ISSN:
1432-0614
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Summary Cellobiose-grown cells of Candida wickerhamii transported cellobiose as glucose by a glucose-proton symport after previous hydrolysis of the disaccharide by an exocellular β-glucosidase. Both the symport and the β-glucosidase were subject to glucose-induced repression and inactivation while glucose also acted as a competitive inhibitor of the enzyme (K i 0.3 mM). Under conditions of glucose repression glucose was transported by facilitated diffusion. Cellobiose acted as a competitive inhibitor of the latter (K i 75 mM) and is possibly a low-affinity substrate, while it inhibited non-competitively the glucoseproton symport (K i 80 mM). The affinity of cellobiose for the cell-bound β-glucosidase was much higher (K m 4.2 mM) than for the purified enzyme as reported by others (K m 67–225 mM). Ethanol reversibly inhibited the two glucose transport systems with exponential non-competitive kinetics. The minimum inhibitory concentrations were about 3% and 4% (w/v) for facilitated diffusion and proton symport while the respective exponential inhibition constants were 0.58 l mol-1 and 1.65 l mol-1. Ethanol affected the β-glucosidase in a complex way, a major effect was deviation from Michaelis-Menten kinetics for ethanol concentrations higher than 4% (w/v), the Hill coefficient increasing up to 1.8 at 6% (w/v) ethanol.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00253662
