Intestinal absorption enhanced by unsaturated fatty acids: inhibitory effect of sulfhydryl modifiers
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Abstract— (1) The sulphydryl groups of brain white matter proteolipids were studied by alkylation with iodoacetic acid and iodoacetamide in an organic solvent medium. To make sterically hindered sulphydryl groups available, the reaction was also carried out in the presence of sodium dodecyl sulphate. (2) In all cases, iodoacetamide was a better alkylating agent than was iodoacetic acid. (3) Only minimal alkylation of crude white matter proteolipids was obtained in the absence of detergent; addition of sodium dodecyl sulphate increased the availablity of SH groups. (4) Purified proteolipids prepared by column chromatography were alkylated to a lesser degree than were crude proteolipids. (5) Prior reduction with mercaptoethanol resulted in the quantitative conversion of cysteine to S‐carboxymethylcysteine with either alkylating agent and in both preparations. (6) The possibility of a conformational difference between the protein in the crude and purified preparations is discussed.
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A collagenase in the culture supernatant of B. subtilis FS-2, isolated from traditional fish sauce, was purified. The enzyme had a molecular mass of about 125 kDa. It degraded gelatin with maximum activity at pH 9 and a temperature of 50°C. The purified enzyme was stable over a wide range of pH (5-10) and lost only 15% and 35% activity after incubation at 60°C and 65°C for 30 min, respectively. Slightly inhibited by EDTA, soybean tripsin inhibitor, iodoacetamide, and iodoacetic acid, the enzyme was severely inhibited by 2-β-mercaptoethanol and DFP. The protease from B. subtilis FS-2 culture digested acid casein into fragments with hydrophilic and hydrophobic amino acids as C-terminals, in particular Asn, Gly, Val, and Ile.
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If cysteine or cystine are identified in a protein, they require modification if they are to be quantified. Thiol groups may be blocked by a variety of reagents, including iodoacetic acid and iodoacetamide. Iodoacetate produces the S-carboxymethyl derivative of cysteine, effectively introducing new negative charges into the protein. Where such a charge difference is undesirable, iodoacetamide may be used to produce S-carboxyamidomethylcysteine (on acid hydrolysis, as for amino acid analysis, this yields S-carboxymethylcysteine). The charge difference between these two derivatives has been utilized in a method to quantify the number of cysteine residues in a protein ([1], see Chapter 83).
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The apparent activity of the second component of human complement was enhanced by treatment of the purified protein with iodoacetamide. By contrast, treatment with iodoacetic acid or p-chloromercuribenzoate led to inactivation. Treatment with iodoacetamide prevented the effect of p-chloromercuribenzoate and vice versa. Enhanced activity was partly due to increased stability of the otherwise labile intermediate complex consisting of erythrocytes, antibody, and the first, second, and fourth components of complement.
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If cysteine or cystine is identified in a protein it requires modification in order to be quantified. Thiol groups may be blocked by a variety of reagents including iodoacetic acid and iodoacetamide. Iodoacetate produces the S-carboxymethyl derivative of cysteine, effectively introducing new negative charges into the protein. Where such a charge difference is undesirable, iodoacetamide may be used to derivatize cysteine to S-carboxyamidomethylcysteine (on acid hydrolysis, as for amino acid analysis, this yields S-carboxymethylcysteine). The charge difference between these two derivatives has been utilized in a method to quantify the number of cysteine residues in a protein ([1], see Chapter 89 ).
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The sulfhydryl reagents iodoacetic acid, iodoacetamide, p -chloromercuribenzoate and N-ethylmaleimide were capable of inhibiting norepinephrine-stimulated lipolysis in isolated adipose cells. In addition, iodoacetamide inhibited lipolysis stimulated by theophylline and by dibutyryl cyclic adenosine monophosphate. The data indicate a probable intracellular site of action, possibly upon a triglyceride lipase. The dithiol dimercaprol was capable of preventing the inhibitory action of the compounds but could not reverse established inhibition. The monothiol mercaptoethanol could prevent the inhibition of N-ethylmaleimide. Elucidation of the ultimate mechanism of inhibition by these compounds awaits isolation of the entire system for lipase activation from adipose tissue.
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