Al. Leitao et al., ALLOPHANE INCREASES THE PROTEIN-LEVELS OF SEVERAL CEPHAMYCIN BIOSYNTHETIC-ENZYMES IN NOCARDIA LACTAMDURANS, Microbiology, 142, 1996, pp. 3399-3406
Addition of allophane, a phosphate-trapping agent, to two different st
rains of Nocardia lactamdurans exerted a large stimulatory effect on c
ephamycin biosynthesis. The biosynthesis of cephamycin is inhibited by
inorganic phosphate at concentrations above 5 mM and allophane revers
ed this inhibitory effect. Allophane-supplemented cultures showed incr
eased activities and/or an extended life in the cell of four cephamyci
n biosynthetic enzymes: isopenicillin N synthase, the two-protein-comp
onent 7 alpha-cephem methoxylase (7 alpha-cephem hydroxylase and 7-hyd
roxycephem methyltransferase) and 3'-hydroxymethylcephem 0-carbamoyltr
ansferase. However, the first enzyme of the pathway, lysine 6-aminotra
nsferase, was not stimulated by allophane. Allophane-supplemented cult
ures showed increased protein levels of (i) alpha-aminoadipyl-cysteiny
l-valine synthetase (the condensing multienzyme that forms the tripept
ide intermediate), and (ii) the two proteins involved in the 7 alpha-c
ephem methoxylase, as shown by immunoblotting with antibodies against
each of these proteins. Phosphate repressed the de novo synthesis of t
hese proteins but did not increase their degradation. These results in
dicated that allophane stimulates expression of the cluster of genes e
xtending from the pcbAB gene (encoding alpha-aminoadipyl-cysteinyl-val
ine synthetase) to cmcI-cmcJ (encoding the two-protein methoxylase) an
d cmcH (encoding the 0-carbamoyltransferase).