摘要:

AbstractDuring the last larval stage, corpora allata (CA) of Manduca sexta are inactivated by a factor from the brain. Apparently the same factor (allatinhibin, Al) is secreted by day 4 Vth instar brains kept overnight in Grace's medium. Al is rapidly inactivated by heat or acid but withstands exposure to alkali and can be recovered after freezing and lyophilization. Exposure to pronase, chymotrypsin, carboxypeptidases‐A and‐Y, as well as leucine aminopeptidase eliminated Al activity completely, whereas after exposure to trypsin and protease XVII‐S, some residual activity remained. Inactivation by pyroglutamate aminopeptidase is interprefed as being due to prolinase activity of this enzyme. Incubation of CA with gentamicin, an aminoglycoside antibiotic, affects neither their ability to produce JH in vitro nor their viability in implantation assays. However, Al did not inactivate CA in the presence of low concentrations of gentamicin. This effect was used to guard against false positive assay results possibly produced by allatotoxic contamination. Al was purified by chromatography on Sephadex G‐25. All activity recovered emerged from the columns in intermediate fractions with an apparent Mr of 1,000–2,000. © 1993 Wiley

ISSN:0739-4462    

DOI:10.1002/arch.940240402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe report on phospholipase A2(PLA2) activity in homogenates prepared from fat bodies of the tobacco hornwormManduca sexta.PLA2activity is responsible for hydrolyzing fatty acids from thesn‐2position of phospholipids. The rate of hydrolysis increased with increasing homogenate protein concentration up to ∼︁ 320 μg protein/ml reaction volume. Higher protein concentrations did not appreciably increase the rate of PLA2activity. As seen in some, but not all PLA2s from mammalian sources, hydrolyzing activity increased linearly with time. The fat body activity was sensitive to pH (optimal activity at pH 8–9) and temperature (optimal activity at ∼︁40°C). The activity was associated with fat body rather than hemolymph, because no activity was detected in cell‐free serum. The fat body PLA2activity differs from the majority of PLA2s with respect to calcium requirements. Whereas most PLA2s are calcium‐independent. A few others are known to require submicromolar calcium concentrations. The fat body activity appears to be calcium independent. These data show that a PLA2activity that can hydrolyze arachidonic acid from thesn‐2position of phospholipids is associated with the tobacco hornworm fat body. The biological significance of this activity relates to biosynthesis of eicosanoids. Pharmacological inhibition of PLA2impairs the ability of this insect to respond to bacterial infections. Since the impairment can be reversed by treatment with exogenous arachidonic acid, the PLA2activity may be an important step in eicosanoid biosynthesis. ©

ISSN:0739-4462    

DOI:10.1002/arch.940240403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe three major polyamines—putrescine, spermidine, and spermine—were studied and changes of their levels were examined in extracts of cerebral ganglia and fat body from adultAcheta domesticus.In nervous tissue, only spermidine and spermine were present and spermine was two‐ to three‐fold more abundant than spermidine. The polyamine levels were high up to day 3, decreased on day 4, and then remained relatively unchanged up to day 10. The spermidine/spermine ratios decreased during the imaginal life. Higher spermidine titres were observed in the neural tissue of egg‐laying females compared to virgin females. In the fat body, putrescine was detected together with spermidine and spermine. Spermidine and spermine levels were two‐fold higher than putrescine. Fat body of virgin females contained two times more polyamines than male fat body. Low at emergence, spermidine and spermine concentrations peaked on days 2–3 only in females, and egg‐laying was characterized by an increase of putrescine and spermidine titres. Starvation did not change polyamine contents, implying homeostatic regulation of the intracellular polyamine metabolism. These data showing tissue specific changes in polyamine levels during the imaginal life ofAcheta domesticuspoint to the physiological importance of polyamines as possible intracellular regulators during adult insect development. © 1993

ISSN:0739-4462    

DOI:10.1002/arch.940240404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe activities of ornithine decarboxylase and S‐adenosylmethionine decarboxylase, two key enzymes in polyamine metabolism, were determined during the first 10 days of imaginal life in the nervous tissue and the fat body of the adult cricketAcheta domesticus.The kinetic constants of the two enzymes were also determined in both tissues. Both decarboxylases presented a higher activity in fat body than in nervous tissue. In nervous tissue, the activity of the two enzymes peaked at 16 h postemergence, then slowly decreased up to day 3–4. By contrast, the enzymatic activities in fat body, low at emergence, strongly increased on day 2. Thereafter, whereas ornithine decarboxylase activity remained rather high. S‐adenosyl‐methionine decarboxylase activity dropped back to emergence levels by day 10. These results, examined in light of the temporal alterations of polyamine levels observed in the two tissues, demonstrate synchronous variations between polyamine contents and the enzymes involved in their biosynthesis. © 1993 Wiley

ISSN:0739-4462    

DOI:10.1002/arch.940240405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0739-4462    

DOI:10.1002/arch.940240401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY