It has been found that Ser His could cleave bovine serum albumin(BSA), with the most suitable pH around 6.0. The kinds of buffers have different influences on the cleavage activity. The phosphate buffer and BR buffer are the most effective. The hydroxyl group of the serine residue is the essential functional group for the cleavage, while the amide bond, imidazole, and carboxyl group of Ser His increase the cleavage activity.
The effects of the amino, hydroxyl, imidazole and carboxyl groups of Ser His on DNA cleavage reaction were studied. It was found that the amino and hydroxyl groups were essential for the DNA cleavage activity of Ser His, and that anyone of them blocked would result into the loss of cleavage activity. The carboxyl group was not the necessary group. The presence of the imidazole group would enhance the cleavage activity. However, the histidyl serine dipeptide, as the formula isomer of Ser His with the inverse peptide sequence, could not cleave DNA at all. Based on the above experimental results, a presumed cleavage mechanism of Ser His on DNA was proposed. [WT5HZ]
Two imidazolium-bridged cyclodextrin dimers 3a and 3b were prepared by reacting 6-deoxy-6-N-imidazolyl-β-CD (2) with bis(bromomethyl)benzene. The catalytic properties of 2, 3a and 3b in the hydrolytic cleavage of p-nitrophenyl alkanoates, in the form of acetate (PNPA) , butanoate (PNPB) , hexanoate (PNPH) and octanoate (PNPO), were examined. CD dimeis showed middling rate enhancements around neutrality. Catalytic rate constants ( kc) in the presence of 3a or 3b did not vary much with chain length of esters. In contrast, dissociation constants ( Kd) and selectivity factors (kc/Kd) for 'long-chain' esters were much smaller and significantly larger than those for short-chain ones respectively, indicating CD dimers 3a and 3b have good dimensional recognition ability and substrate selectivity in the hydrolytic cleavage of p-nitrophenyl alkanoates . Their kinetic consequences are briefly interpreted.
Linear and supercoiled DNA were cleaved by HPLC purified seryl histidine dipeptide(SH). It was found that the DNA fragments produced by the reaction of SH and DNA could be ligated together by T 4 DNA ligase. This result implied that the SH was the first example of the ion free artificial DNA cleavage agent that could split DNA by hydrolysis mechanism.
