Catecholamines definition

While the catecholamines definitely play a part in the pathophysiology of the hypertension caused by the phaeochromocytoma, the question as to whether amines indigenous to be body are of importance in the forms of hypertension known as essential , has not yet been solved. As noradrenaline is the main transmitter of sympathetic nerve impulses which cause vasoconstriction, the question as to the pathogenetic role of noradrenaline in essential hypertension coincides with that of general importance of neural... 

More definite evidence for the transient existence of the un-cyclized l-(jS-aminoethyl)-3,4-benzoquinones has been obtained recently by Kodja and Bouchilloux,77 78 who noted that a transient yellow color (Amax ca. 385 mp) was occasionally observed during the enzymic oxidations of catecholamines (particularly in unbuffered systems at low temperatures). This phenomenon was probably due to the formation of the transient o-quinones. (The absorption maximum of o-benzoquinone, the effective chromophore of the open-chain quinones, is known to occur at ca. 390 mp.79) An absorption maximum at 390 mp is characteristic of the formation of the dopa-quinone chromophore during oxidation of small C -terminal tyrosine peptides in the presence of tyrosinase.37 48 Similar spectroscopic features were observed when the oxidations were carried out with lead dioxide in sulfuric acid solutions (pH> 1). If the initial oxidation was carried out for a short period of time, it was possible to regenerate the original catecholamines by reduction (e.g. with sodium bisulfite, potassium iodide, and zinc powder) and to show that the 385 mp peak disappeared.77,78 Kodja and Bouchilloux were also able to identify 2,4-dinitrophenylhydrazones of several of the intermediate non-cyclized quinones by paper chromatography and spectroscopy (Amax n weakly acid solution ca. 350 mp with a shoulder at ca. 410 mp).77,78... 

Tyrosine is a (crystalline) amino add with the formula HOQH4CH2CH(NH2) COOH. It results from the hydrolysis of proteins, that is, the reaction of proteins with water. The -C6H4- group within the compoimd denotes a ring-type stmcture. Another definition provided is that tyrosine is found in most proteins and can be synthesized metabolically from phenylalanine. Furthermore, tyrosine is a precursor for thyroid hormones, melanin (the dark pigment of body parts, notably, the skin), and catecholamines (that affect the sympathetic nervous system). 

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