N-Acetyltransferase, which is suggested to be responsible for the production of N1-acetylspermidine in Leishmania amazonensis and to be involved in the process of inactivation and degradation of excessive polyamines, was partially purified and characterized. Among the substrates tested, sym-norspermidine, sym-norspermine, and 1,3-diaminopropane had the highest reaction rates, but the naturally occurring polyamines spermine and spermidine were also acetylated at considerable rates, whereas putrescine was a poor substrate. The Michaelis constants (Km values) for spermine and spermidine were 0.66 and 3.3 mM, respectively. The Km value for acetylcoenzyme A (acetyl-CoA) was determined to be 34 microM. CoA inhibited the reaction in a competitive manner; the inhibition constant was 5 microM. The enzyme showed an apparent relative molecular mass of 35,000.
The characteristics and kinetic properties of an arylalkylamine N-acetyltransferase were studied in partially purified preparations of the human filarial parasite Onchocerca volvulus. The enzyme, which had a relative molecular mass (M(r)) of 37-38 kDa, catalyzed the acetylation of arylalkylamines but did not accept arylamines or polyamines as substrates. The optimal pH for enzyme activity was found to be 8.5 in TRIS-HCI. The apparent Michaelis constant (K(m)) and maximum velocity (Vmax) determined from Lineweaver-Burk plots for tryptamine were 1.8 microM and 29 nmol min-1 mg protein-1, respectively. Except for the catecholamines, the other arylalkylamines such as 5-hydroxytryptamine (5-HT), tyramine, and octopamine similarly exhibited high affinities and reaction rates. Whereas the enzyme is inhibited by metals and p-chloro-mercuribenzoate, it is inactivated neither by amethopterin nor by cystamine and is thereby distinguished from the mammalian arylamine N-acetyltransferase. Like other N-acetyltransferases whose function is the regulation of intracellular amine levels, the enzyme may have a role in the inactivation of excess biogenic amine in this parasite.
A cytosolic polyamine N-acetyltransferase that preferentially catalyzes the acetylation of spermidine in the N8-position was identified in the free-living pathogenic amoeba Acanthamoeba culbertsoni. In addition to spermidine, the enzyme also catalyzed the acetylation of spermine and putrescine with Michaelis constants (Km values) of 97, 12, and 10 microM, respectively. The Km value for acetylcoenzyme A (acetyl-CoA) was estimated to be 11 microM, whereas CoA had an inhibitory constant of 6 microM. The N-acetylase has a molecular mass of approximately 45 kDa. That the enzyme preferentially catalyzed the acetylation of spermidine at the N8-position, resulting in N8-acetylspermidine, the preferred substrate of the polyamine oxidase found in A. culbertsoni, indicates a role for the enzyme in the production of 1,3-diaminopropane, the major polyamine found in the Acanthamoeba.
of a single altered behaviour, are pleiotropic and therefore defective in other chemical sensitivities. 4. The Dyf phenotype is associated with the loss of sensiti vity to many different chemicals. Alterations in the shape or matrix content of the amphidial channel also result in a Dyf phenotype. 5. While water soluble chemicals seem to have receptors on the neurons whose cilia are exposed to the outside (ASH and ADD, attraction to and repulsion by volatile chemicals are mediated by receptors present on the amphidial wing cells AWA, AWES and AWC.
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