A culturc of I-wtobacillus sp. isolated from soil was found to contain glucose, xylose and ribose isomerase enzymes. Some of the factors affecting isomerase enzyme activities were studied with a view to isolate and purify the enzymes. Arsenate was not required in the enzyme reactions. At 10 mM Concentrations sodium arscnate showed 65 -70% inhibition of D-ghCOSe isomerase but did not affect D-xylose and D-ribose isomerases. At 5 mM concentrations EDTA showed 85-90% inhibition of D-glucose and D-ribose isomerases but not D-xylose isomerase. Caz+ ions showed inhibition of u-glucose isomerase a t a concentration of 1-2 mM, but inhibition could be reversed by increasing Mg2+ concentration in the enzyme reaction mixture. D-Glucose enzyme production was ma,ximal after 72 hrs of fermentation in shake flasks with YAMANAKA medium containing glucose and xylose, and glucose isomerase activity in the culture increased up to 5-6 generations.
Heat treatment of ultrasonic crude extract and of whole bacterial cells in the presence of Co2+/ Mgz+ ions gave insoluble fixed active D-glucose isomerase enzyme devoid of D-XyloSe and D-ribose isomerase activities. About 40 units (pM/min) of D-glucose isomerase activity per gram of dry cells were obtained in whole cell immobilization.
Sugar-isomerking enzymes are of importance in the conversion of sugar and studying the metabolism of sugars. Sugar-isomerizing activities have been reported in many organisms (POULSEN and ZITTAN 1976). According to YAMANAKA (1963) cells of heterolactic acid bacteria exhibit D-glUCOSe, D-xylose and D-ribose-isomerizing activities. Unlike P. hydrophila (MARYIIALL and K o o ~ 1957) D-glucose isomerase activity from heterolactic acid bacteria did not require arsenate for activity and required Mna+ ions. The present study deals with thc isomerases of Lactobacillus sp., an isolate from soil.
Methods
Microorganism: The Lactobacillus sp. isolate (BHATIA and PRABHU 1980) from soil was maintained on stabs of YAMANAKA'S agar medium ( Y A M ANAKA 1968) and subcultured biweekly.
Culture propagation: 50 ml ERLENMXYER flasks containing 20 ml of sterile YAMANAKA liquid medium were inoculated from an active stab and grown under rotary shaking condition (150 rpm) at 35 "C for 24-48 hrs and then transferred t o 100 ml of YAMANAKA medium in 250 ml ERLEN-MEYER fltisk. Cultivation was continued a t the above conditions for 72-96 hrs. Culturcs were then assayed for isomcrasc aclivities. This was considered t o be the first gcncration. Subsequent transfers of thc: culture at the above conditions were used t o increase the gcnerations of thc culture.