Kinetics and regulation of urea uptake in anabaena doliolum and anacystis nidulans

Abstract

The apparent Kmand Vmax values for urea uptake in Anabaena doliolum Bharadwaja were 250 μM and 568 nmol of urea (mg protein)-1 hr-1. In comparison, Anacystis nidulans IU 625 showed lower affinity, Kmbeing 400μM and Vmax 500 nmol of urea (mg protein)-1 hr-1. Urea uptake was optimal at pH 7.5, 15 Wm-2 illumination and 30°C. Maximum uptake was evident during the exponential growth phase. Cells pregrown on N2, urea or nitrate transported urea equally well, but there was essentially no uptake of urea in cells preincubated with ammonia for more than 24 hr. Nevertheless, ammonia did not inhibit urea uptake by urea grown cells. But the uptake of ammonia was reduced in the presence of urea. N-deficiency invariably stimulated uptake of urea. Experiments under different metabolic conditions revealed that uptake is an active process driven mainly by cyclic photophosphorylation. © 1987, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.