An enone reductase from Nicotiana tabacum: cDNA cloning, expression in Escherichia coli, and reduction of enones with the recombinant proteins

In the course of the purification of enone reductase participating to the reduction of pulegone, two reductases (NtRed-1 and NtRed-2) were isolated from cultured cells of Nicotiana tabacum. The partial amino acid sequences of the reductases revealed that NtRed-1 was allyl-alcohol dehydrogenase (Accession No. BAA89423) and NtRed-2 was malate dehydrogenase (Accession No. CAC12826). cDNA cloning and expression of these reductases in Escherichia coli were performed. Reduction with recombinant proteins was examined with cyclic α,β-unsaturated ketones, such as pulegone, carvone and verbenone, as substrates. It was found that the recombinant NtRed-1 catalyses the hydrogenation of the exocyclic C-C double bond of pulegone.     

Toxic activity from cultures of Karlodinium micrum (=Gyrodinium galatheanum) (Dinophyceae)—a dinoflagellate associated with fish mortalities in an estuarine aquaculture facility

The goal of this study was to test for, and partially characterize, toxic activity associated with the dinoflagellate Karlodinium micrum. Since 1996, three fish kill events associated with blooms of K. micrum have occurred at HyRock Fish Farm, an estuarine pond aquaculture facility raising hybrid striped bass on the Chesapeake Bay, MD, USA. Using an assay based on the lysis of rainbow trout erythrocytes, cultures of a Chesapeake Bay isolate of K. micrum have been shown to produce toxic substances which are released upon cell disturbance or damage. The LC₅₀ for hemolysis of a sonicated cell suspension was 2.4×10⁴ cells ml⁻¹, well within the range of cell concentrations observed associated with fish kills. The toxic activity from K. micrum cells and culture filtrates was traced to two distinct fractions that co-elute with polar lipids. The LC₅₀ for hemolysis of the larger of these two fractions (Tox A) was 284 ng ml⁻¹ while the LC₅₀ of the second, smaller, fraction (Tox B) was 600 ng ml⁻¹. For comparison, the LC₅₀ for the standard hemolysin saponin was 3203 ng ml⁻¹. At concentrations of 800 and 2000 ng ml⁻¹, respectively, Tox A was further shown to be ichthyotoxic to zebrafish (Danio rerio) larvae (80% mortality), and cytotoxic to a mammalian GH(4)C(1) cell line (100% LDH release). At a concentration of 600 ng ml⁻¹ Tox B was shown to be cytotoxic to a mammalian GH(4)C(1) cell line (>30% LDH release), but not ichthyotoxic to zebrafish (D. rerio) larvae up to a concentration of 250 ng ml⁻¹. Although treatment with either algicidal copper or potassium permanganate caused significant lysis of K. micrum cells (>70%), toxic activity was released after treatment with copper and eliminated following treatment with potassium permanganate. This observation in cultures is consistent with observations made at HyRock Fish Farm where significantly higher mortality was observed following treatment of a K. micrum bloom with copper sulfate compared to treatment with potassium permanganate. This study represents the first direct evidence of the toxicity of K. micrum isolated from the Chesapeake Bay.     

Effects of cold (+4°C) on thyroid metabolism of iodine (I and I) in quail (Coturnix coturnix japonica)—A comparison with the rat

1. 1.|A kinetic study of the absolute specific activity (SA) of iodine in intrathyroidal iodotyrosines and iodothyronines, and in plasma PBI, was performed comparatively in adult male rats and quail kept at +25°C (controls) or exposed to +4°C (for 2 days or 30 days before the iodine measurements).

2. 2.|In both species, 2 days of cold exposure induced a rapid increase (20 to 50%) in the SA of intrathyroidal iodoaminoacids and plasma PBI, leading to a rapid equilibration between the SA measured. After 30 days an acceleration in iodine turnover was still measurable in rats, but the stimulation then appeared more important in quail. In addition, the acceleration of iodine turnover led to a characteristic bimodal pattern of this turnover which was apparent only in quail, and could reflect an important production of non-hormonal iodinated proteins. Although the bird thyroid has been claimed to be less reactive to cold than its mammalian homologues, the present study indicates that, at least in bird species whose thyroidal stores of iodine are not excessive, the thyroid is even more responsive to cold than the rat thyroid.