Presence and activity of the hexosemonophosphate shunt in a marine pennate chemoorganotrophic diatom, Nitzschia alba, clone Link 001
A commonly occurring chemoorganotrophic diatom, Nitzschia alba, clone Link 001, stores primarily fatty acids and utilizes the hexose monophosphate shunt as a major pathway in hexose oxidation. The presence and activity of this pathway in exponentially growing N. alba was demonstrated by the growth on potassium gluconate as a sole carbon source, in vitro assay of 6-phosphogluconate dehydrogenase (EC 1.1.1.44), and in vivo radiorespirometric evaluation using [14C]-glucose or -gluconate. Radiorespirometry demonstrated that the hexose monophosphate and Embden–Meyerhoff–Parnas pathways account for 46 and 54% of hexose oxidation, respectively. The predominance of fatty acid storage plus the probable utilization of some C4–C5 hexose monophosphate intermediates in biosynthetic activities support the relatively high hexose monophosphate activity in these exponentially growing cells. Radiorespirometric values are supported by the absence of Entner–Doudoroff activity as determined by the lack of 2-keto-3-deoxy-6-phosphogluconate aldolase (EC 4.1.2.14) and 6-phosphogluconate dehydratase (EC 4.2.1.14) activity.