Description:
<jats:p>Sorbose-transport in Neurospora has been investigated further. Methods and results were as follows:</jats:p>
<jats:p>Conidia pregerminated with fructose were incubated with increasing amounts of <jats:sup>14</jats:sup>C-labelled sorbose, their radioactivity was measured by millipore-filter technique. Sorbose uptake followed Michaelis-Menten kinetics, with K<jats:sub>m</jats:sub> = 5.1 ± 1.2 mM and V<jats:sub>max</jats:sub>=0.16 ± 0.05 mg sorbose/mg dry weight/minute. It was inhibited slightly by addition of fructose, and strongly by addition of glucose; the exact type of inhibition was concentration dependent.</jats:p>
<jats:p>Ungerminated conidia or pregerminated conidia were incubated with <jats:sup>14</jats:sup>C-labelled sorbose. A base level of sorbose uptake by ungerminated conidia, and an increasing uptake with increasing pregermination time of the conidia was found; the uptake was proportional to germ-tube length.</jats:p>
<jats:p>Supernatants of ungerminated or germinated conidia were checked for sugars related to sorbose by enzymatic and bio-assays. The results were negative.</jats:p>
<jats:p>Radiopaperchromatography of aqueous extracts of incubated conidia revealed that sorbose as opposed to fructose is not phosphorylated during uptake, but accumulated as the pure sugar inside the cells. Ca. 90% of the fructose but barely 7% of sorbose taken up is transformed into a water insoluble form after 60 minutes incubation of the conidia.</jats:p>
<jats:p>Conidia incubated with labelled sorbose were treated with unlabelled sorbose or Na-azide. The accumulated labelled sorbose was driven out by both treatments (with sorbose ca. 65% with Naazide ca. 80% after 60 minutes).</jats:p>
<jats:p>The data support the hypothesis proposed earlier<jats:sup>1</jats:sup> that sorbose is taken up into conidia of Neurospora crassa by means of active transport, mediated by an inducible enzymatic system of the permease-type.</jats:p>