Hydrolysis Activity of ${\alpha}-Galactosidase$ from Bacillus licheniformis

Bacillus licheniformis로부터 생산된 ${\alpha}-Galactosidase$의 가수분해 활성

The maximum productivity of ${\alpha}-galactosidase,$ capable of hydrolyzing completely ${\alpha}-D-l,6-galactopyranosyl$ linkages within oligomeric substrates such as melibiose, raffinose and stachyose to liberate galactose residue, was reached to 718 mU/ml in the culture filtrate of Bacillus licheniformis at death phase. The ${\alpha}-galactosidase$ was identified to show different efficiencies for hydrolyzing the ${\alpha}-galactooligosaccharides$ according to analysis of reaction products by both TLC and quantification of the liberated reducing sugars. The enzyme was active on ${\alpha}-galactooligosaccharides$ in the order of melibiose, raffinose, and stachyose. Though the hydrolyzing activity of enzyme was faintly inhibited by reaction products such as galactose, glucose and sucrose with amounts of five folds more than the added substrates (20 mM), the largest inhibition of enzyme activity was caused by galactose among the end products. Unknown compound, which migrated slower than melibiose on TLC, was detected during hydrolysis reaction of melibiose, suggesting that the ${\alpha}-galactosidase$ has a glycosyl transferase activity. In addition, the enzyme was able to hydrolyze efficiently raffinose and stachyose existed in the soluble extract of soybean meal.

[ ${\alpha}$ ]-갈락토올리고 당인 melibiose, raffinose와 stachyose의 ${\alpha}-1,6$으로 결합된 D-galactosyl 잔기를 완전히 가수분해하는 것으로 확인된 Bacillus licheniformis YB-42의 ${\alpha}-galactosidase$는 사멸기에 도달하였을 때 배양상등액에서 최대활성을 보였다. ${\alpha}$-갈락토올리고 당의 가수분해 정도를 TLC와 환원당 생성량으로 분석한 결과, ${\alpha}-galactosidase$는 melibiose, raffinose, stachyose 순서로 가수분해 활성이 높았다. 반응산물인 당을 첨가하여 반응하였을 때 첨가 된 반응산물에 따라 가수분해 활성의 저해정도가 다르게 나타났으며, galactose에 의한 저해도가 가장 높았다. 첨가된 당의 농도 (20 mM)가 기질과 동일할 때는 가수분해 활성의 저해도가 미미하였으며 5배 농도로 첨가하였을 때도 가수분해 활성의 저해정도가 높지 않았다. 한편 소량의 효소로melibiose를 가수분해 하였을 때 반응초기에 TLC 상에서 기질보다 이동도가 낮은 물질이 생성되었으며, 이로보아 B. licheniformis YB-42의 ${\alpha}-galactosidase$는 당 전이활성을 갖는 것으로 여겨진다. 또한 대두분 추출액을 ${\alpha}-galactosidase$로 처리한 후 최종 반응산물을 분석한 결과, 대두분에 존재하는 raffinose와 stachyose가 완전히 가수분해 되었다.