleted simultaneously. Selective 2' hydroxyl acylation analyzed by primer extension (SHAPE) analysis of the mutant RNAs revealed only mild effects on structure by deletion of either ssPurines or bpPurines, while the structure was dramatically affected by the two simultaneous deletions. This suggests that ssPurines and bpPurines play a redundant role in MPMV gRNA packaging, probably as Gag binding sites to facilitate gRNA capture and encapsidation. Interestingly, the deletion of bpPurines revealed an additional severe defect on RNA propagation that was independent of the presence or absence of ssPurines or the gRNA structure of the region. These findings further suggest that the bpPurines play an additional role in the early steps of MPMV replication cycle that is yet to be identified., (Copyright © 2020 Ali, Pitchai, Vivet-Boudou, Chameettachal, Jabeen, Pillai, Mustafa, Marquet and Rizvi.)

The feline immunodeficiency virus (FIV) full-length Pr50 Gag precursor is a key player in the assembly of new viral particles. It is also a critical component of the efficient selection and packaging of two copies of genomic RNA (gRNA) into the newly formed virus particles from a wide pool of cellular and spliced viral RNA. To understand the molecular mechanisms involved during FIV gRNA packaging, we expressed the His 6 -tagged and untagged recombinant FIV Pr50 Gag protein both in eukaryotic and prokaryotic cells. The recombinant Pr50 Gag -His 6 -tag fusion protein was purified from soluble fractions of prokaryotic cultures using immobilized metal affinity chromatography (IMAC). This purified protein was able to assemble in vitro into virus-like particles (VLPs), indicating that it preserved its ability to oligomerize/multimerize. Furthermore, VLPs formed in eukaryotic cells by the FIV full-length Pr50 Gag both in the presence and absence of His 6 -tag could package FIV sub-genomic RNA to similar levels, suggesting that the biological activity of the recombinant full-length Pr50 Gag fusion protein was retained in the presence of His 6 -tag at the carboxy terminus. Successful expression and purification of a biologically active, recombinant full-length Pr50 Gag -His 6 -tag fusion protein will allow study of the intricate RNA-protein interactions involved during FIV gRNA encapsidation.

The Mason-Pfizer monkey virus (MPMV) genomic RNA (gRNA) packaging signal is a highly-structured element with several stem-loops held together by two phylogenetically conserved long-range interactions (LRIs) between U5 and gag complementary sequences. These LRIs play a critical role in maintaining the structure of the 5´ end of the MPMV gRNA. Thus, one could hypothesize that the overall RNA secondary structure of this region is further architecturally held together by three other stem loops (SL3, Gag SL1, and Gag SL2) comprising of sequences from the distal parts of the 5´untranslated region (5' UTR) to ~ 120 nucleotides into gag, excluding gag sequences involved in forming the U5-Gag LRIs. To provide functional evidence for the biological significance of these stem loops during gRNA encapsidation, these structural motifs were mutated and their effects on MPMV RNA packaging and propagation were tested in a single round trans-complementation assay. The mutant RNA structures were further studied by high throughput SHAPE (hSHAPE) assay. Our results reveal that sequences involved in forming these three stem loops do not play crucial roles at an individual level during MPMV gRNA packaging or propagation. Further structure-function analysis indicates that the U5-Gag LRIs have a more important architectural role in stabilizing the higher order structure of the 5´ UTR than the three stem loops which have a more secondary and perhaps indirect role in stabilizing the overall RNA secondary structure of the region. Our work provides a better understanding of the molecular interactions that take place during MPMV gRNA packaging.

MPMV precursor polypeptide Pr78 Gag orchestrates assembly and packaging of genomic RNA (gRNA) into virus particles. Therefore, we have expressed recombinant full-length Pr78 Gag either with or without His 6 -tag in bacterial as well as eukaryotic cultures and purified the recombinant protein from soluble fractions of the bacterial cultures. The recombinant Pr78 Gag protein has the intrinsic ability to assemble in vitro to form virus like particles (VLPs). Consistent with this observation, the recombinant protein could form VLPs in both prokaryotes and eukaryotes. VLPs formed in eukaryotic cells by recombinant Pr78 Gag with or without His 6 -tag can encapsidate MPMV transfer vector RNA, suggesting that the inclusion of the His 6 -tag to the full-length Pr78 Gag did not interfere with its expression or biological function. This study demonstrates the expression and purification of a biologically active, recombinant Pr78 Gag , which should pave the way to study RNA-protein interactions involved in the MPMV gRNA packaging process.

