Protein determination in materials containing melanin

1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide interference with Lowry method

1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) was tested for interference with the Lowry method of protein determination. The EDC interference was nearly additive at both 660 and 750 nm. Blue-colored complex developed in the case of EDC and showed maximum absorbance at 750 nm, similar to the bovine serum albumin (BSA) estimation. In time response analysis, blue-colored complex was developed after 30 min of incubation in both cases (EDC and BSA); therefore, it followed the same kinetic pattern of color development as that of BSA. Interference is believed to be caused by the reduction of the folin-ciocalteu reagent by EDC, resulting in increased blue-colored complex and apparently causing increased protein content of the sample.

Isolation and biophysical studies of natural eumelanins: applications of imaging technologies and ultrafast spectroscopy

The major pigments found in the skin, hair, and eyes of humans and other animals are melanins. Despite significant research efforts, the current understanding of the molecular structure of melanins, the assembly of the pigment within its organelle, and the structural consequences of the association of melanins with protein and metal cations is limited. Likewise, a detailed understanding of the photochemical and photophysical properties of melanins has remained elusive. Many types of melanins have been studied to date, including natural and synthetic model pigments. Such studies are often contradictory and to some extent the diversity of systems studied may have detracted from the development of a basic understanding of the structure and function of the natural pigment. Advances in the understanding of the structure and function of melanins require careful characterization of the pigments examined so as to assure the data obtained may be relevant to the properties of the pigment in vivo. To address this issue, herein the influence of isolation procedures on the resulting structure of the pigment is examined. Sections describing the applications of new technologies to the study of melanins follow this. Advanced imaging technologies such as scanning probe microscopies are providing new insights into the morphology of the pigment assembly. Recent photochemical studies on photoreduction of cytochrome c by different mass fraction of sonicated natural melanins reveal that the photogeneration of reactive oxygen species (ROS) depends upon aggregation of melanin. Specifically, aggregation mitigates ROS photoproduction by UV-excitation, suggesting the integrity of melanosomes in tissue may play an important role in the balance between the photoprotective and photodamaging behaviors attributed to melanins. Ultrafast laser spectroscopy studies of melanins are providing insights into the time scales and mechanisms by which melanin dissipates absorbed light energy.

Quantification of lipids, liposomes, amino acids, and proteins by thermal ultramicrodigestion and an ultramicrocoulometric assay, based on the reaction of hypobromite with ammonia

The quantification of nitrogen in organic material is described. It is based on a novel thermal ultramicrodigestion in combination with an ultramicrocoulometric quantification. The lower detection limit of the coulometric measurement is 0.5 microg nitrogen, which corresponds to 20 microg lipid, 3 microg glycine, or 4 microg protein. Therefore it is as sensitive as the frequently used Lowry method. In contrast to the Lowry protein determination it is not disturbed by detergents and most other interfering substances.

Melanins production from enkephalins by tyrosinase

Leu-enkephalin and Met-enkephalin are oxidized in vitro by mushroom and sepia tyrosinase giving rise to synthetic melanins whose production is dependent on incubation time and on enzyme concentration. The Enk-melanins formed are acid-insoluble brownish or reddish pigments showing a continuous absorbance in the visible region when dissolved in basic solution. The presence of the amino acid chain makes them fully soluble in pH 7.4 0.05 M phosphate buffer and methanol.