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Biomedical subjects

C A Benassi

Publications and source records attributed to C A Benassi.

At least 19 recordsLinked to original sources
PubMed1991

Silicon membrane interface for the direct analysis of Kathon CG in aqueous solutions and cosmetic emulsions.

An easy determination of Kathon CG, an antimicrobial agent widely used in cosmetic and toiletry products, has been achieved by means of silicone membrane interfaced mass spectrometry. Low levels of the above preservative (up to p.p.b.) could be easily detected in both aqueous solutions and cosmetic emulsions. Valuable information has been obtained on the stabilization and decomposition processes to which the organic components of Kathon CG are subject. The role of magnesium ions, which are present as a stabilizing agent in Kathon CG formulation, in these processes has been investigated, leading to the identification of some degradation products.

Cosmetics↗
PubMed1989

High-performance liquid chromatographic determination of free formaldehyde in cosmetics.

An improved, sensitive method for the determination of formaldehyde in cosmetics and other commercial products is reported. The procedure is based on dilution of the sample with tetrahydrofuran-water (9:1), followed by precolumn derivatization with 2,4-dinitrophenylhydrazine and direct reversed-phase high-performance liquid chromatography. The formaldehyde derivative is stabilized in the reaction medium by addition of phosphate buffer and neutralization and detected in less than 10 min by the standard additions methods. The method also appears to be suitable for the direct evaluation of the formaldehyde donors used in cosmetics as preservatives.

Chromatography, High Pressure Liquid↗
PubMed1987

Purification, modification, physico-chemical and pharmacokinetic characterization of arginase, an enzyme of potential use in therapy.

Beef liver arginase, an enzyme potentially useful in the therapy of arginine dependent tumors or of familial hyperargininemia, was purified to homogeneity by a procedure involving a key step of hydrophobic affinity chromatography. The enzyme was extensively modified by the covalent linking of monomethoxypolyethyleneglycol molecules according to a procedure recently proposed by the Authors (Veronese et al., Appl. Biochem. Biotecnol. 11, 869, 1985) without any significant loss of activity. The derivative enzyme presents more convenient properties for a therapeutic use, as compared to the native enzyme, such an increased structural stability, a decreased digestion by proteolytic enzymes and an expanded clearance time in rats.

Animals↗
PubMed1985

Surface modification of proteins. Activation of monomethoxy-polyethylene glycols by phenylchloroformates and modification of ribonuclease and superoxide dismutase.

A single-step method of activation of monomethoxypolyethylene glycols suitable for its binding to polypeptides and proteins is proposed. Based on the reaction with 2,4,5-trichlorophenylchloroformate or p-nitrophenylchloroformate, it gives reactive PEG-phenylcarbonate derivatives. The PEG intermediate is stable on storage, the activating group is easily quantified,and the reaction with amino acid and proteins proceeds rapidly at pH near neutrality. The PEG derivatization of enzymes with this procedure is less inactivating than those previously reported. Ribonuclease and superoxide dismutase were modified and the effect of (a) bound polymer on clearance time in rats, (b) antibody recognition, and (c) on the enzymatic activity toward low and high molecular weight substrates were studied.

Amino Acids↗
PubMed1985

A rapid HPLC technique for determining levels of histamine in tears from normal and inflamed human eyes.

Because of the important role of histamine in the inflammatory process, the measurement of histamine levels in tears has been considered as a possible index of eye irritancy. Histamine levels have been measured using an HPLC procedure involving fluorimetric detection after fluorescamine derivatization. Analyses, at picomole levels, were carried out in less than 5 minutes using 10 microliter of tear samples collected from either normal or inflamed human eyes.

Chromatography, High Pressure Liquid↗
PubMed1984

Enzymatically active subunits of Bacillus stearothermophilus enolase bound to Sepharose.

The octameric enolase from Bacillus stearothermophilus was immobilized onto Sepharose 4B activated by the cyanogen bromide reaction under conditions for achieving essentially a single-point attachment. The immobilized enzyme was dissociated with guanidine hydrochloride to yield bound monomeric enolase. The Sepharose-bound subunit regained activity upon removal of the denaturant. It was also possible to rehydribize immobilized monomers to native octamers. Of note, the thermal stability of the immobilized enolase subunit does not appreciably differ from that of the parent soluble octameric enzyme. Thus, these results indicate that single subunits of thermophilic enolase are active and that oligomerization is not a prerequisite for the enzymic activity as well as for thermal stability.

