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Characterization of cod myosin aggregates using static and dynamic light scattering

Author(s):

Tom Brenner, Ragnar Jóhannsson, Taco Nicolai

Funded by:

Matís, Rannís, AVS

Characterization of cod myosin aggregates using static and dynamic light scattering

Myosin var einangrað úr þorski með mismunandi aðferðum sem skiluðu klösum af hreinu myosini. Þessir klasar innihéldu milli 8 og 20 myosin sameindir, og voru stöðugir við kaldar aðstæður (T<20°C) og í þynntum lausnum (C<5g/L) með 0.5M KCl við pH 6.0 til 8.0. Við hærri styrk próteins geljaðist það eða féll út. Klösunin við lágan styrk var skoðuð með gleypnimælingum og ljósdreifingu. Klösunin hætti eftir langan hitunartíma í flestum tilfellum, en við ákveðnar kringumstæður hélt hún þó áfram og leiddi til útfellingar próteinsins. Kæling leiddi til frekari klösunar, sem virðist vera afturkræf m.t.t. endurhitunar. Bygging klasanna var ákvörðuð eftir kælingu og útþynningu. Sjálflíkir klasar voru greindir, með brotvídd 2.2. Stærð klasanna jókst með hækkandi hitastigi (30-70°C), hækkandi próteinstyrk (0.4-3 g/L) og lækkandi pH (8.0-6.0). Bygging klasanna var hins vegar óháð myndunaraðstæðum.

Myosin was extracted from Atlantic Cod (Gadus Morhua) using different methods resulting in small aggregates of pure myosin. These aggregates consisted of between 8 and 20 myosin molecules and were relatively stable at low temperatures (T<20°C) in dilute (C<5g/L) solutions containing 0.5M KCl in the pH range 6.0-8.0. At higher concentrations precipitation or gelation was observed. Heat induced aggregation at low concentrations was studied using turbidimetry and light scattering. In most cases the aggregation stagnated at longer heating times, but in some cases the aggregation continued until it led to precipitation of large flocs. Cooling led to further growth of the aggregates, which was, however, reversed upon heating. The structure of the aggregates was determined after cooling and dilution using static and dynamic light scattering. Self-similar aggregates were observed, characterized by a fractal dimension of 2.2. The size of the aggregates formed after extensive heating increased with increasing temperature (30-70°C), decreasing pH (8.0-6.0) and increasing protein concentration (0.4-3g/L), but the structure of large aggregates was independent of the conditions.

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