| The proteins were isolated by sulfate precipitation on different saturation ranges from six kinds of cactus, Mammillaria Haw. Notocactus A.Beraer,Opuntia Mill,Hylocereus Britt et Rose, et al, and their antimicrobial activities were tested to screen the cactus with antimicrobial peptides. The SephadexG-75 and Sephadex G-25 was used to further purify the peptide with most effective antimicrobial activity. SDS-PAGE,Proline and Ninhydrin Reaction,Resistance-Bacterial Test, et al were used to analysis its characterization. The main result were described as following:The proteins from four kinds of tested Cactus had antimicrobial activities and most of these isolated by sulfate precipitation on the saturation ranges from 40%～80%, partly exceeded 80%, that indicating the molecular weight of these proteins are low. Especially, the proteins extracted from Mammillaria Haw. were most effective on antimicrobial activity.Hot-treated Staphylococcus aureus were used to induce Mammillaria Haw by three different methods. The result showed that the inhibited zones surrounding the induced plant tissues were obviours compared with no induced tissues. And further reseach indicated that the inhibition rate was increased rapidly in 24 hours after induced by bacterium and the rate acheived maximum in 72 hours.An antimicrobial peptide named MH-AMP-1, witch molecular weight was about 8511 Da, was isolated and purified form Mammillaria Haw. During the process of purification, about 55% not target protein was removed while the content of MH-AMP-1 was purified 2.96 times than origin. The specific activity was improved to 376.81 U·mg-1 by SephadexG-75 and Sephadex G-25 gel filtration chromatography and about 5.52% MH-AMP-1 was recovered. An electrophoresis-grade antibacterial peptide was proved by Polyacrylamide gel electrophoresis(SDS-PAGE).The thermostable. research proved that the antimicrobial activity was not changed under 70℃environment while the antimicrobial activity decreased little on 80℃～90℃after 1 h. And MH-AMP-1 remained 80% antimicrobial activity on 100℃. These indicated that the MH-AMP-1 was thermostable to some extent. The result of pH influence test showed that MH-AMP-1 was also active on pH2.5～7.5 environment while its activity decreased obviously when the pH of environment was over pH8 which indicated that the MH-AMP-1 possessed positive charges.The test of acivity spectrum and MIC of MH-AMP-1 showed that: MH-AMP-1 was able to inhibite the growth of Bacillus cereus,Actinomyces pyogenes,Candida albicans,Cryptococcus neofornans and it can strongly inhibite the growth of Staphylococcus aureus,Salmonella derby,Bacillus subtilis,Bacillus megaterium,Pseudomonas pyocyanea.This indicated that MH-AMP-1 could kill most pathogens. And MIC value of MH-AMP-1 was 30μg·mL-1 towards S. aureus and B. subtilis, 60μg·mL-1 towards B. cereus and C. neofornans, while 120μg·mL-1 towards C. albicans.A novel antimicrobial peptide was obtained from Mammillaria Haw through screening, induction, isolation and purification. This indicates that the antimicrobial activity of cactus was result of antimicrobial peptide witch was encoded by DNA,in addition to chemical constituents, compared with the traditional concepts.
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