Constitutive and Induced Trehalose Transport Mechanisms in Spores of the Fungus Myrothecium verrucaria

Abstract

Trehalose is absorbed by two distinct systems—one constitutive, the other induced by turanose and to a lesser extent by nigerose but not by trehalose. The constitutive system is apparently mediated by a surface trehalase; the induced system has the characteristics of a permease. The specificity of the induced system is apparently limited to the α glucosyl-glucose or glucosyl-fructose linkage, because absorption of kojibiose, nigerose, maltose, isomaltose, turanose, sucrose, and melezitose, in addition to that of trehalose, was increased. Absorption of β-linked or of galactose-containing disaccharides was not increased. The constitutive and induced trehalose-absorbing systems differ in their activity, specificity, lability to acid treatment, effects of substrate concentration, and p H optima. Both systems require oxygen, and no marked differential effects of inhibitors were observed. The activity of the induced system is proportional to log turanose concentration (from about 1 to 300 μg/ml), and is an approximate linear function of time of exposure (from about 1 to 50 min). Accumulation of trehalose occurred against a concentration gradient in both systems but particularly in the induced. No leakage was observed. The activity of the induced system declined slowly upon removal of the inducer. Accumulated trehalose is metabolized after activation by azide as are the endogenous trehalose reserves. The accumulated trehalose appears to enter the endogenous trehalose pool found in these spores, although some data suggest it may be more accessible. Respiratory data indicate that absorbed trehalose is available for metabolism while in transit from the external membrane to the internal pool.