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The technique of photo affinity labeling of tyrocidine synthetase 1(TY1) with 2-azidoadenosine triphosphate (2-azido-ATP), applied in the study of a nucleotide binding domain in peptide synthetases, revealed a loss of catalytic activity and a time dependent covalent modification of the enzyme when TY1 was exposed to ultra-violet radiation in the presence of photolabel. The components of the nucleotide binding domain were observed near the adenine ring in ATP.

The first detailed phycotoxin analysis of shellfish Mytilus galloprovincialis (Lamarck, 1819) from the Eastern-mid Adriatic Sea (Croatia) has been conducted. Mussel samples were collected from a localized site in the Vranjic Basin (Kaštela Bay, Croatia) over the years 2004 and 2005. Analysis of shellfish toxicity was performed using the mouse bioassay, separation by HPLC, and the ELISA assay. Obtained results demonstrate the predominant presence of yessotoxin (YTX), and an occasional occurrence of toxins from the diarrheic shellfish poisoning (DSP) group of compounds. Phytoplankton analysis of corresponding sea water samples, collected in the investigated area, showed the presence of Lingulodinium polyedrum and Gonyaulax spinifera, potential sources of YTX, as well as the occurrence of dinoflagellates of the genera Dinophysis and Prorocentrum, associated with DSP toxicity. [ABSTRACT FROM AUTHOR]

Although alkaline phosphatase (APase) from Escherichia coli crystallizes as a symmetric dimer, it displays deviations from Michaelis-Menten kinetics, supported by a model describing a dimeric enzyme with unequal subunits [Orhanović S., Pavela-Vrancic M. and Flogel-Mrsić M. (1994) Acta. Pharm.44, 87-95]. The possibility, that the observed asymmetry could be attributed to negative cooperativity in Mg2+ binding, has been examined. The influence of the metal ion content on the catalytic properties of APase from E. coli has been examined by kinetic analyses. An activation study has indicated that Mg2+ enhances APase activity by a mechanism that involves interactions between subunits. The observed deviations from Michaelis-Menten kinetics are independent of saturation with Zn2+ or Mg2+ ions, suggesting that asymmetry is an intrinsic property of the dimeric enzyme. In accordance with the experimental data, a model describing the mechanism of substrate hydrolysis by APase has been proposed. The release of the product is enhanced by a conformational change generating a subunit with lower affinity for both the substrate and the product. In the course of the catalytic cycle the conformation of the subunits alternates between two states in order to enable substrate binding and product release. APase displays higher activity in the presence of Mg2+, as binding of Mg2+ increases the rate of conformational change. A conformationally controlled and Mg2+-assisted dissociation of the reaction product (Pi) could serve as a kinetic switch preventing loss of Pi into the environment.