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Graphene oxide (GO) is an emerging luminescent nanomaterial with photostable and unique photoluminescence (PL) in the visible and near-infrared region. Herein, a GO PL-based optical biosensor consisting of a luminescent GO donor covalently linked with a peptide-quencher complex is reported for the simple, rapid, and sensitive detection of proteases. To this end, the quenching efficiency of various candidate quenchers of GO fluorescence, such as metalloprotoporphyrins and QXL570, are examined and their quenching mechanisms investigated. A fluorescence resonance energy transfer-based quencher, QXL570, is found to be much more effective for quenching the intrinsic fluorescence of GO than other charge transfer-based quenchers. The designed GO-peptide-QXL system is then able to sensitively detect specific proteases-chymotrypsin and matrix metalloproteinase-2-via a 'turn-on' response of quenched GO fluorescence after proteolytic cleavage of the quencher. Finally, the GO-peptide-QXL hybrid successfully detects MMP-2 secreted from living cells-human hepatocytes HepG2-with high sensitivity. [ABSTRACT FROM AUTHOR]

ABSTRACT Conjugation of an oligopeptide or an amino acid to bioactive compounds is one of the simplest chemical modifications to modulate the biological functions of the compounds. Recently, numerous methods have been proposed for the modification of their properties, including the alteration of their chemical and physical properties, and of their original bioactivities. We review the current knowledge of the adaptability of oligopeptide or amino acid conjugation for modulating the biological activities of biomolecules. © 2013 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 584-591, 2013. [ABSTRACT FROM AUTHOR]

Tyrosinase plays a critical role in the early stages of the melanin synthetic pathway by catalyzing the oxidation of the substrate. Therefore, tyrosinase inhibitors have been intensively studied in both cosmetic and food industries to develop hypopigmentary agents and prevent enzymatic browning in food. Previously, we reported that kojic acid-amino acid amide (KA-AA-NH2) showed enhanced tyrosinase inhibitory activity compared with kojic acid alone, but this was not observed in a cell test because of poor cell permeability. To enhance cell permeability, we prepared copper and zinc complexes of KA-AA-NH2 and characterized them using FT-IR spectroscopy, ESI-MS spectrometry, and inductively coupled plasma analysis. We then showed that KA-AA-NH2 copper complexes exhibited melanogenesis inhibitory activity in Mel-Ab cells. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Antioxidants have become an important subject of study as an active ingredient for cosmetics and preservatives for food. We synthesized antioxidative peptide conjugates of hydroxycinnamic acids (HCAs) such as ferulic acid (FA), caffeic acid (CA), and sinapic acid (SA) by SPPS method. We measured their potential antioxidant properties by 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging test and lipid autoxidation inhibition test. When the antioxidative peptides, such as glutathione analogue (GS(Bzl)H) and carnosine (CAR), were conjugated to HCAs, their antioxidative activities were enhanced significantly. CA-peptides exhibited the highest free radical scavenging activity by the DPPH test, and showed good antioxidative activity in the lipid autoxidation test. FA- and SA-peptides showed excellent antioxidative activity in the lipid autoxidation test. Furthermore, we demonstrated a synergistic antioxidative activity of HCA-peptide conjugates by comparing their antioxidative activity with that of a simple mixture of HCAs and the antioxidant peptides. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]