Chemical Modification of Taka-Amylase A

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Abstract
In a previous paper (1) the author reported the chemical modifications of Taka-amylase A (TAA) with fluorodinitrobenzene and dinitrobenzene sulfonate. From these results, it was suggested that e-amino groups of lysine residues of the protein do not play any essential role for the emergence of amylase activity, but some special phenolic groups of tyrosine residues are more closely connected with the activity. In the present study, p-phenylazobenzoyl (PhAB) chloride was chosen as an acylating reagent to modify TAA, because PhAB compounds exhibit characteristic absorption maxima at 430 and 330 mµ, and the number of the reagent introduced into the protein can be determined with great ease. Recently, it was confirmed in our laboratory that crystalline TAA is able to hydrolyse ai-phenylmaltoside and p-nitrophenyl-α-maltoside to form maltose and corresponding phenols when considerably high concentration of the enzyme are used and this α-phenylmaltosidase activity is an intrinsic property of the TAA protein itself (2). In tne present study, the changes of activities of the enzyme by acylation with PhAB chloride were determined using amylose, maltotetraose, α-phenyl-maltoside and p-nitrophenyl-α-maltoside as substrates, and it was found that the amylase activity is almost lost by introduction of 1 mole of PhAB residue into 1 mole of the amylase protein, while α-phenylmaltosidase activity increases about 2.5 fold, and it was suggested that PhAB residue may be combined with a special group situated in the vicinity of the active center.

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