| Study on insect antibacterial peptides has been made great progress in recent years. The insects used in the investigations belong to Holometabola including Lepidoptera and Diptera. The present paper deals with Periplaneta americana L., a hemimetalolous insect, as study material at the first time. .Induction, isolation, purify, antibacterial activity and biochemistry of antibacterial peptides of Periplaneta americana L. were studied.Antibacterial activity of hemolymph induced by E. coli, deltamethrin, insect physiology salt solution, ultraviolet ray and ultrasonic wave were conducted. The results show activity induced by Escherichia coli was the best. Deltamethrin was the second. The important thing is that deltamethrin can be used conveniently.Antibacterial activity of hemolymph of P. americana L. induced by Escerichia coli strain k88 was effected by its sex, developmental stage and age. Survival rate of young nymphs after being induced was minimum, and their antibacterial activity in hemolymph wasn't found. Survival rate of induced mature nymphs (120 hours) was 38%.. Survival rate of the adults younger than 10 days was lower than that of the adults older than 30 days. Survival rate of females in 10 days was higher than males but survival rate of females older than 30 days was low. Rate of P. americana L with antibacterial activity in hemolymph was also different in developmental stages. The antibacterial activity of adults hemolymph was found in 24 hours after they were treated with the a ratio of 24.4% of individuals of P. americana L with antibacterial activity in hemolymph in adults older than 30 days, and 71.4% in adults younger than 10 days. The antibacterial activity of hemolymph was the strongest from the period of 72 to 96 hours after P. americana L. were treated. At this period the rate of number of P. americana L. with antibacterial activity in hemolymph was 85.7% in adults younger than 10 days, and 77.8% in adults older than 30 days. In all treatments, rate of male adults with antibacterial activity in hemolymph was higher than females, The activity duration of males and females was 8 days and 7 days Respectively.106-108germ/ul of consistency of bacterial solution was the optimum quantityto injected into body of P. americana L. . Capacity of hemolymph extracted from induced insects should be less than 10ul.Antibacterial peptide was obtained by gel chromatography and ion exchange chromatography. Its amino sequence was KRFVQAGMIE...NSAVVPLGEA-NH2, molecular weight of the peptide is about 20x103u and isoeletric points is 8.2. The antibacterial peptide have a broad antibacterial spectrum, being highly effective against Escherichia coli; K88. K99. 1B, 2B, 3B, Staphyloccus aureus, Serratia marsescens, Bacillus anthracis. but not against fungus. Antibacterial peptide have better stability in high temperature. Antibacterial activity can be kept in pH5-9.Content of protein in hemolymph changed in 24 hours after P. americana L was treated, declining from 332.67mg/ml to 2121.34mg/ml, at the lowest level, then rised slowly, and recovered to the normal level in 120 hours.Content of amino was the least when P. americana L was inducted for 72 hours But antibacterial activity in hemolymph was maximum. The activity usually can be last for 7 days. 144 hours after treated, content of amino was recovered and antibacterial activity in hemolymph could not be found. Fatty is a factory for producting protein. Fatty increased after P. americana L was inducted for 24 hours, and declined in 72 hours. Antibacterial activity was not found in fatty.The results by electrophoresis show that no new material and antibacterial activity were found in grind liquid from head, bosom and feet but content of certain material in grind liquid from head increases obviously. The experiment shows that antibacterial substance was mainly in hemolymph.The photos taken by electronic microscope show that the antibacterial peptide acts on the cell-wall of bacteria, making the cell-wall hollow and internal matter leaked a...
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