FUNCTIONAL-CHANGES OF DEXTRAN-MODIFIED ALKALINE PROTEINASE FROM ALKALOPHILIC BACILLUS SP

A serine alkaline proteinase (EC 3.4.21.62) from Bacillus sp. (ALPase I) was modified with the 2,4-dialdehyde derivative of clinical dextran (dialdehyde dextran). The modified preparation was purified using an ion-exchange column and gel filtration. The modified enzyme contained 75% carbohydrate by weight. The isoelectric point (pI) of ALPase I was converted from 8.2 to approximately 5.0 by this modification. The spe cific activity of the dextran-modified ALPase I was 56% of that of the native enzyme when milk casein was used as a substrate. It also had s ome superior characteristics: the thermostability of the modified enzy me at pH 10.0 was about 10-15 degrees C higher than that of control. I n organic solvents such as n-hexane, benzene, and toluene, the hydroly sis reaction of the modified ALPase I for the fluorogenic substrate, l -L-prolyl-L-phenylalanyl-4-methylcoumaryl-7-amide (Suc-Ala-Ala-Pro-Phe -MCA), was several times higher than that of the native. This modifica tion greatly improved the stability of ALPase I against nonionic and a nionic surfactants. After exposure to lauryl benzene sulfonate and sod ium lauryl sulfonate the modified enzyme retained over 95 and 90% of i ts activity, respectively, but the native enzyme lost its activity. We conclude that modification of serine proteinases with dialdehyde-dext ran might be a useful method for improving enzyme character for enzyme technology.