ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS Vol. 264, No. 1, July, pp. 28%294,198s Regulation of Ornithine Decarboxylase from Mycobacterium smegmatis DAVID BALASUNDARAM* AND ANIL K. TYAGIT’ *Department of Biochemistry, %t%bhbhai Pat& Cheat Institute, University of Delhi, Delhi 110 ME”, India, and ~Departmmt of Biochemistry, University of Delhi South Campus, Be&to Junrez Road, New Delhi 110 021, India Received June 181987, and in revised form March 2,1988 The activity of ornithine decarboxylase in Myo&xteriurn smegmatis is regulated by a novel macromolecular inhibitor-a ribonucleic acid. Addition of polyamines to the growth medium enhances the level of this inhibitor, suggesting that the level of this negative modulator changes in response to the intracellular concentration of poly- amines. Thus, while other modes of regulation may be operational, the control by polyamines at the transcriptional level leading to the generation of a specific RNA inhibitor seems to be a key element in the regulation of ornithine decarboxylase in mycobacteria. Q 1988 Academic Press, Inc. Mycobacteria are gram-positive, acid fast, aerobic bacteria comprising both pathogenic and nonpathogenic strains. Two of the pathogenic strains namely, Mg- &actor&m tuberculosis and M. lepraxz, are causative agents for tuberculosis and lep- rosy, respectively. Polyamines play an important role in various crucial cellular processes, cell growth, and differentiation (l-3) which is why their biosynthesis is gaining wide- spread importance as a logical target for metabolic and pharmacological interven- tion (4, 5). To date, there exists no study on the bio- synthesis of polyamines in mycobacteria and their involvement during various phases of mycobacterial growth. Putres- tine was even reported to be absent in M. smegmatis and M. phlei (6). However, Paulin et al. (5) have recently suggested that it may be possible to find specific drugs for mycobacterial diseases such as tuberculosis using inhibitors of polyamine biosynthetic enzymes. This study focuses i To whom correspondence should be addressed. specifically on the activity and regulation of ornithine decarboxylase (EC 4.1.1.1’7), the first and rate-controlling enzyme of the polyamine biosynthetic pathway. Or- nithine decarboxylase activity in various systems has been found to be regulated at both the translational and post-transla- tional levels (for references see (7, 8)). In addition, “Antizymes” are known to play an important role in its regulation (9-11). In this paper, we report that the activity profile of ornithine decarboxylase in M. smegmdis is concomitant with its growth rate and present evidence for the first time in support of a regulatory mecha- nism operational in mycobacteria wherein the activity of ornithine decarboxylase is regulated by a specific RNA inhibitor. MATERIALS AND METHODS DL-[l-“CjOrnithine, 47.2 mCi/mmol, was obtained from New England Nuclear; DL-[l-‘4C]arginine, 46.0 mCi/mmol, was procured from CEA (Gif-sur-Yvette, France). Microbial protease inhibitors (pepstatin, chymostatin, antipain, and leupeptin) as well as phenylmethylsulfonyl fluoride (PMSF)s and bovine s Abbreviations used: PMSF, phenylmethyl- sulfonyl fluoride; ODC, ornithine decarboxylase. 6lW3-9861188 $3.66 Copyright 0 1999 by Academic Press, Inc. All rights of reproduction in any form reserved. 288