The structure of albumin 2 protein fraction of amaranth was investigated. It was formed by several major polypeptide subunits of molecular masses of 52.3 ± 0.8, 54 ± 2, and 56 ± 1 kDa. The former and the latter subunits were composed of a peptide of molecular mass between 31 and 38 kDa linked by S−S bonds with another peptide of molecular mass between 19 and 23 kDa. The 54 kDa subunit together with the 31−38 and 19−23 kDa subunits formed S−S-linked aggregated polypeptides. Lyophilized albumin 2 was highly polymerized, having a complex monomer component with a molecular mass of 300 ± 10 kDa. The polymers were partially stabilized by SS linkages. Because of these structural characteristics, albumin 2 was very similar to amarantin except for the presence of the 54 kDa subunit and its tendency to polymerize. Two components were obtained by gel filtration of globulin fraction. The major one exhibited heterogeneity of species and showed some common features with albumin 2. The minor component eluted at a lower volume and also showed heterogeneity, with a main species of 7S and a minor one of 12S. Their major peptides had molecular masses of 78, 72, 39, 30, and 20 kDa similar to the 7S type globulin. Its size, larger than that of amarantin, is different from a 7S type globulin, but the possibility of becoming polymerized or having a shape quite different from that of a sphere cannot be dismissed. Keywords: Amaranth; globulin; albumin 2; protein structure; gel filtration; electrophoresis

A comparative analysis of the microbiological quality of three turbot (Scophthalnus maximus) farms (A, B, and C) located in Galicia (northwest Spain) is given. The microbial load and types of bacteria in the internal organs (liver and kidney) of apparently healthy fish was monitored over a year, and all the disease problems occurring during this survey were analyzed. The percentage of healthy turbot in which positive bacterial growth was obtained was relatively high in the three ongrowing facilities. Farm A exhibited the poorest conditions of fish health with an average of 42% fish infected, while farm B showed the best microbiological quality with 27% of turbot harbouring bacteria in the internal organs. In all three farms, a wide range of bacteria was found in healthy turbot with Vibrio (V. splendidus-V pelagius, Vfisheri-V harveyi and Vibrio spp.) and Pseudomonas spp. being the predominant groups comprising at least 80% of the total bacterial isolates in each farm. The highest number of pathological problems (22) with the most diverse bacterial flora occurred in farm A. Vibrio spp. and Pseudomonas spp. were the most prevalent bacteria recovered from diseased turbot. Haemorrhages in palate and jaws, tail and fins, and ulcerative lesions were the most frequent external clinical signs of diseased fish recorded in the three farms. However, it was not possible to associate a particular bacterial species with a specific pathology. Routine use in farm A of oxolinic acid and nitrofurantoin may have led to the development in the Vibrio strains of resistances to both chemotherapeutants (up to 25%).

The influence of pH and NaCl on the structure of globulin-P, the polymerizable amaranth 11S type globulin, was studied by differential scanning calorimetry, gel filtration, and gradient sedimentation. At μ = 0.54, the protein is stable for pH ranging from 5 to 9 but becomes rapidly unfolded as pH decreases below 5. For pH values above 9, globulin-P denatures more gradually than in acidic medium, and it also dissociates into subunits, which are possibly less thermostable. At pH 6.5 or 8.5 and low sodium chloride concentrations (μ ≤ 0.01), dialyzed globulin-P destabilizes, yielding species of lower thermal stability. The increase in NaCl concentration up to 0.1 M induces folding of globulin-P toward a more stable structure. Above 0.1 M NaCl, increasing the ionic strength up to μ = 0.5 elevates the denaturation temperature (T d) and denaturation enthalpy (ΔH). From μ = 0.1 to 0.5 the content of soluble globulin-P polymers decreases, possibly owing to protein insolubilization. Above 0.5 M, NaCl shows a stabilizing effect reflected by increasing T d, whereas ΔH stays constant; this effect is similar to that found by other authors in some storage proteins. Keywords: Amaranth; globulin; protein structure; gel filtration; ultracentrifugation; pH effect; ionic strength effect