Search PubMed⌕ Search

Biomedical subjects

N S Agarwal

Publications and source records attributed to N S Agarwal.

8 recordsLinked to original sources
PubMed1999

Retina-derived fetuin (RDF): analysis by immunocytochemistry, reverse transcriptase-polymerase chain reaction and Southern blot.

PURPOSE: This study was undertaken to determine the presence of retina-derived fetuin (RDF) protein and its message in retinal tissues and retinal pigment epithelial (RPE) cells. The techniques utilized in this study included light micros-copy, immunochemistry, Western blot, reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot. METHODS: Retinal tissues and sections from embryonic, early postnatal and adult normal rats and retinal pigment epithe-lial (RPE) cells from postnatal rats were immunostained for fetuin with a polyclonal fetuin antibody and a peroxidase conjugated-secondary antibody using immunocytochemistry and Western blot analyses. The cDNA generated from RNA isolated from early postnatal rat retinas and RPE was probed with primers for rat fetuin, amplified by PCR and the PCR products were analyzed by Southern blot. RESULTS: Fetuin (RDF) was immunolocalized to cells of the neuroepithelium in retinas of early postnatal rats and most prominently in the nuclei and perinuclear region of cultured neonatal rat RPE cells. In adult retinas, ganglion cells, inner segments of photoreceptor cells, some components of the outer plexiform layer, ganglion cells and optic nerve processes were immunoreactive for the fetuin protein. As shown by Western blot, fetuin (RDF) was higher in embryonic and early postnatal retinas than in late postnatal retinas, indicating that this protein may be developmentally regulated. Using RT-PCR, the message for rat fetuin was demonstrated in the retina and RPE of normal postnatal rats. Southern blot confirmed that the PCR product from the retina and RPE was generated from rat fetuin mRNA as well as from rat liver, the primary source of fetuin. CONCLUSIONS: Fetuin, termed retina-derived fetuin (RDF), is reported for the first time in retinal tissues. Fetuin is a cysteine protease inhibitor that may play a role in support of neuronal cell survival during early retinal development and the maintenance of neuronal activity. RDF may interact with other growth factors and cytokines in providing trophic support for neurons and possibly other cells of the developing retina.

Animals↗
PubMed1986

Inhibition of cathepsin D by substrate analogues containing statine and by analogues of pepstatin.

Five new cathepsin D inhibitors were synthesized and tested as inhibitors of bovine cathepsin D. The compounds were derived by replacing a Phe-Phe dipeptidyl unit of a good cathepsin D substrate, Boc-Phe-Leu-Ala-Phe-Phe-Val-Leu-OR, with statine [3S,4S)-4-amino-3-hydroxy-6-methylheptanoic acid, Sta) or with Sta-Phe. The best inhibitor, Boc-Phe-Leu-Ala-(S,S)-Sta-Val-Leu-OMe, inhibited cathepsin D with a Ki value of 1.1 nM. In general, the more effective inhibitors were consistent with the proposal that statine functions as a replacement for a dipeptidyl unit. Thirty-five known pepstatin analogues also were evaluated as cathepsin D inhibitors. Substituents in the P4 and P3' positions are important for maximal inhibition of this aspartic proteinase, and the P4 substituent appears more important for inhibition of cathepsin D than for inhibition of other aspartic proteinases.

Amino Acid Sequence↗
PubMed1985

Inhibition of aspartic proteases by pepstatin and 3-methylstatine derivatives of pepstatin. Evidence for collected-substrate enzyme inhibition.

The synthesis of 10 analogues of pepstatin modified so that statine is replaced by 4-amino-3-hydroxy-3,6-dimethylheptanoic acid (Me3Sta) or 4-amino-3-hydroxy-3-methyl-5-phenylpentanoic acid (Me3AHPPA) residues is reported. Both the 3S,4S and 3R,4S diastereomers of each analogue were tested as inhibitors of the aspartic proteases, porcine pepsin, cathepsin D, and penicillopepsin. In all cases the 3R,4S diastereomer (rather than the 3S,4S diastereomer) of the Me3Sta and Me3AHPPA derivatives was found to be the more potent inhibitor of the aspartic protease (Ki = 1.5-10 nM for the best inhibitors), in contrast to the results obtained with statine (Sta) or AHPPA derivatives, where the 3S,4S diastereomer is the more potent inhibitor for each diastereomeric pair of analogues. The Me3Sta- and Me3AHPPA-containing analogues are only about 10-fold less potent than the corresponding statine and AHPPA analogues and 100-1000-fold more potent than the corresponding inhibitors lacking the C-3 hydroxyl group. Difference NMR spectroscopy indicates that the (3R,4S)-Me3Sta derivative induces conformational changes in porcine pepsin comparable to those induced by the binding of pepstatin and that the (3S,4S)-Me3Sta derivatives do not induce the difference NMR spectrum. These results require that the C-3 methylated analogues of statine-containing peptides must inhibit enzymes by a different mechanism than the corresponding statine peptides. It is proposed that pepstatin and (3S)-statine-containing peptides inhibit aspartic proteases by a collected-substrate inhibition mechanism. The enzyme-inhibitor complex is stabilized, relative to pepstatin analogues lacking the C-3 hydroxyl groups, by the favorable entropy derived when enzyme-bound water is returned to bulk solvent.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspartic Acid Endopeptidases↗
PubMed1981

Glucagon structure-function relationships using isolated rat hepatocytes.

The ability of glucagon and several of its semi-synthetic analogues to stimulate glucose production in isolated rat hepatocytes was measured and compared for relative potencies. The order of decreasing biological activities of glucagon in this assay was as follows: glucagon greater than [HArg12]-glucagon greater than [des-Asn28, Thr29][homoserinehydrazide27]-glucagon approx. equal to [des-His1]-glucagon greater than [des-Asn28, Thr29][homoserinelactone27]-glucagon greater than [des-Asn28, Thr29]-[n-butylhomoserineamide27]-glucagon greater than glucagon1-21. Qualitatively, these results are similar to those obtained previously in the hepatic plasma membrane adenylate cyclase assay. Minor exceptions were noted for the hydrazide derivative and the partial agonist [des-His1]-glucagon, both of which were slightly more potent relative to glucagon in the glycogenolytic assay than in the adenylate cyclase assay. The assay provides important insight into glucagon structure-function relationships.

Amino Acid Sequence↗
PubMed1980

Synthesis of protected secretin 16-27 on a Merrifield resin. Examination of ammonolysis conditions for preparing carboxamide terminal protected peptides suitable for fragment condensation.

The partially protected dodecapeptide to secretin, H-Ser(Bzl)-Ala-Arg(Tos)-Leu-Gln-Arg(Tos)-Leu-Leu-Gln-Gly-Leu-Val-NH2 (protected secretin 16-27) was prepared using a standard Merrifield resin and solid phase synthesis methods. For comparative purposes the unprotected peptide also was prepared on a benz-hydrylamine resin. Contrary to previous reports, the valine C-terminal peptide can be cleaved from the resin and the amide obtained in high yield. A variety of conditions were examined to accomplish the cleavage of the peptide from the resin in its carboxamide terminal form. The best conditions found were trans-esterification followed by ammonolysis in a mixed solvent system. A thin-layer chromatography system which clearly separates the methyl ester and carboxamide terminal secretin 16-27 was developed.

Amino Acid Sequence↗