Gwynne H. Little

A simple rapid biuret method for the estimation of protein in samples containing thiols

Abstract Interference in the Lowry protein determination by thiol compounds is now well known (1–3). We have found that the estimation of protein by the biuret reaction is also subject to interference when the protein sample contains various thiols. We wish to report that this interference can be prevented in most cases by using a biuret reagent which is chelated with ethylenediaminetetraacetate (EDTA). In samples containing dithiothreitol (DTT) it is also necessary to add iodoacetamide prior to the addition of the biuret reagent. The use of iodoacetate to eliminate thiol interference in the Lowry procedure has been reported previously (3). This report details the extent of interference of dithiothreitol, β-mercaptoethanol, β-mercaptoethylamine, and glutathione, and illustrates the extent of neutralization which is attained in each case. We have also introduced modifications which permit the development of a stable color in only 5 min.

Inhibition of programmed cell death by catalase and phenylalanine methyl ester.

1. Programmed cell death proceeds by an unknown mechanism which results in characteristic morphological changes known as apoptosis. 2. We have proposed that, in hormone-induced apoptosis, cell death may be the result of an attack of cells destined to die by cytotoxic macrophages. 3. We have investigated the effects of superoxide dismutase, catalase and the macrophage toxin, phenylalanine methyl ester, on the regression of tadpole tail slices in culture. 4. Our findings, that regression of bullfrog tadpole tails is blocked by catalase and phenylalanine methyl ester, support the working hypothesis.

Changes in the rate of production of superoxide anion in tails of Rana catesbeiana tadpoles during spontaneous and triiodothyronine-induced metamorphosis

1. The time course of changes in the rate of production of superoxide anion (O2) was compared with that of beta-glucuronidase in tails of Rana catesbeiana tadpoles during spontaneous and triiodothyronine (T3)-induced metamorphosis. 2. Superoxide production increases in tadpole tail tissue undergoing regression in vivo during spontaneous metamorphosis and in response to T3 treatment. 3. The specific activity of beta-glucuronidase rises three-fold relative to control levels in tadpoles treated with T3 in vivo. 4. The time of onset of the rise in beta-glucuronidase activity precedes the onset of tissue regression and the onset of the increase in superoxide production precedes the rise in beta-glucuronidase activity.

Serum cholinesterase inhibition by boronic acid

Horse serum cholinesterase (acylcholine acylhydrolase, EC 3.1.1.8) was reversibly inhibited by a variety of alkyl- and areneboronic acids with Ki values ranging from 6.2 mM (methaneboronic acid) to 3.1 microM (diphenylboric acid). Binding to the enzyme was apparently at the active center, because inhibition obeyed competitive kinetics and because boronic acids protected the enzyme from inactivation by phenylmethanesulfonyl fluoride. Boronic acids should prove useful in probing the active center of serum cholinesterase.

Bile pigments and bilirubin UDP-glucuronyl transferase during the metamorphosis of Rana catesbeiana tadpoles☆

The major bile pigments in Rana catesbeiana tadpoles was bilirubin IX alpha. The concentration of bilirubin IX alpha increases in bile and plasma during metamorphosis. Bilirubin IX alpha and biliverdin IX alpha were also present in the bile of tadpoles. Bilirubin UDP-glucuronyl transferase activity was present in the livers of all tadpoles examined. Bilirubin UDP-glucuronyl transferase activity increases slightly during spontaneous metamorphosis and increases approximately 2-fold during T3-induced metamorphosis.

Alanine aminopeptidase activity and autolysis in the tails of Rana catesbeiana larvae during metamorphosis

1. Alanine aminopeptidase activity and autolysis increase concomitantly in tail tissue of Rana catesbeiana tadpoles during metamorphosis. 2. significant increases first appear at Taylor and Kollros state XX and coincide with the beginning of tail regression as determined by the tail wt body wt ration. 3. The results suggest a role of alanine aminopeptidase in the mechanism of tail resorption.

Programmed cell death in the anuran tadpole tail requires expression of a cell surface glycoprotein

Programmed cell death is generally perceived as a suicide process involving activation of an internal death program thought to be common to all cells. We have previously presented evidence supporting the view that, at least in the tadpole tail, programmed cell death may involve assassination by cytotoxic cells such as resident macrophages. In this report, we show that regression of tadpole tail slices in culture is blocked by tunicamycin and brefeldin A, demonstrating that the intracellular protein trafficking machinery must be intact. Regression is also blocked by concanavalin A and fucose, suggesting a requirement for a cell surface glycoprotein. These observations are consistent with our hypothesis that programmed cell death requires expression of specific markers on the surfaces of cells destined to die, identifying the cells bearing those markers as targets for destruction.

Taurine levels in the anuran tadpole tail during spontaneous and triiodothyronine-induced metamorphosis

Abstract o 1. Taurine levels were determined in tail tissue of Rana catesbeiana tadpoles during spontaneous and triiodothyronine-induced metamorphosis. 2. Taurine levels increased prior to the beginning of tail regression in spontaneous metamorphosis and then declined to premetamorphic levels. 3. No changes in taurine levels occurred in triiodothyronine-treated animals. 4. Implications of these findings are discussed.