Presence and activity of the hexosemonophosphate shunt in a marine pennate chemoorganotrophic diatom, Nitzschia alba, clone Link 001.

Abstract

A commonly occurrring 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 Enter-Doudoroff activity as determined by the lace of 2-keto-3-deoxy-6-phosphogluconate aldolase (EC 4.12.14) and 6-phosphogluconate dehydratase (EC 4.2.1.14) activity.