Laccase(EC 1.10.3.2)is known to oxidize various aromatic and nonaromatic compounds via a radical-catalyzed reaction,which generally includes two types of laccase,Lac1 and Lac2.Lac1 oxidizes toxic compounds in the di...Laccase(EC 1.10.3.2)is known to oxidize various aromatic and nonaromatic compounds via a radical-catalyzed reaction,which generally includes two types of laccase,Lac1 and Lac2.Lac1 oxidizes toxic compounds in the diet,and Lac2 is known to play an important role in melanizing the insect exoskeleton.In this study,we cloned and sequenced the cDNA of the diamondback moth,Plutella xylostella Lac2(PxLac2),from the third instar larvae using polymerase chain reaction(PCR)and rapid amplification of cDNA ends techniques.The results showed that the full-length PxLac2 cDNA was 1 944 bp long and had an open reading frame of 1 794 bp.PxLac2 encoded a protein with 597 amino acids and had a molecular weight of 66.09 kDa.Moreover,we determined the expression levels of PxLac2 in different stages by quantitative PCR(qPCR).The results indicated that PxLac2 was expressed differently in different stages.We observed the highest expression level in pupae and the lowest expression level in fourth instar larvae.We also investigated the enzymatic properties of laccase,which had optimal activity at pH 3.0 and at 35°C.Under these optimal conditions,laccase had a Michaelis constant(Km)of 0.97 mmol L-1,maximal reaction speed(Vm)of 56.82 U mL-1,and activation energy(Ea)of 17.36 kJ mol-1 to oxidize2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid ammonium salt).Type II copper enhanced laccase activity below 0.8mmol L-1 and reduced enzyme activity above 0.8 mmol L-1 with an IC50 concentration of 1.26 mmol L-1.This study provides insights into the biological function of laccase.展开更多
Melanization/pigmentation is an important physiological phenomenon in insects,which is involved incuticular tanning,parasite encapsulation,and egg shell hardening.During the past few years,we have beenusing mosquito e...Melanization/pigmentation is an important physiological phenomenon in insects,which is involved incuticular tanning,parasite encapsulation,and egg shell hardening.During the past few years,we have beenusing mosquito eggs as a model to study the detailed biochemistry of melanization reactions in mosquitoes.Chorion of newly oviposited eggs is white and soft,but the chorion becomes black and hard within 3~4 hfollowing oviposition. Once the chorion turns black,the eggs become resistant to desiccation and solubiliza-tion.Floodwater mosquitoes,such as Aedes aegypti,oviposit on substrates at the edge of water and theeggs hatch only after being flooded with water following adequate rainfall.Consequently,the ability towithstand the desiccation and other environmental adversities is critical for egg survival.Our research deal-ing with chorion melanization in mosquitoes is aimed at understanding the biochemical processes and mech-展开更多
The anodic polarization curves of chromate zinc plates were studied under the condition of with and without illumination. It is found that the chromate film of zinc plate is characterized by an n type semi conductive ...The anodic polarization curves of chromate zinc plates were studied under the condition of with and without illumination. It is found that the chromate film of zinc plate is characterized by an n type semi conductive property. The illumination on the surface and the addition of Pb in the surface raises the anodic photocurrent and plays a part of the n type property in the film. Contrarily, Ag in the film plays a part of the p type dopant. The effects of quantitative Pb 2+ and Ag + in bath on the melanization(black patina) of zinc plate after chromate treatment also has been studied by comparing the lightness differences Δ L by means of a whiteness meter. It is found that the lightness decreasing process (the melanization rate) is consistent with the Wagner equation Δ L =kt 1/2 +C, and that Pb in the film increases k , on the other hand, Ag in the film decreases k of the melanizing rate.[展开更多
Melanization is harmful to the lightness of galvanized steel surface and also reduces the bonding force between a paint coat and the steel sheet. Experimental results showed that the hypothesis of Zn-Pb codeposition d...Melanization is harmful to the lightness of galvanized steel surface and also reduces the bonding force between a paint coat and the steel sheet. Experimental results showed that the hypothesis of Zn-Pb codeposition does not hold true, while the fact that PbSO4 micelles in sulfate bath settle on the coating surface support the second hypothesis. The authors come to the conclusions that (1) Any measure to eliminate PbSO4 micelles before or after passivation of the coating will prevent melanization; (2) PbSO4 micelles adsorbed on the surface of passivated film promote the growth of oxygen-deficient Zn oxide and result in the generation of melanization.展开更多
