Cytochrome P-450 and hydroxylating activity of microsomal preparations from whole houseflies

Abstract

1. A new microsomal preparation, obtained from whole houseflies is described in terms of its cytochrome P-450 content and its hydroxylating activity. 2. Microsomes prepared from whole-fly brei, obtained with the aid of a mortar (a procedure that avoids the destruction of sarcosomes), contain 0.265nmol of cytochrome P-450 and hydroxylate naphthalene at a rate of 28.5nmol/mg of microsomal protein in 30min at 30 degrees C. This corresponds to 104nmol of naphthalene hydroxylated/nmol of cytochrome P-450. This is the highest rate ever reported for housefly and rat liver microsomal preparations. 3. Microsomal fractions prepared by procedures that do not retain the integrity of sarcosomes show the presence in the CO-difference spectrum of a 428nm peak. This cytochrome is associated with sarcosomal microsomes and it may be involved in the inhibition of insect microsomal mixed-function oxidases, although other factors cannot be discarded at present. 4. The inability to show cytochrome P-450 in microsomal fractions isolated from whole houseflies by other procedures may be at least partially due to a masking effect brought about by contamination with the sarcosomal cytochrome.

UDP-glucosyltransferase activity of housefly microsomal fraction

“…Non-sexed 5-day-old specimens of the Fc housefly (Musca domestica) strain (Morello et al, 1971) were used throughout. Phenobarbital was administered in the food (Capdevila et al, 1973) at 0.5 % concentration for 72h before death.…”

“…Microsomal fractions were prepared by the mortar procedure of Morello et al (1971) in O.1M-sOdium phosphate buffer, pH7.5, and used immediately after preparation. The supernatant remaining after centrifugation of the microsomal fraction at 105OOOg for 90min corresponds to the cytosolic fraction.…”

“…Housefly microsomal fraction has been shown to catalyse actively the NADPH-linked cytochrome P450 reactions which lead to the conversion of numerous xenobiotics into more polar compounds (Morello et al, 1971). Types of attack include aromatic hydroxylation, 0-and N-dealkylation and aliphatic hydroxylation.…”

Biological Aspects of Cytochrome P450 and Associated Hydroxylation Reactions

“…Microsomes from whole houseflies hydroxylate naphthalene at a rate of 950 U/kg protein or 3.47 U/jimol cytochrome P450 which is faster than that observed with rat liver microsomes [104]. The abdomens of adult houseflies (Musca domestica vicina) have been shown to contain cytochrome P450 with the content per abdomen in female houseflies (more than 24 h after emergence from the pupa) being considerably more than in males.…”

Ecdysone 20-mono-oxygenase in the desert locust, Schistocerca gregaria

“…The relatively high recoveries for succinate dehydrogenase and NADPH-cytochrome P-450 (c) reductase suggest that some form of latency is occurring, whereby separation of subcellular fractions increases the activity of the enzymes relative to that present in the homogenate. The presence of NADPH-cytochrome P-450 (c) reductase in the cell sap fraction (S) is probably indicative of insufficient centrifugal force to sediment the entire 'microsomal' membrane population (Morello et al, 1971).…”