Abstract: To investigate whether chilling at 5℃ changes the metabolism of NAD in diapause eggs of the silkworm, Bombyx mori, the levels of NADH and NAD⁺ along with the activities of lactate dehydrogenase (LDH) and cytosolic malate dehydrogenase (cMDH) in diapause eggs incubated at 25℃ and 5℃, respectively, were determined using HPLC and spectrophotometric methods. NAD (NADH + NAD⁺) levels and the cMDH activity in diapause eggs incubated at 5℃ increased by 106% and 53%, respectively, which were significantly higher than those in diapause eggs incubated at 25℃ (P<0.01). However, no significant difference in the NADH/NAD⁺ ratio and the LDH activity was observed between the incubation treatments at 25℃ and 5℃ (P>0.05). It is so inferred that the ability for NAD⁺ synthesis and regeneration in Bombyx diapause eggs is enhanced by chilling.

Key words: Bombyx mori, diapause termination, nicotinamide adenine dinucleotide, lactate dehydrogenase, cytosolic malate dehydrogenase