Nonenzymatic Spontaneous Oxidative Transformation of 5,6-Dihydroxyindole.

Melanin is an important phenolic skin pigment found throughout the animal kingdom. Tyrosine and its hydroxylated product dopa provide the starting material for melanin biosynthesis in all animals. Through a set of well-established reactions, they are converted to 5,6-dihydroxyindole (DHI) and DHI-2-carboxylic acid (DHICA). Oxidative polymerization of these two indoles produces the brown to black eumelanin pigment. The steps associated with these transformations are complicated by the extreme instability of the starting materials and the transient and highly reactive nature of the intermediates. We have used mass spectral studies to explore the nonenzymatic mechanism of oxidative transformation of DHI in water. Our results indicate the facile production of not only dimeric and trimeric products but also higher oligomeric forms of DHI upon exposure to air in solution, even under nonenzymatic conditions. Such instantaneous polymerization of DHI avoids toxicity to self-matter and ensures the much-needed deposition of melanin at (a) the wound site and (b) the infection site in arthropods. The rapid deposition of DHI melanin is advantageous for arthropods given their open circulatory system; the process limits blood loss during wounding and prevents the spread of parasites by encapsulating them in melanin, limiting the damage.

Effect of monoclonal and polyclonal antibodies against conjugated neurotransmitter on experimental venous thrombosis.

Vasomotoricity in veins is largely controlled by the sympathetic nervous system. Norepinephrine and acetylcholine modulate the vasoconstrictor effect mediated by alpha-adrenergic receptors. Our objective was to study the role of local vasomotoricity in venous thrombosis, and particularly to determine some of the factors regulating it. Although no attempt has been described until now, polyclonal and monoclonal antibodies against L-dihydroxyphenylalanine, acetylcholine, and dopamine were administered in an experimental model of venous thrombosis. In view of the rather high specific antibody recognition for each compound, the presence of endogenous epitopes of L-dopa-like molecules and acetylcholine-like molecules in the circulation can be postulated. The results of this study may open an important new approach in the treatment of vascular diseases.