TY - JOUR
T1 - Mechanistic and Metabolic Studies of Sterol 24,25-Double Bond Reduction in Manduca sexta
AU - Short, Janel D.
AU - Guo, De An
AU - Svoboda, James A.
AU - Nes, W. David
PY - 1996
Y1 - 1996
N2 - Larvae of Manduca sexta were used to obtain a cell-free sterol 24,25-reductase. From the midgut of fifth instar larvae fed a mixture of sitosterol and campesterol a microsome-bound 24,25-sterol reductase was prepared that transformed desmosterol (Km, 3 μM), lanosterol (Km, 18 μM), and cycloartenol (Km, 33 μM) to cholesterol, 24,25-dihydrolanosterol, and cycloartanol, respectively. With desmosterol as substrate, the microsome-bound enzyme was found to incorporate tritium into cholesterol from 4S-tritium labelled NADPH. [24-2H]lanosterol was transformed by larvae to [24-2H]24,25-dihydrolanosterol (structure confirmed by mass spectroscopy (MS) and 1H-nuclear magnetic resonance spectroscopy. A rationally designed inhibitor of 24,25-reductase activity, 24(R,S),25-epiminolanosterol (IL), was assayed and found to be inhibitory with an I50 of 2 μM. IL was supplemented in the diet of M. sexta with either sitosterol or stigmasterol and found to inhibit development (I50, 60 ppm). The major sterol which accumulated in the IL-treated larvae was desmosterol, confirming the site of inhibition was reduction of the 24,25-bond. IL was converted to [2-3H]IL when fed to the larvae. [2-3H]lanosterol was recovered from fifth instar larvae and its structure confirmed by MS and radiochemical techniques.
AB - Larvae of Manduca sexta were used to obtain a cell-free sterol 24,25-reductase. From the midgut of fifth instar larvae fed a mixture of sitosterol and campesterol a microsome-bound 24,25-sterol reductase was prepared that transformed desmosterol (Km, 3 μM), lanosterol (Km, 18 μM), and cycloartenol (Km, 33 μM) to cholesterol, 24,25-dihydrolanosterol, and cycloartanol, respectively. With desmosterol as substrate, the microsome-bound enzyme was found to incorporate tritium into cholesterol from 4S-tritium labelled NADPH. [24-2H]lanosterol was transformed by larvae to [24-2H]24,25-dihydrolanosterol (structure confirmed by mass spectroscopy (MS) and 1H-nuclear magnetic resonance spectroscopy. A rationally designed inhibitor of 24,25-reductase activity, 24(R,S),25-epiminolanosterol (IL), was assayed and found to be inhibitory with an I50 of 2 μM. IL was supplemented in the diet of M. sexta with either sitosterol or stigmasterol and found to inhibit development (I50, 60 ppm). The major sterol which accumulated in the IL-treated larvae was desmosterol, confirming the site of inhibition was reduction of the 24,25-bond. IL was converted to [2-3H]IL when fed to the larvae. [2-3H]lanosterol was recovered from fifth instar larvae and its structure confirmed by MS and radiochemical techniques.
KW - Cholesterol
KW - Desmosterol
KW - Manduca sexta
KW - Sitosterol
KW - Tobacco hornworm
UR - http://www.scopus.com/inward/record.url?scp=0008032125&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1520-6327(1996)31:1<1::AID-ARCH1>3.0.CO;2-4
DO - 10.1002/(SICI)1520-6327(1996)31:1<1::AID-ARCH1>3.0.CO;2-4
M3 - Article
AN - SCOPUS:0008032125
SN - 0739-4462
VL - 31
SP - 1
EP - 22
JO - Archives of Insect Biochemistry and Physiology
JF - Archives of Insect Biochemistry and Physiology
IS - 1
ER -