Examination of the active sites of human salivary α-amylase (HSA)
作者:Lili Kandra、Gyöngyi Gyémánt
DOI:10.1016/s0008-6215(00)00221-4
日期:2000.11
The action pattern of human salivary amylase (HSA) was examined by utilising as model substrates 2-chloro-4-nitrophenyl (CNP) beta -glycosides of maltooligosaccharides of dp 4-8 and some 4-nitrophenyl (NP) derivatives modified at the nonreducing end with a 4,6-O-benzylidene (Bnl) group. The product pattern and cleavage frequency were investigated by product analysis using HPLC. The results revealed that the binding region in HSA is longer than five subsites usually considered in the literature and suggested the presence of at least six subsites; four glycone binding sites (- 4, - 3, - 2, - 1) and two aglycone binding sites (+ 1, + 2). In the ideal arrangement, the six subsites are filled by a glucosyl unit and the release of maltotetraose (G(4)) from the nonreducing end is dominant. The benzylidene group was also recognisable by subsites (- 3) and ( - 4). The binding modes of the benzylidene derivatives indicated a favourable interaction between the Bnl group and subsite (- 3) and an unfavourable one with subsite (- 4). Thus, subsite (- 4) must be more hydrophylic than hydrophobic. As compared with the action of porcine pancreatic alpha -amylase (PPA) on the same substrates, the results showed differences in the three-dimensional structure of active sites of HSA and PPA. (C) 2000 Elsevier Science Ltd. All rights reserved.
Chemoenzymatic preparation of 2-chloro-4-nitrophenyl β-maltooligosaccharide glycosides using glycogen phosphorylase b
作者:Lili Kandra、Gyöngyi Gyémánt、András Lipták
DOI:10.1016/s0008-6215(98)00324-3
日期:1999.1
In the present work, we aimed to develop a new chemoenzymatic procedure for the synthesis of beta-maltooligosaccharide glycosides. The primer in the enzymatic reaction was 2-chloro-4-nitrophenyl beta-maltoheptaoside (G(7)-CNP), which was synthesised from beta-cyclodextrin (beta-CD) using a very convenient chemical method [E. Farkas, L. Janossy, J. Harangi, L. Kandra, A. Liptak, Carbohydr. Res., 303 (1997) 407-415]. Shorter chain length CNP-maltooligosaccharides in the range of dp 3-6 were prepared using rabbit skeletal muscle glycogen phosphorylase b (EC 2.4.1.1). Detailed enzymological investigations revealed that the conversion of G(7)-CNP was highly dependent on the conditions of phosphorolysis. A 100% conversion of G(7)-CNP was achieved during 10 min in 1 M phosphate buffer (pH 6.8) at 30 degrees C with the tetramer glycoside (77%) as the main product. Phosphorolysis at 10 degrees C for 10 min resulted in 89% conversion and G(4), G(5)-, and G(6)-CNP oligomers were detected in the ratio of 39:26:34%, respectively. The reaction pattern was investigated using an HPLC system. The preparative scale isolation of G(3-->6)-CNP glycosides was achieved by size-exclusion column chromatography (SEC) on Toyopearl HW-40 matrix. The productivity of the synthesis was improved by yields of up to 70-75%. (C) 1999 Elsevier Science Ltd. All rights reserved.
Synthesis of chromogenic substrates of α-amylases on a cyclodextrin basis
transformed into 4-nitrophenyl and 2-chloro-4-nitrophenyl β-glycosides. From the 4-nitrophenyl glycosides 4,6-O-benzylidene derivatives were prepared, which were used together with the free glycosides as substrates of porcine pancreatic α-amylase. One-pot acetylation and subsequent partial acetolysis of cyclodextrins resulted in the peracetylated maltooligomers (dp 3–8), which were transformed into 4-nitrophenyl