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R Leduc

Publications and source records attributed to R Leduc.

60 records · Page 4Linked to original sources
PubMed1978

High-pressure liquid chromatographic analysis of carbofuran and two non-conjugated metabolites in crops as fluorescent dansyl derivatives.

Carbofuran, and non-conjugated 3-hydroxycarbofuran and 3-ketocarbofuran were extracted from carrots, corn and potatoes with acetone and partitioned into hexane-methylene chloride. The organic extract was evaporated to a small volume for clean-up on a 2% deactivated Florisil column. All three carbamates were eluted with 15% acetone in hexane. The pesticide residues were hydrolysed to their corresponding phenols with 0.1 M sodium carbonate followed by derivatization with dansyl chloride in acetone. The derivatives were extracted and analysed by high-pressure liquid chromatography with fluorescence detection (excitation, 360 nm; emission, greater than 400 nm). Absolute recoveries for all three compounds were between 50 and 65% for spiked samples by the extraction method used. Detection limits approached 0.01 ppm in the foods studied.

Carbofuran↗
PubMed1978

High pressure liquid chromatography with ultraviolet absorbance or fluorescence detection of carbaryl in potato and corn.

Carbaryl (1-naphthyl-N-methylcarbamate) was extracted from corn and potato with acetone. The acetone extract was partitioned into methylene chloride-hexane and concentrated for cleanup on a 5% water-deactivated Florisil column. The fraction containing the carbamate was subjected to high pressure liquid chromatographic (HPLC) analysis on a 25 cm LiChrosorb Si60 (5 micron) column (2.2 mm id) by various means. First, the pesticide was analyzed directly with ultraviolet (UV) absorption detection at 254 nm and a mobile phase of trimethyl-pentane-isopropanol (96 + 4). After this, a fluorescent derivative was prepared, using dansyl chloride (5-dimethylaminonaphthalene-1-sulfonyl chloride), and analyzed by HPLC, using trimethylpentane-dioxane (95 + 5) as the mobile phase, with both UV absorption (254 nm) and fluorescence (excitation 365 nm, emission greater than 400 nm) detection. The response/ng for the dansyl derivative with fluorescence detection was 1.3 times greater than that for UV detection and 8 times more sensitive than direct UV detection of the carbamate. About 10 ppb carbaryl could be detected after derivatization in the foods studied; for direct analysis, 30-50 ppb could be detected at a 2:1 signal:noise ratio. Recoveries at 0.1 ppm averaged 90% by direct analysis compared with 78% after derivatization.

Carbaryl↗
PubMedDate not supplied

Amino acid sequence of rat submaxillary tonin reveals similarities to serine proteases.

Tonin, an esteroprotease isolated from rat submaxillary gland, is a serine protease with trypsin- and chymotrypsin-like activity. The substrate specificity of tonin shows that it differs from kallikreins and is definitely not a renin-like enzyme or an angiotensin-converting enzyme. Tonin can produce directly the vasoactive peptide angiotensin II, from angiotensin I, angiotensinogen and the synthetic tetradecapeptide substrate of renin by cleavage of a Phe-His bond. It has also been found to cleave some Phe and Arg bonds in various substrates such as beta-lipotropin (beta-LPH), adrenocorticotropin (ACTH), pro-opiomelanocortin (POMC) and substance P. Here we describe the complete amino acid sequence of rat submaxillary gland, tonin. Comparison of the sequence of 219 amino acids with other serine proteases, particularly kallikreins, gamma-subunit of nerve growth factor (NGF) and the recently described gamma-renin, reveals extensive similarities. More interestingly, it also reveals the substitution of an Asp residue always found in the serine protease active site triad (Asp, His, Ser) by a Leu residue. This unusual substitution does not seem to affect the proteolytic activity of the enzyme.

Amino Acid Sequence↗