Angiogenin (Ang), is a ribonucleolytic protein that is associated with angiogenesis, the formation of blood vessels. The involvement of Ang in vascularisation makes it a potential target for the identification of compounds that have the potential to inhibit the process. The compounds may be assessed for their ability to inhibit the ribonucleolytic activity of the protein and subsequently blood vessel formation, a crucial requirement for tumor formation. We report an inhibition of the ribonucleolytic activity of Ang with the gallate containing green tea polyphenols, ECG and EGCG that exhibits an increased efficacy upon forming polyphenol-capped gold nanoparticles (ECG-AuNPs and EGCG-AuNPs). The extent of inhibition was confirmed using an agarose gel-based assay followed by fluorescence titration studies that indicated a hundred fold stronger binding of polyphenol-capped gold nanoparticles (GTP-AuNPs) compared to the bare polyphenols. Interestingly, we found a change in the mode of inhibition from a noncompetitive type to a competitive mode of inhibition in case of the GTP-AuNPs, which is in agreement with the 'n' values obtained from the fluorescence quenching studies. The effect on angiogenesis has also been assessed by the chorioallantoic membrane (CAM) assay. We find an increase in the inhibition potency of GTP-AuNPs that could find applications in the development of anti-angiogenic compounds.

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Protein nitration can occur as ar esult of peroxynitrite-mediated oxidative stress. Excess production of peroxynitrite (PN) within the cellular mediumc an cause oxidative damage to biomolecules.T he in vitro nitration of Ribonuclease A( RNase A) resultsi nn itrotyrosine (NT) formation with as trong dependence on the pH of the medium. In order to mimic the cellular environment in this study,P Nmediated RNase An itration has been carried out in ac rowd-ed medium. The degree of nitration is higher at pH 7.4 (physiological pH) compared to pH 6.0 (tumorc ell pH). The extent of nitration increases significantly when PN is added to RNase Ai nt he presence of crowding agentsP EG 400 and PEG 6000. PEG has been found to stabilize PN overaprolonged period,t hereby increasing the degree of nitration. NT formation in RNase Aa lso results in as ignificant loss in enzymatic activity.Scheme1.Generation of peroxynitrite and subsequent formation of nitrating species.

Flavonoids are a class of polyphenols that possess diverse properties. The structure‐activity relationship of certain flavonoids and resveratrol with ribonuclease A (RNase A) has been investigated. The selected flavonoids have a similar skeleton and the positional preferences of the phenolic moieties toward inhibition of the catalytic activity of RNase A have been studied. The results obtained for RNase A inhibition by flavonoids suggest that the planarity of the molecules is necessary for effective inhibitory potency. Agarose gel electrophoresis and precipitation assay experiments along with kinetic studies reveal Ki values for the various flavonoids in the micromolar range. Minor secondary structural changes of RNase A were observed after interaction with the flavonoids. An insight into the specific amino acid involvement in the binding of the substrate using docking studies is also presented. The dipole moment of the flavonoids that depends on the orientation of the hydroxyl groups in the molecule bears direct correlation with the inhibitory potency against RNase A. The direct association of this molecular property with enzyme inhibition can be exploited for the design and development of inhibitors of proteins.

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