Cyanobacterial Harmful Algal Blooms: Chapter 15: Cyanotoxins Workgroup Report

The Cyanotoxins Workgroup was charged with the identification and prioritization of research needs associated with: the identification of cyanotoxins; toxicokinetics and toxicodynamics of cyanotoxins; human susceptibility to the toxins; cyanobacterial genetics/omics and factors for inclusion in predictive models of toxin production; and risk reduction from an intentional or accidental release of cyanotoxins. Papers presented for the Cyanotoxins Session of the symposium on toxin types, toxicokinetics, and toxicodyamics (See Humpage this volume), cyanobacterial genetics of toxin production (See Neilan this volume), and parameters related to human risks from cyanobacterial exposure (See Love this volume) set the stage for Cyanotoxins Workgroup discussions. A consensus was achieved regarding the need to focus on the major identified classes of cyanotoxins. The group expressed the belief that the most significant toxic components of presently occurring harmful algal blooms have been identified, and the knowledge gaps for these most prevalent toxins are great enough to warrant the attention of most of our future research. This belief does not negate the need to study mixtures of cyanotoxins and toxin precursors, especially those most likely to occur within a given bloom. Moreover, there is also a significant likelihood that novel cyanobacterial blooms and toxins will continue to emerge, and future identification of unknown bloom-forming species and their toxins will require ongoing diligence

Carboxylesterases (EC 3.1.1). Kinetic Studies on Carboxylesterases

Kinetic evidence has been obtained which is consistent with the formation of an acyl-enzyme intermediate in the hydrolysis of butyrate esters catalyzed by pig liver carboxylesterase. A study of the pig liver carboxylesterase- catalyzed hydrolysis of phenyl butyrate revealed activation by substrate and by modifiers such as benzene. This activation has been interpreted in terms of a classical kinetic scheme involving sites for substrate and modifier on a single enzyme molecule. For a series of activated esters, the catalytic rate constants for the carboxylesterase-catalyzed hydrolyses were found to be relatively insensitive to changes in the acyl group, indicating that binding is not responsible for the high reactivity of these systems. Kinetic and other data suggest that there are possibly some different elements of essential chemistry between the esterases and the proteinases