Energetics of pupal-adult metamorphosis in the silkworm, Bombyx mori : An analysis of transdeamination parameters in the fat body and haemolymph

Abstract

Transdeamination seems to be an important alternative energy-intensive gluconeogenesis mechanism that generates glucose from non-carbohydrate sources during pupal-adult metamorphosis in Bombyx mori. Studies on four transdeamination parameters, viz., free amino acids (FAA), aspartate aminotransferase (AAT), alanine aminotransferase (AlAT) and glutamate dehydrogenase (GDH) in the fat body and haemolymph of silkworm have indicated that transdeamination shows stage-specific, region-specific and sex-specific variations during metamorphosis. Region-specific growth trends indicate that the transamination reaction, mediated by AAT and AlAT is faster in the abdominal fat body (AFB) and relatively slower in the thoracic fat body (TFB) with concomitant lower FAA levels in the former and higher levels in the latter. Stage-specific growth trends reflect that the energy mobilization through transdeamination assumes greater significance in the early pupal, late pupal and adult stages rather than the mid-pupal stage. Sex-wise trends in FAA levels indicate that the rate of amino acid utilization is significantly faster in females compared to that in males. Further, the growth trends in the levels of GDH vis-à-vis aminotransferases signify that the energy demands of male sex expressions are met largely through enhanced levels of GDH and that the alpha ketoglutarate generated in transamination reaction is used as a substrate for sperm production, sperm motility and successful mating that stimulates fecundity and productivity of in the mulberry silkworm. The study clearly demonstrates that gluconeogenesis through transdeamination supplements the energy requirements of silkworm metamorphosis and that it is facilitated by disintegrating tissues predominantly from the pupal abdominal segments.