Selective and sensitive determination of peptides using 3,4-dihydroxyphenylacetic acid as a fluorogenic reagent

Fluorometric assay for phenotypic differentiation of drug-resistant HIV mutants

Convenient drug-resistance testing of viral mutants is indispensable to effective treatment of viral infection. We developed a novel fluorometric assay for phenotypic differentiation of drug-resistant mutants of human immunodeficiency virus-I protease (HIV-PR) which uses enzymatic and peptide-specific fluorescence (FL) reactions and high-performance liquid chromatography (HPLC) of three HIV-PR substrates. This assay protocol enables use of non-purified enzyme sources and multiple substrates for the enzymatic reaction. In this study, susceptibility of HIV mutations to drugs was evaluated by selective formation of three FL products after the enzymatic HIV-PR reaction. This proof-of-concept study indicates that the present HPLC-FL method could be an alternative to current phenotypic assays for the evaluation of HIV drug resistance.

Amplified and selective assay of collagens by enzymatic and fluorescent reactions

Sensitive and selective assay of collagen is of substantial importance to the diagnostic study of health- and aging-related failures. In this paper, we describe a highly specific and sensitive method for the assay of whole collagens in biological samples using a novel fluorogenic reagent, 3,4-dihydroxyphenylacetic acid (3,4-DHPAA). The 3,4-DHPAA reagent can selectively detect N-terminal Gly-containing peptides (NGPs) in the presence of sodium borate and NaIO4. Under conditions optimized, this assay format for collagen, termed 3,4-DHPAA assay method showed a good linear relationship between the amplified FL signals and the collagen concentrations from 0.18 to 12 μg/ml. Therefore the sensitive determination of intracellular collagens in cheek tissue and HeLa cells was individually possible without any separation protocol. The dual recognitions of the collagens in the samples could be performed by the enzymatic digestion and the FL reaction. The proposed assay method enables the determination facile, specific, sensitive and quantitative for biogenic collagens.

A novel fluorescence reaction for N-terminal Ser-containing peptides and its application to assay caspase activity

Caspases are the key regulatory factors of apoptosis and are also found to be involved in inflammatory cytokinesis. Sensitive and selective determination of caspases has significant importance in evaluation of apoptosis, disease diagnosis, and drug development. Here, we developed an assay method for the determination of caspase activity. This method is based on a novel fluorescence (FL) reaction selective for N-terminal Ser-containing peptides. FL derivatization of peptides requires heating in the presence of catechol, HEPES buffer (pH 7.5), and sodium periodate. Under optimized conditions, the reaction showed a unique sequence preference for N-terminal Ser-containing peptides, and a lower detection limit (signal/noise [S/N] = 3) of approximately 0.1 μM was obtained for SKTS and SSNSF. Acetylated substrates were enzymatically cleaved to produce N-terminal Ser-containing peptides, which were selectively converted to FL compounds. The enzyme activities were simultaneously determined as low as 2 U (4.3 nM) caspase-3 and 2.5 U (3.3 nM) caspase-8 by high-performance liquid chromatography (HPLC) with FL detection. The proposed assay method does not require any labeled substrates and can be applied to evaluate cell-based apoptosis and also to study apoptosis inhibitors or inducers.