TREHALASES AND TREHALOSE HYDROLYSIS IN FUNGI

The simultaneous presence of two different trehalose-hydrolysing activ ities has been recognised in several fungal species. While these enzym es, known as acid and neutral trehalases, share a strict specificity f or trehalose, they are nevertheless rather different in subcellular lo calisation and in several biochemical and regulatory properties. The f unction of these apparently redundant activities in the same cell was not completely understood until recently. Biochemical and genetic stud ies now suggest that these enzymes may have specialised and exclusive roles in fungal cells. It is thought that neutral trehalases mobilise cytosolic trehalose, under the control of developmental programs, chem ical and nutrient signals, or stress responses. On the other hand, aci d trehalases appear not to mobilise cytosolic trehalose, but to act as 'carbon scavenger' hydrolases enabling cells to utilise exogenous tre halose as a carbon source, under the control of carbon catabolic regul atory circuits. Although much needs to be learned about the molecular identity of trehalases, it seems that in fungi at least one class of a cid trehalases evolved independently from the other trehalases.