The mouse mammary tumor virus (MMTV) Pr77 Gag polypeptide is an essential retroviral structural protein without which infectious viral particles cannot be formed. This process requires specific recognition and packaging of dimerized genomic RNA (gRNA) by Gag during virus assembly. Most of the previous work on retroviral assembly has used either the nucleocapsid portion of Gag, or other truncated Gag derivatives—not the natural substrate for virus assembly. In order to understand the molecular mechanism of MMTV gRNA packaging process, we expressed and purified full-length recombinant Pr77 Gag -His₆-tag fusion protein from soluble fractions of bacterial cultures. We show that the purified Pr77 Gag -His₆-tag protein retained the ability to assemble virus-like particles (VLPs) in vitro with morphologically similar immature intracellular particles. The recombinant proteins (with and without His₆-tag) could both be expressed in prokaryotic and eukaryotic cells and had the ability to form VLPs in vivo. Most importantly, the recombinant Pr77 Gag -His₆-tag fusion proteins capable of making VLPs in eukaryotic cells were competent for packaging sub-genomic MMTV RNAs. The successful expression and purification of a biologically active, full-length MMTV Pr77 Gag should lay down the foundation towards performing RNA–protein interaction(s), especially for structure-function studies and towards understanding molecular intricacies during MMTV gRNA packaging and assembly processes.

Flocculation of kaolinite using chitosan alone as flocculant has been reported to be difficult. Detailed investigations in our laboratory have shown that kaolinite can be easily removed from aqueous suspensions by flocculation and settling using chitosan, provided the suspension medium contains traces of dissolved humic substances. The flocculation is also extremely sensitive to the pH of the suspension. Removal of suspended titanium dioxide particles in water by flocculation using chitosan in presence of humic acids is also reported for the first time. A plausible mechanism explaining these observations is proposed in this paper.

Retro-ACP (74-65) fragment was synthesized on a novel 4% tri-(propylene glycol) glycerolate diacrylate cross-linked polystyrene (PS-TRPGGDA) support. The peptide is grown from the functional site present in the cross-linker, which makes it unique and cost-effective among other styrene based polymer supports. A comparative study with Merrifield resin indicates high yield and purity of the peptide synthesized on the novel support.

A highly flexible, mechanically and chemically stable copolymer, tri(propylene glycol) glycerolate diacrylate cross-linked polystyrene (PS-TRPGGDA), was synthesized by the suspension polymerization and employed as a solid support for peptide synthesis. The beaded polymer support containing secondary hydroxyl functional groups in the cross-linker was used as the growth site for peptide synthesis. The procedure is unique and cost-effective in that it avoids the initial functionalization steps required for most of the styrene-based polymer supports. The resin was characterized by 13C-CP-MAS NMR spectroscopy and the morphologic features of the resin were investigated using scanning electron microscopy. Swelling studies conducted on the new support revealed that the PS-TRPGGDA resin undergoes more effective swelling and solvation than PS-DVB resin in all solvents used in peptide synthesis. The efficiency of the new support was demonstrated by synthesizing a 'difficult' sequence Ala-Arg-(Ala)6-Lys and comparing it with commercially available Merrifield and Sheppard resins. The synthetic efficiency was further demonstrated by the synthesis of a 24-residue NR 2A peptide substrate of calcium/calmodulin-binding peptide. The high yield and purity of the peptide synthesized on the novel support indicates the positive role of the flexible and hydrophilic cross-linking agent in the solid support.

Three peptide fragments selected from the NS-1 region of hepatitis C-viral polyprotein (Leu-Ile-Asn-Thr-Asn-Ala-Ser-Trp-His-Ala-Asn-Arg-Thr-Ala-Leu-Ser Asn-Asp Ser-Lys Leu Asn Thr-Gly Ala NH(2), Leu-lle Asn Thr Asn Ala Ser-Trp-His-Ala-Asn-Arg-Thr Ala NH(2) and Leu-Asn-Cys(Acm)-Asn-Asp-Ser-Leu-Asn-Thr-Ala-NH(2)) have been synthesized on PS-BDODMA resin. The synthetic capability of the resin PS-BDODMA resin was compared with Merrifield resin. The peptides were synthesized by the stepwise fluoren-9-yl methoxycarbonyl (Fmoc) solid-phase method. The synthesized peptides were purified by HPLC and the identity of the peptides was established by mass spectrum and amino acid analysis. The synthesis of these peptides illustrates the application of the PS-BDODMA resin for the synthesis of long chain peptides in high yield and homogeneity compared to the Merrifield resin.

Flocculation of silt in river water using chitosan was studied in the pH range 4-9, and suspended solid concentrations in the range 20-80 mg/L. Chitosan effectively reduces turbidity due to silt by flocculation and settling. Flocculation efficiency is very sensitive to pH, and reaches a maximum at pH 7. The optimal chitosan concentration required to effect flocculation is 0.5 mg/L and is independent of silt concentration within the range examined. Restabilisation of the suspension is observed at higher concentrations of chitosan, and the amount required for restabilisation increases with increasing concentration of suspended solids. Flocculation is faster at higher concentrations of silt and the flocs are large and fibrous.

