METABOLIC BLOCKS IN THE DEGRADATION OF BETA-SITOSTEROL BY A PLASMID-CURED STRAIN OF ARTHROBACTER-OXYDANS

Plasmid-harbouring, sterol-decomposing organism Arthrobacter oxydans 317 was treated with sodium dodecylsulphate to obtain a plasmid-cured strain A. oxydans 317 A1 incapable of utilizing 4-androstene-3, 17-dione (AD). The strain 317 A1 was unable to degrade beta-sitosterol side chain completely to form AD but could carry out partial degradation as shown by the accumulation of 3-oxochol-4-en-24-oic acid as a major metabolite and 27-norcholest-4-en-3,24-dione as a minor metabolite. The strain could form 1,4-androstadiene-3,17-dione (ADD) from 3-oxo-23,24-bisnorchol-1,4-dien-22-oic acid (BNC) to a limited extent. The existence of metabolic blocks in the conversion of 3-oxochol-4-en-24-oic acid to 3-oxo-23,24-bis-norchol-4-en-22-oic acid and further conversion to AD by the plasmid-cured strain 317 A1 was suggested. Neither the formation of ADD from AD nor the conversion of AD and ADD to 9-alpha-hydroxy derivatives leading to steroid ring opening could be done by the plasmid-cured strain but the 17-beta-reduction of AD and ADD and 1(2)-reduction of ADD were not affected by the absence of the plasmid. It was proposed that plasmid determines 1(2)-dehydrogenation and 9-alpha-hydroxylation of steroid ring structure in this organism.