Enzymes, Immobilized↗
PubMed1977

Arginine modification in Kunitz bovine trypsin inhibitor through 1, 2-cyclohexanedione.

Arginine residues (5.5 out of 6) of the trypsin-kallikrein inhibitor from bovine organs (Kunitz inhibitor) were selectively modified by reaction with 1, 2-cyclohexanedione in sodium borate buffer, pH 9.0. The modified inhibitor is still highly active in inhibiting trypsin and chymotrypsin at 1:1 inhibitor: enzyme molar ratio and full inhibition was achieved at slightly higher molar ratio. The extent of correct refolding, upon reoxidation, of the reduced, arginine-modified inhibitor is diminished and regeneration of two arginines occurred under the reduction conditions. The stability constants and the standard-free energies of binding of the complexes between trypsin, or chymotrypsin, and the native, the arginine-modified and the reduced and reoxidized arginine-modified inhibitor have been determined from inhibitory assays.

Amino Acids↗
PubMed1977

Drug-protein interaction: the binding of cephalosporins to albumins.

The binding of some cephalosporin antibiotics, namely cephalothin, cephaloridine and cephalexin, to serum albumins was quantitized using a fluorescence probe technique. The results suggest that these drugs bind to hydrophobic sites on serum albumins. The association constants of the three drugs with bovine serum albumin showed the strongest binding for cephalothin (Ka 1.2 x 10(3) M(1)) and weaker ones for cephaloridine and cephalexin (Ka 0.59 and 0.4 x 10(3) M(-1)). Serum albumin from different species was also investigated, only minor variations in the binding properties being found.

Animals↗
PubMed1976

On the reaction of acetamidomethanol with native and reduced bovine pancreatic trypsin inhibtor (Kunitz inhibitor).

The stability of native and reduced bovine pancreatic trypsin inhibitor (Kunitz inhibitor) in anhydrous hydrogen fluoride and their reaction with acetamidomethanol, in the same solvent, have been investigated. The bovine Kunitz inhibitor appears to be stable in liquid hydrogen fluoride but the reduced molecule loses about 50% of its ability to regain inhibitory power, upon air oxidation, by exposure to this solvent. Tyrosine residues appear to be affected by acetamidomethylation of the native protein to give a modified inhibitor which is still highly active in inhibiting trypsin. The extent of correct refolding, upon reoxidation, of the reduced tyrosine modified-inhibitor is greatly diminished. Tyrosine modification can be prevented by carrying out the acetamidomethylation reaction in the presence of excess anisole. The stability constants and the standard free energies of binding of the complexes between trypsin and the native and the tyrosine modified-inhibitor have been determined.

Acetamides↗
PubMed1976

Studies on trypsin inhibitors. Part I. Synthesis of protected peptides related to sequence 1-10 of porcine pancreatic secretory trypsin inhibitor II (Kazal).

The general strategy for the synthesis, by conventional procedures, of the entire sequence of porcine pancreatic secretory trypsin inhibitor II (Kazal) is discussed. The synthesis of two protected peptides corresponding to positions 2-10 and 1-10 of the proposed primary structure of the inhibitor is described. The heptapeptide free base threonyl-S-acetamidomethylcysteinylthreonylseryl-gamma-tert-butylglutamylvalylserine tert-butyloxycarbonylhydrazide (sequence 4-10) was acylated, by the azide procedure, with either the dipeptide benzyloxycarbonyl-gamma-tert-butylglutamylalanine hydrazide (sequence 2-3) or the tripeptide Nalpha-benzyloxycarbonyl-Nomega-nitroarginylglutamylala-nine hydrazide (sequence 1-3). The stereochemical homogeneity of the resulting peptides, benzyloxycarbonyl-gamma-tert-butylglutamylalanylthreonyl-S-acetamidomethyl-cysteinylthreonylseryl-gamma-tert-butylglutamylvalylserine tert-butyloxycarbonylhydrazide and Nalpha-benzyloxycarbonyl-Nomega-nitroarginylglutamylalanylthreonyl-S-acetamido-methylcysteinylthreonylseryl-gamma-tert-butylglutamylvalylserine tert-butyloxycarbonyl-hydrazide, was assessed, after partial deprotection with liquid hydrogen fluoride, by digestion with aminopeptidase M followed by quantitative amino acid analysis.

Alanine↗