d -Mannitol Metabolism by Aspergillus candidus

Abstract

Pathways of mannitol biosynthesis and utilization in Aspergillus candidus NRRL 305 were studied in cell-free extracts of washed mycelia prepared by sonic and French pressure cell treatments. A nicotinamide adenine dinucleotide-linked mannitol-1-phosphate (M1P) dehydrogenase was found in French pressure cell extracts of d -glucose-grown cells, whereas a specific mannitol-1-phosphatase was present in extracts prepared by both methods. The existence of these two enzymes indicated that mannitol may be synthesized in this organism by the reduction of fructose-6-phosphate. A specific nicotinamide adenine dinucleotide phosphate-linked mannitol dehydrogenase was also identified in both extracts. This enzyme may have been involved in mannitol utilization. However, the level of the mannitol dehydrogenase appeared to be substantially reduced in extracts from mannitol-grown cells, whereas the level of M1P dehydrogenase was increased. A hexokinase has been identified in this organism. Fructose-6-phosphatase, glucose isomerase, and mannitol kinase could not be demonstrated.