Search PubMed⌕ Search

Biomedical subjects

P F Hall

Publications and source records attributed to P F Hall.

At least 163 records · Page 9Linked to original sources
PubMed1975

The role of mitochondrial cytochrome P-450 from bovine adrenal cortex in side chain cleavage of 20S,22R-dihydroxycholesterol.

The role of cytochrome P-450 in the side chain cleavage of 20S,22R-dihydroxycholesterol was investigated by examining the effect of carbon monoxide on the conversion of this substance to pregnenolone by cytochrome P-450 from bovine adrenocortical mitochondria; the effect of carbon monoxide on the conversion of cholesterol to pregnenolone by the same enzyme also was examined. Fifty per cent inhibition of side chain cleavage was produced by gas mixtures with the following ratios: CO:O2,1.5 for cholesterol and 1.2 for 20S, 22R-dihydroxycholesterol. Photochemical action spectra revealed that light of wavelength 451 nm decreased the inhibition of side chain cleavage of both substrates to a greater extent than light of other wavelenghts. It is concluded that the heme moiety of P-450 is involved in the cleavage of 20S,22R-dihydroxycholesterol.

Adrenal Cortex↗
PubMed1974

The stoichiometry of the conversion of cholesterol and hydroxycholesterols to pregnenolone (3beta-hydroxypregn-5-en-20-one) catalysed by adrenal cytochrome P-450.

The stoichiometry of the side-chain cleavage of cholesterol (cholest-5-en-3beta-ol), 20alpha-hydroxycholesterol (cholest-5-ene-3beta,20alpha-diol), and 20alpha,22-dihydroxycholesterol (cholest-5-ene-3beta,20alpha,22-triol) has been examined with respect to TPNH, oxygen and H(+). Side-chain cleavage of cholesterol can be described by the following equation:Cholesterol + 3TPNH + 3H(+) + 3O(2) --> Pregnenolone (3beta-hydroxypregn-5-ene-20-one) + isocapraldehyde + 3 TPN(+) 4H(2)OStoichiometry of 20 alpha-hydroxycholesterol is 2TPNH and 2O(2) per mole of cleavage and with 20alpha, 22-dihydroxycholesterol the values are 1:1:1. In addition 1 mole of H(+) is consumed per mole of TPNH oxidized in each of these reactions. These observations are in keeping with a mechanism previously proposed in the literature, namely:Cholesterol --> 20alpha-OH-Cholesterol --> 20alpha, 22-di-OH-Cholesterol --> pregnenoloneDiscordant observations are reviewed and it is concluded that insufficient data are available to sustain objections to this pathway.

Adrenal Glands↗