问题描述：
英语翻译
PFA and other pyrococcal amylolytic enzymes.Koch et al.(24) described an extracellular a-amylase activity present in the supernatants of P.furiosus cultures.The activity they de¬scribed corresponded to two starch-degrading protein bands of 96 and 136 kDa in native PAGE.It is not clear from their work if these two bands correspond to one or two separate enzymes and if the 96-kDa band is similar to the enzyme described here.It is unlikely that these bands are the P.furiosus amylopullu-lanase (9,16),since no pullulanase activity was detected in their enzyme preparation (24).Another member of the order Thermococcales,T.profundus,optimally growing at 80°C,pro¬duced two extracellular amylases,S and L (12).With a molec¬ular mass of 42 kDa in SDS-PAGE,amylase S is optimally active at pH 5.5 to 6.0 and 80°C and does not require Ca2+ for its activity.While no sequence is available for amylase S,its catalytic properties suggest that it is the T.profundus counter¬part of PFA.Amylase L,a larger enzyme,could correspond to the P.furiosus 136-kDa amylolytic enzyme detected by Koch et al.(24).
A P.woesei extracellular a-amylase (PWA) has been purified and characterized by Koch et al.(23).PFA and PWA are optimally active under the same conditions of pH and temper¬ature and have similar resistance to thermal inactivation.Al¬though PWA was described as a 70,000-MW enzyme,as indi¬cated from migration in SDS-PAGE,it could correspond to a dimeric enzyme showing aberrant behavior under these elec-trophoresis conditions,a behavior similar to that observed with PFA.PFA and PWA seem to differ in two aspects:(i) PWA shows almost six-times-lower specific activity than PFA (667 versus 3,900 U mg_1),and (ii) their amino acid compositions seem to be different (in particular,PFA contains half the threonine residues present in PWA).P.furiosus and P.woesei amylopullulanases were also shown to be significantly different in a few aspects (16).Although these two organisms are con¬sidered to be very closely related,they still contain quite dif¬ferent enzymes.
PFA is the first archaeal amylolytic enzyme described that belongs to the a-amylase family.The characterization of ex¬tracellular a-amylases with similar properties from other hy-perthermophilic archaea (12,23) suggests that these enzymes also belong to the a-amylase family and that this enzyme family is widespread among the three kingdoms.
PFA and other pyrococcal amylolytic enzymes.Koch et al.(24) described an extracellular a-amylase activity present in the supernatants of P.furiosus cultures.The activity they de¬scribed corresponded to two starch-degrading protein bands of 96 and 136 kDa in native PAGE.It is not clear from their work if these two bands correspond to one or two separate enzymes and if the 96-kDa band is similar to the enzyme described here.It is unlikely that these bands are the P.furiosus amylopullu-lanase (9,16),since no pullulanase activity was detected in their enzyme preparation (24).Another member of the order Thermococcales,T.profundus,optimally growing at 80°C,pro¬duced two extracellular amylases,S and L (12).With a molec¬ular mass of 42 kDa in SDS-PAGE,amylase S is optimally active at pH 5.5 to 6.0 and 80°C and does not require Ca2+ for its activity.While no sequence is available for amylase S,its catalytic properties suggest that it is the T.profundus counter¬part of PFA.Amylase L,a larger enzyme,could correspond to the P.furiosus 136-kDa amylolytic enzyme detected by Koch et al.(24).
A P.woesei extracellular a-amylase (PWA) has been purified and characterized by Koch et al.(23).PFA and PWA are optimally active under the same conditions of pH and temper¬ature and have similar resistance to thermal inactivation.Al¬though PWA was described as a 70,000-MW enzyme,as indi¬cated from migration in SDS-PAGE,it could correspond to a dimeric enzyme showing aberrant behavior under these elec-trophoresis conditions,a behavior similar to that observed with PFA.PFA and PWA seem to differ in two aspects:(i) PWA shows almost six-times-lower specific activity than PFA (667 versus 3,900 U mg_1),and (ii) their amino acid compositions seem to be different (in particular,PFA contains half the threonine residues present in PWA).P.furiosus and P.woesei amylopullulanases were also shown to be significantly different in a few aspects (16).Although these two organisms are con¬sidered to be very closely related,they still contain quite dif¬ferent enzymes.
PFA is the first archaeal amylolytic enzyme described that belongs to the a-amylase family.The characterization of ex¬tracellular a-amylases with similar properties from other hy-perthermophilic archaea (12,23) suggests that these enzymes also belong to the a-amylase family and that this enzyme family is widespread among the three kingdoms.
问题解答：
我来补答展开全文阅读