A highly solvating copolymer was prepared in high yield by introducing a flexible crosslinker, 1,4-butanedioldimethacrylate, into the polystyrene matrix by a free radical aqueous suspension polymerization. A 2 mol% crosslinked resin showed rigidity and mechanical characteristics comparable to those of divinylbenzene-crosslinked polystyrene (Merrifield resin, DVB-PS) support. Swelling and solvation characteristics of the new resin, BDDMA-PS, were much higher than DVB-PS support in all solvents used for solid phase peptide synthesis. The diacrylate crosslinks in the resin network were found to be highly stable even after 48 h treatment with neat TFA, 6 N HCl and 6 N KOH at 110 degrees C. To demonstrate the usefulness of the new resin in high capacity peptide synthesis, a typical difficult peptide, acyl carrier protein (ACP) fragment (65-74), was synthesized on commercially available 1 mol% crosslinked DVB-PS and 2 mol% crosslinked BDDMA-PS resins under identical conditions. A protocol using NMP/DMSO mediated coupling was employed for chain assembly. The yield and purity of the product from BDDMA-PS resin was higher than when the DVB-PS resin was used. The mechanistic reason behind the synthetic efficiency of the new resin was found to be its ability to induce random coil conformation to the growing peptide chains.

Flocculation of kaolinite suspensions in water using chitosan was studied in the pH range 5-9 and the turbidity ranging from 10 to 160 NTU. Chitosan, in presence of trace quantities of a substance present in aqueous soil extracts, effectively reduces turbidity due to kaolinite by flocculation and settling. Flocculation efficiency is very sensitive to pH, and reaches a maximum at pH 7.5. The optimal chitosan concentration required to effect flocculation is independent of kaolinite concentration within the range examined. Flocculation is faster at higher concentrations of kaolinite and the flocs are large and settle rapidly.

Peptides were synthesized with very high purity and yield on a highly solvating copolymer of 1,4-butanediol dimethacrylate cross-linked polystyrene support (PS-BDODMA). The polymer was synthesized by radical aqueous suspension polymerization using toluene as the diluent and 1% polyvinyl alcohol as the suspension stabilizer. The supports were highly resistant to various chemical reagents and solvents that are frequently used in polypeptide synthesis. The peptides synthesized on this support were designed from the core (C), envelope (E1 and E2) and nonstructural protein (NS1-NS5) regions of the prototype hepatitis C viral (HCV) polyprotein, and were used to develop a peptide-based immunoassay (PBEIA) for the detection of HCV antibodies. The purity of these peptides was tested by HPLC. Peptide identity was confirmed by amino acid analysis and MALDI-TOF-MS. A single peptide chosen from a conserved area (E2/NS1) at the C-terminus of the hypervariable region (HVRI) was found to be sufficient for effective and reliable diagnosis of HCV infection in infected individuals, as well as also apparently healthy individuals. The CD spectrum of the peptide shows no preference for any ordered secondary structure. When used, peptide mixtures from various protein regions of HCV reduced the sensitivity and reliability of the diagnosis partly because of epitope masking.

Peptide segments corresponding to antibacterial esculentin-1 (1-15), (3344), (9-27), and their modified forms were synthesized on 1,4-butanediol dimethacrylate cross-linked polystyrene (PS-BDODMA) support. Hydroxymethyl and aminomethyl 2% PS-BDODMA supports were used for the synthesis. The HMPB linker was appended to the aminomethyl resin using HBTU in presence of HOBt and the first amino acid was incorporated using MSNT. The conventional Fmoc synthetic protocol was used for the synthesis of peptides. The peptides were cleaved from the support using TFA. The peptides were purified by HPLC, and characterized by amino acid analysis and MALDI TOF MS. The secondary structures of the peptides were revealed by CD measurements. The synthesis of these peptides illustrates the utility of the new support for the synthesis of long-chain bioactive peptides. The synthetic peptides were tested for antimicrobial activity against Escherichia coli Mos blue, E. coli 2, Bacillus brevis, B. megaterium, Pseudomonas HTL, and Vibrio mimicus. The antibacterial activity of the peptides was explained on the basis of the helicity and charged nature of the sequences.

