Glucose tolerance, an enzymatic performance in the presence of glucose, was improved with Geobacillus thermoglucosidasius oligo-1,6-glicosidase (GTAGL) by site-directed mutagenesis. The quadruple mutant of GTAGL (qGTAGL: M203W/Q216E/G259E/R298I) produced by this work resulted in an increase of the glucose tolerance. Although GTAGL lost its enzyme activity in the presence of 2.2% glucose, qGTAGL retained the activity in the presence of 2.7% glucose. Notably, enzymatic properties including thermostability and optimal temperature were not severely affected by the mutations.
Pseudomonas putida ATCC12633 and some other fluorescent Pseudomonas strains utilized 1,4diguanidinobutane (arcaine) and its homologues with 3~7 methylene groups as sole nitrogen sources. The P. putida strain produced a novel enzyme which hydrolyzed 1,4-diguanidinobutane to agmatine and urea; diguanidinobutane amidinohydrolase (EC class 3.5.3.) was proposed as the name for this enzyme. This enzyme hydrolyzed diguanidinoalkanes with 3~10 methylene groups; higher reaction rates were observed with 1,4-diguanidinobutane, 1,5-diguanidinopentane, and 1,6-diguanidinohexane. The enzyme was also active toward agmatine, although the rate was below 1 %of that toward 1,4diguanidinobutane, and it was suggested to catalyze the hydrolysis of the higher homologues of agmatine at higher rates. The enzyme was induced by a,co-diguanidinoalkanes with 3~7 methylene groups. The substrate specificities of the enzymes individually induced by the diguanidinoalkanes with 3~7 methylene groups were very close to each other. It was then concluded that only one enzyme was produced to catalyze the initial step of the degradation of the diguanidinoalkanes commonly. Diguanidinobutane* (arcaine, A^TV'-diamidinoputrescine), which was found in a marine mollusk, Area noae,l) and diguanidinopentane (audouine, N,N'-diamidinocadaverine) occur in some invertebrates2'3) and plants.4) A plant, Lathyrus sativus*] and a leech,
α-1,6-Glucosidase (isomaltase) belongs to glycoside hydrolase (GH) families 13 and 31. Genes encoding 3 isomaltases belonging to GH family 13 were cloned from filamentous fungi, Aspergillus oryzae (agl1), A. niger (agdC), and Fusarium oxysporum (foagl1), and expressed in Escherichia coli. The enzymes hydrolyzed isomaltose and α-glucosides preferentially at a neutral pH, but did not recognize maltose, trehalose, and dextran. The activity of AgdC and Agl1 was inhibited in the presence of 1 % glucose, while Foagl1 was more tolerant to glucose than the other two enzymes were. The three fungal isomaltases did not show transglycosylation when isomaltose was used as the substrate and a similar result was observed for AgdC and Agl1 when p-nitrophenyl-α-glucoside was used as the substrate.
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