No abstract

No abstract

whilst the organism was in the stationary phase but exoglucanase activityy decreased sharply at the onset of the stationary phase'. Addition of the protease inhibitor phenylmethylsulphonyl fluoride (PMSF) towards the end of growth produced complete protection toward protease inactivation, exoglucanase being stabilized even in prolonged stationary phase. The stability of exoglucanase in the presence or absence of mycelium, with and without PMSF addition, showed that endogenous cell-free and cell-associated proteases weree responsible for exoglucanase inactivation i n the stationary phase. Inactivation of exoglucanase depended on the physiological stage of the cultures, the enzyme remaining stable as long as the culture was in an active growth phase. R6sum6Production et stabilisation de cellulases de Trichoderma reesei La production d'exoglucanase et d'endoglucanase dans les cultures de T. reesei QM 9414 en milieu non renouvel6 est associ6e ~t la croissance tant du lactose que du jus d'extraction de la pulpe de betterave. L'endo-glucanase reste stable tant que le microorganisme est darts sa phase stationnaire de croissance tandis que l'activit6 exoglucanasique d6croit rapidement d6s le d6but de cette phase stationnaire. L'ajour du fluorure de phenylmethylsulfonate (PMSF), un inhibiteur prot6olytique, vers la fin de la croissance a exerc6 une protection compl6te contre l'inactivation par la prot6ase: l'exoglucanase 6tait prot6g6e dans ces conditions m6me en phase stationnaire prolong6e. La stabilit6 de l'exoglucanase en pr6sence ou en absence de mycelium, avec ou sans ajout de PMSF d6montre la responsabilit6 des exo-prot6ases endog~nes solubles et de prot6ases associ6es aux cellules dans l'inactivation de l'exoglucanase dans la phase stationnaire. L'inactivation de l'exoglucanase d6pend de l'6tat physiologique des cultures. En effet, l'enzyme reste stable aussi longtemps que la culture est en phase active de croissance. Resumen Producci6n y estabilizaci6n de celulasas de Trichoderma reeseiLa producci6n de exoglucanase y endoglucanasa de T. reesei QM 9414 en cultivo pot lotes en medios con tactosa y coseta agotada de remolacha como fuentes de carbono, fue asociada al crecimiento. La endoglucanasa permaneci6 estable en fase estacionaria, pero la actividad de exoglucanase disminuy6 dr~sticamente al entrar el cultivo en dicha fase. La adici6n del inhibidor de proteasas PMSF hacia el final de la fase de crecimiento provoc6 la total inactivaci6n de las proteasas producidas, logrfindose estabilizar la exoglucanasa at~n en prolongada fase estacionaria. Se analiz6 la estabilidad de exoglucanasa en presencia y ausencia de micelio, con y sin adici6n de PMSF; los resultados muestran que proteasas endogenas extracelulares y asociadas a la c61ula son responsables de la inestabilidad de la exoglucanasa en fase estacionaria. La inactivaci6n de la exoglucanasa depende del estado fisiol6gico del cultivo, ya que la enzima permanece estable mientras el cultivo se encuentra en crecimiento.

No abstract

Fermentable sugars from beet pulp were obtained in a two‐stage hydrolytic process. The first stage involved mild acid treatment to hydrolyze the hemicellulose, producing a pentose‐rich syrup and a cellulose‐rich fraction. The second stage was the enzymic saccharification of the cellulose fraction with fungal cellulases to produce a glucose‐rich syrup. The acid hydrolysis stage was evaluated to optimize the type of acid, acid concentration, temperature and reaction time. Solubilization was markedly temperature‐dependent, whereas the specificity of hemicellulose degradation depended on the type of acid utilized. The effects of different reaction times, enzyme‐to‐substrate ratios and particle sizes on the enzymic stage were studied. Both saccharification rate and the extent of final conversion to glucose were markedly affected by the enzyme‐to‐substrate ratio. Sugars recovered from the enzymic degradation of cellulose were partially fermented by Saccharomyces cerevisiae ATCC 4126.