Browsing by Author "Chang, LF"

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Characterization of an isozyme of beta-glucosidase from sweet almond
(1997-02-01)
Li, YK
;
Chang, LF
;
Shu, HH
;
Chir, J
;
交大名義發表
A sweet almond beta-glucosidase (EC 3.2.1.21) isozyme was purified from commercial crude product. The process of purification consisted of a Protein-Pak Q anion exchange chromatography following by a Superdex 75 HR gel filtration separation. The purified enzyme is a monomeric glycoprotein with molecular weight of 58 kDa and pI = 4.55 which is distinguished from reported isozymes. The enzyme has a pH optimum in the range of 5.2-5.6 when p-nitrophenyl-beta-D-glycopyranosides are used as substrate and is stable up to 50 degrees C at that pH range. The purified protein also exhibits profound beta-galactosidase and alpha-L-arabinosidase activity. The study of substrate specificity revealed that lacking of hydroxymethyl group at C-5 of glycosides resulted in higher affinity for substrate binding to enzyme, whereas the chemical step of hydrolysis (k(cat)) was prevented significantly. The pH activity profile displayed a bell-shaped curve for all measured p-nitrophenyl-beta-D-glycopyranosides with apparent pK(1) and pK(2) values of 4.4-4.7 and 6.2-6.4, respectively. This isozyme was strongly inhibited by delta-gluconolactone (K-i = 160 mu M) and 4-phenylimidazole (K-i = 17.8 mu M) reversibly at pH 6.2. Among the tested glycoses, the binding affinity of N-acetyl-beta-D-glucosamine to the enzyme (K-i = 52 mM) was 6 times stronger than that of glucose and its epimers.
Characterization of an isozyme of beta-glucosidase from sweet almond
(1997-02-01)
Li, YK
;
Chang, LF
;
Shu, HH
;
Chir, J
;
應用化學系
A sweet almond beta-glucosidase (EC 3.2.1.21) isozyme was purified from commercial crude product. The process of purification consisted of a Protein-Pak Q anion exchange chromatography following by a Superdex 75 HR gel filtration separation. The purified enzyme is a monomeric glycoprotein with molecular weight of 58 kDa and pI = 4.55 which is distinguished from reported isozymes. The enzyme has a pH optimum in the range of 5.2-5.6 when p-nitrophenyl-beta-D-glycopyranosides are used as substrate and is stable up to 50 degrees C at that pH range. The purified protein also exhibits profound beta-galactosidase and alpha-L-arabinosidase activity. The study of substrate specificity revealed that lacking of hydroxymethyl group at C-5 of glycosides resulted in higher affinity for substrate binding to enzyme, whereas the chemical step of hydrolysis (k(cat)) was prevented significantly. The pH activity profile displayed a bell-shaped curve for all measured p-nitrophenyl-beta-D-glycopyranosides with apparent pK(1) and pK(2) values of 4.4-4.7 and 6.2-6.4, respectively. This isozyme was strongly inhibited by delta-gluconolactone (K-i = 160 mu M) and 4-phenylimidazole (K-i = 17.8 mu M) reversibly at pH 6.2. Among the tested glycoses, the binding affinity of N-acetyl-beta-D-glucosamine to the enzyme (K-i = 52 mM) was 6 times stronger than that of glucose and its epimers.
New imidazoles as probes of the active site topology and potent inhibitors of beta-glucosidase
(1998-03-01)
Li, YK
;
Hsu, HS
;
Chang, LF
;
Chen, G
;
應用化學系
Series of 4-arylimidazoles, omega-N-acylhistamines and 4-(omega-phenylalkyl) imidazoles were synthesized in order to probe the active site topology of sweet almond beta-glucosidase. These imidazole derivatives were shown to be very powerful competitive inhibitors. Among the 20 tested compounds, omega-N-benzoylhistamine and 4-(3'-phenylpropyl)imidazole are the most potent inhibitors of the enzyme, with pH-independent K-i values of 0.06 and 0.07 mu M, respectively, The inhibition of 4-(omega-phenylalkyl)imidazoles exhibited an interesting trend as to K-i values: 4-phenylimidazole (6.6 mu M)>4-benzylimidazole (1.4 mu M)>4-(2'-phenylethyl)imidazole (0.82 mu M)>4-(3'-phenylpropyl)imidazole (0.07 mu M)<4-(4'-phenylbutyl)imidazole (0.13 mu M)<4-(5'-phenylpentyl)imidazole (0.3 mu M), This revealed that the imidazole and aryl binding sites (which result from favorable interactions within the corresponding glycone and aglycone binding subsites) are separated by the optimal distance equivalent to the length of a -CH2-CH2-CH2-group, Substitutions of the phenyl moieties of 4-phenylimidazole and 4-benzoylhistamine result in weaker inhibition, These classes of imidazoles are particularly powerful inhibitors of sweet almond beta-glucosidase.
Polling deregistration for unlicensed PCS
(1996-05-01)
Noerpel, AR
;
Chang, LF
;
Lin, YB
;
資訊工程學系
;
Department of Computer Science
This paper describes a polling deregistration protocol for a wireless access communications network which would support interoperability between licensed personal communications services (PCS) and unlicensed-PCS (UPCS), We show how the protocol can be efficiently implemented in the personal access communications system (PACS) for licensed PCS and in the PACS-Unlicensed Version B (PACS-UB), An analytical model is proposed to analyze the performance of the polling protocol, A cost function is derived, which can be used to estimate the optimal polling frequency.
Polling deregistration for unlicensed PCS
(1996-05-01)
Noerpel, AR
;
Chang, LF
;
Lin, YB
;
資訊工程學系
;
Department of Computer Science
This paper describes a polling deregistration protocol for a wireless access communications network which would support interoperability between licensed personal communications services (PCS) and unlicensed-PCS (UPCS), We show how the protocol can be efficiently implemented in the personal access communications system (PACS) for licensed PCS and in the PACS-Unlicensed Version B (PACS-UB), An analytical model is proposed to analyze the performance of the polling protocol, A cost function is derived, which can be used to estimate the optimal polling frequency.