Utilize este identificador para referenciar este registo:
https://hdl.handle.net/1822/7977
Título: | Stimulation of zero-trans rates of lactose and maltose uptake into yeasts by preincubation with hexose to increase the adenylate energy charge |
Autor(es): | Guimarães, Pedro M. R. Multanen, Jyri-Pekka Domingues, Lucília Teixeira, J. A. Londesborough, John |
Data: | Mai-2008 |
Editora: | American Society for Microbiology (ASM) |
Revista: | Applied and Environmental Microbiology |
Citação: | "Applied and Environmental Microbiology". ISSN 0099-2240. 74:10 (May 2008) 3076-3084. |
Resumo(s): | Initial rates of sugar uptake (zero-trans rates) are often measured by incubating yeast cells with radiolabeled sugars for 5 to 30 s and determining the radioactivity entering the cells. The yeast cells used are usually harvested from growth medium, washed, suspended in nutrient-free buffer, and stored on ice before they are assayed. With this method, the specific rates of zero-trans lactose uptake by Kluyveromyces lactis or recombinant Saccharomyces cerevisiae strains harvested from lactose fermentations were three- to eightfold lower than the specific rates of lactose consumption during fermentation. No significant extracellular β-galactosidase activity was detected. The ATP content and adenylate energy charge (EC) of the yeasts were relatively low before the [14C]lactose uptake reactions were started. A short (1- to 7-min) preincubation of the yeasts with 10 to 30 mM glucose caused 1.5- to 5-fold increases in the specific rates of lactose uptake. These increases correlated with increases in EC (from 0.6 to 0.9) and ATP (from 4 to 8 µmol·g dry yeast–1). Stimulation by glucose affected the transport Vmax values, with smaller increases in Km values. Similar observations were made for maltose transport, using a brewer's yeast. These findings suggest that the electrochemical proton potential that drives transport through sugar/H+ symports is significantly lower in the starved yeast suspensions used for zero-trans assays than in actively metabolizing cells. Zero-trans assays with such starved yeast preparations can produce results that seriously underestimate the capacity of sugar/H+ symports. A short exposure to glucose allows a closer approach to the sugar/H+ symport capacity of actively metabolizing cells. |
Tipo: | Artigo |
URI: | https://hdl.handle.net/1822/7977 |
DOI: | 10.1128/AEM.00188-08 |
ISSN: | 0099-2240 |
Arbitragem científica: | yes |
Acesso: | Acesso aberto |
Aparece nas coleções: | CEB - Publicações em Revistas/Séries Internacionais / Publications in International Journals/Series |
Ficheiros deste registo:
Ficheiro | Descrição | Tamanho | Formato | |
---|---|---|---|---|
Guimaraes2_AEM[2].pdf | 760,1 kB | Adobe PDF | Ver/Abrir |