Trehalose synthesis

J. Defaye, H. Driguez, B. Henrissat, I. Gelas, and E. Bar-Guilloux, Asymmetric acetalation of a-a-trehalose synthesis of a-D-galactopyranosyl and 6-deoxy-6-fluoro-ot-D-glucopyranosyl-a-D-glucopyranoside, Carbohydr. Res. 63 41 (1978). 

Evidence for the presence of hyperglycemic factors in the CC were reported first in P. americana (1) and supported subsequently in B. discoidalis (3). The HGHs act on the fat body, the synthetic source for trehalose in insects (22), to elevate phosphorylase activity and the conversion of glycogen stores to the precursors for trehalose synthesis (2,3). Initially, it was believed that HGHs activated phosphorylase via the synthesis of adenosine 3 5 -cyclic monophosphate (cAMP) in the same manner that glucagon or epinephrine activate liver phosphorylase in vertebrate animals (23). Injections of intact adult P. americana with synthetic Pea-CAH-I and -II result in a 50% net increase in fat body cAMP over water-injected controls accompanied by a more than 3-fold increase in fat body phosphorylase activity (24). However, the CAHs fail to elevate cAMP levels of fat bodies from P. americana in vitro even though both phosphorylase activity and trehalose synthesis increase (25). In the latter case, Ca + is essential for the action of the CAHs, and its omission from the incubation medium inhibits the hypertrehalosemic response. 

Bld-HrTH administration to B. discoidalis in vivo or to isolated fat body fails to stimulate either fat body cAMP levels or adenylate cyclase activity and supports the previous findings (25). Nevertheless, for B. discoidalis, fat body phosphorylase activity is elevated and trehalose levels increase both in vivo and in vitro, and calcium is essential in vitro in addition to Bld-HrTH. No stimulation of trehalose synthesis is noted with agents that elevate adenylate cyclase, such as forskolin, or by inhibitors of phosphodiesterase such as theophylline or isobutylmethylxanthine (IBMX). Additions of cAMP, dibutyryl cAMP or 8-bromo-cAMP are not stimulatory to trehalose synthesis either in vivo or in vitro. This same result was observed for P. americana in that neither cAMP nor dbcAMP stimulated trehalose production by fat body in vitro, and xanthine inhibitors of phosphodiesterase that should cause accumulation of intracellular cAMP were inhibitory, except for isobutylmethylxanthine (IBMX) which was stimulatory for unknown reasons (26). We have not observed a stimulatory effect by IBMX with B. discoidalis fat body in vitro. 

The exact mechanism by which the AKH/RPCHs activate fat body phosphorylase and trehalose synthesis remains uncertain. In P. americana, CC extracts with hypertrehalosemic activity neither stimulate trehalose-6-P synthase for trehalose synthesis nor increase fat body trehalose permeability (28). In all insect species tested, phosphorylase activation and glycogen degradation occur in response to CC extracts or AKH GH peptides (2.3.29-32). Therefore, all the data suggest... 

Ca + is required for phosphorylase activation in fat bodies of both P, americana (25) and discoidalis (personal observation). Addition of Ca + elevates fat body phosphorylase kinase activity in P. americana (33). and calmodulin inhibitors suppress CC-stimulated trehalose production by the fat body in vitro. However, direct addition of calmodulin to fat body phosphorylase kinase also suppresses the kinase activity. It is proposed that Ca + interacts directly with a calmodulin-like subunit of phosphorylase kinase to activate the enzyme, and the presence of exogenous calmodulin competes with the enzymic subunit for available Ca + (33). These results suggest that the HGHs may influence adipocyte Ca + levels related to phosphorylase activation to promote glycogenolysis for trehalose synthesis. Possibly, HGH-mediated fat body Ca levels may interact with polyphosphoinositides, diacyl glycerol and protein kinase C as second messengers for endocrine message transduction and phosphorylase activation. 

Values are mean SEM. For cytoheme ab synthesis, animals are decapitated on day 0 and injected with the designated dose of Bld-HrTH daily on days 2,3 and 4 and cytoheme ab synthesis measured on day 4 (60, ). For trehalose synthesis, animals are decapitated on day 5 and the designated dose of Bld-HrTH injected on day 6 at time zero and the hemolymph carbohydrate measured 2 hr later. 

Values are mean+SEM for the number of individual animals shown in parenthesis. Similar small letters indicate no significant differences between means (P 0.05) based on ANOVA and Fisher s PLSD test of individual means. Animals were decapitated on day 0 and injected with either Ringer, 100 pmoles of Bld-HiTH, 1.8 ig a-amanitin or both Bld-HrTH and amanitin on days 1, 2, 3 and 4 followed by determination of cytoheme ab synthesis on day 4 (W, 61). For trehalose synthesis capacity, animals were decapitated on day 0 and treated with either Ringer or 1.8 ig of a-amanitin on days 1, 2, 3 and 4 and the Bld-HrTH response determined on day 5 by injection of 20 pmoles of Bld-HrTH followed by measurement of hemolymph carbohydrate levels 2 hr later. 

Kandror, O., DeLeon, A., and Goldberg, A.L., Trehalose synthesis is induced upon exposure of Escherichia coli to cold and is essential for viability at low temperatures., Proc. Natl Acad. Sci USA, 99, 9727, 2002. 

Lee Y, Keeley LL. Intracellular transduction of trehalose synthesis by h3fpertrehalosemic hormone in the fat body of the tropical cockroach Blaberus discoidalis. Insect Biochem Mol Biol 1994 24 473 80. 

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