Four peptides were designed and synthesized on a highly solvating copolymer of tetraethyleneglycol diacrylate cross-linked polystyrene (PS-TTEGDA) support with very high purity and yield. The polymer was synthesized in various cross-linking densities (1, 2, 3, 4, 5 and 10%) using radical aqueous suspension polymerization. Four per cent PS-TTEGDA resin showed rigidity and mechanical characteristics comparable with those of divinylbenzene cross-linked polystyrene (PS-DVB) support. Swelling and solvation characteristics of PS-TTEGDA were much higher than PS-DVB support in all solvents used in solid-phase peptide synthesis. Forty-eight hour treatment of the support with neat trifluoroacetic acid did not show any change in its infrared spectra. PS-TTEGDA could be functionalized with chloromethyl, aminomethyl and hydroxymethyl functional groups under various controlled conditions. Synthetic utility of the support was demonstrated by the synthesis of four peptides selected from the envelope and nonstructural protein region of the prototype hepatitis C virus (HCV). These peptides were later used successfully to develop a peptide-based immunoassay (PBEIA) for the detection of HCV immunity. Peptides designed from the NS1 and NS4 protein regions were found to be very promising for the development of a new diagnostic kit to detect HCV infection in human blood. Peptide purity was tested by RP-FPLC and the peptide identity was confirmed by amino acid analysis.

A novel 1,6-hexanediol diacrylate cross-linked resin was prepared that was subsequently functionalized by using chloromethyl methyl ether to afford a high-capacity resin. The resin exhibited good swelling and its application in the successful synthesis of a 13-residue peptide corresponding to the fragment of seminalplasmin has been illustrated. The resin was chemically inert at peptide synthetic conditions.

The synthesis of three hydrophobic peptides, which are partial sequences of thioredoxin, on a newly developed, flexible 1,6-hexanediol diacrylate cross-linked polystyrene, in good yield and purity, is described.

The continued and rapid discoveries of new peptides with interesting biological functions have created an unprecedented demand for the chemical synthesis of peptides required for structure-function correlations. Several strategic improvements have been suggested and tested to meet the demand for peptides in high purity and quantity. This article describes the synthesis of three partial sequences of thioredoxin, a naturally occurring sulfur-reducing protein containing 108 amino acid residues, on a newly developed flexible, cross-linked polystyrene support (2% polystyrene cross-linked with 1,6-hexanediol diacrylate) using the standard solid-phase methodology. The protected peptides were cleaved from the polymeric support by trifluoroacetic acid and purified by chromatography. The free peptides were shown to be homogeneous by high-performance liquid chromatography and were characterized by amino acid analysis and circular dichroism. The circular dichroism measurement revealed that the peptides possess a helical conformation. From the yield and purity of the peptides obtained, it was inferred that the favorable swelling and solvation characteristics of the support facilitated effective synthesis.

A 13-residue peptide corresponding to a hydrophobic segment of the antimicrobial 47-residue peptide seminalplasmin, PKLLETFLSKWIG (SPF), has been shown to have antibacterial and hemolytic activities (N. Sitaram and R. Nagaraj, J. Biol. Chem. 265:10438-10442, 1990). In an effort to get an insight into the structural and charge requirements for these biological activities, an analog of SPF in which Glu has been replaced with Lys has been synthesized and its antibacterial and hemolytic properties have been examined. It has been demonstrated that the analog, SPFK, exhibits potent antibacterial activity at concentrations at which hemolysis does not occur.

A chelating ion-exchange resin with hydroxamic acid functional groups was synthesized from styrene-maleic acid co-polymer cross-linked with divinylbenzene. A resin prepared from equimolar amounts of styrene and maleic anhydride with 0.75 mole% divinylbenzene gives the best sorption characteristics. The selectivity of the resin for metal ions is copper(II) > cobalt(II) > zinc(II) > nickel(II) > manganese(II) > chromium(III) > iron(III) > vanadium(V). Copper(II), chromium(III) and iron(III) in chromium plating baths can be separated by use of the resin and determined spectrophotometrically.

A chelating resin containing a stable thiol group was synthesised, using polystyrene as the starting material. The resin is stable towards conc. HCl, 0.1M HNO(3) and 0.1M NaOH. The resin shows affinity towards Ag(+), Hg(2+), Bi(3+), Pb(2+), Cu(2+), Zn(2+) and Cd(2+). Extraction of these metal ions as a function of pH, kinetics of exchange and breakthrough capacities is evaluated. The selectivity of the resin for the metal ions is in the order Ag(+) > Hg2+ > Cu2+ > Pb2+ > Cd2+ > Zn2+. The equilibrium constants for exchange and kinetics of exchange are favourable for the recovery of mercury from lean sources. Application of the resin in the stripping of mercury from chlor-alkali plant affluent, and in the enrichment of mercury from seawater, have been investigated. Mercury sorbed resin can be regenerated using 5% thiourea in 0.1M HCl.

A stable new redox titrant, viz., iodosobenzene diacetate in anhydrous acetic acid medium, is proposed for the potentiometric determination of a number of reductants such as As(III), I(-), Fe(II), N(2)H(4), [Fe(CN)(6)](4-), Tl(I), Sb(III), hydroquinone, ascorbic acid, phenol, aniline and oxine.