基金supported financially by the National Natural Science Foundation of China (31672046)the National Key Research and Development Program of China (2016YFD0200500)the Funds of Shandong "Double Tops" Program, China (SYL2017YSTD06)
文摘Laccase(EC 1.10.3.2)is known to oxidize various aromatic and nonaromatic compounds via a radical-catalyzed reaction,which generally includes two types of laccase,Lac1 and Lac2.Lac1 oxidizes toxic compounds in the diet,and Lac2 is known to play an important role in melanizing the insect exoskeleton.In this study,we cloned and sequenced the cDNA of the diamondback moth,Plutella xylostella Lac2(PxLac2),from the third instar larvae using polymerase chain reaction(PCR)and rapid amplification of cDNA ends techniques.The results showed that the full-length PxLac2 cDNA was 1 944 bp long and had an open reading frame of 1 794 bp.PxLac2 encoded a protein with 597 amino acids and had a molecular weight of 66.09 kDa.Moreover,we determined the expression levels of PxLac2 in different stages by quantitative PCR(qPCR).The results indicated that PxLac2 was expressed differently in different stages.We observed the highest expression level in pupae and the lowest expression level in fourth instar larvae.We also investigated the enzymatic properties of laccase,which had optimal activity at pH 3.0 and at 35°C.Under these optimal conditions,laccase had a Michaelis constant(Km)of 0.97 mmol L-1,maximal reaction speed(Vm)of 56.82 U mL-1,and activation energy(Ea)of 17.36 kJ mol-1 to oxidize2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid ammonium salt).Type II copper enhanced laccase activity below 0.8mmol L-1 and reduced enzyme activity above 0.8 mmol L-1 with an IC50 concentration of 1.26 mmol L-1.This study provides insights into the biological function of laccase.
文摘Melanization/pigmentation is an important physiological phenomenon in insects,which is involved incuticular tanning,parasite encapsulation,and egg shell hardening.During the past few years,we have beenusing mosquito eggs as a model to study the detailed biochemistry of melanization reactions in mosquitoes.Chorion of newly oviposited eggs is white and soft,but the chorion becomes black and hard within 3~4 hfollowing oviposition. Once the chorion turns black,the eggs become resistant to desiccation and solubiliza-tion.Floodwater mosquitoes,such as Aedes aegypti,oviposit on substrates at the edge of water and theeggs hatch only after being flooded with water following adequate rainfall.Consequently,the ability towithstand the desiccation and other environmental adversities is critical for egg survival.Our research deal-ing with chorion melanization in mosquitoes is aimed at understanding the biochemical processes and mech-
文摘The anodic polarization curves of chromate zinc plates were studied under the condition of with and without illumination. It is found that the chromate film of zinc plate is characterized by an n type semi conductive property. The illumination on the surface and the addition of Pb in the surface raises the anodic photocurrent and plays a part of the n type property in the film. Contrarily, Ag in the film plays a part of the p type dopant. The effects of quantitative Pb 2+ and Ag + in bath on the melanization(black patina) of zinc plate after chromate treatment also has been studied by comparing the lightness differences Δ L by means of a whiteness meter. It is found that the lightness decreasing process (the melanization rate) is consistent with the Wagner equation Δ L =kt 1/2 +C, and that Pb in the film increases k , on the other hand, Ag in the film decreases k of the melanizing rate.[
基金Tlle work was financially supported by ShanghaiBaoshan Steel Company.
文摘Melanization is harmful to the lightness of galvanized steel surface and also reduces the bonding force between a paint coat and the steel sheet. Experimental results showed that the hypothesis of Zn-Pb codeposition does not hold true, while the fact that PbSO4 micelles in sulfate bath settle on the coating surface support the second hypothesis. The authors come to the conclusions that (1) Any measure to eliminate PbSO4 micelles before or after passivation of the coating will prevent melanization; (2) PbSO4 micelles adsorbed on the surface of passivated film promote the growth of oxygen-deficient Zn oxide and result in the generation of melanization.