*Institute of Microbiology, Russian Academy of Sciences, pr. 60-1etiya Oktyabrya 7, k. 2, Moscow, 117811 Russia **Kazan State University, ul. Kremlevskaya 18, Kazan, 420008 Russia ***Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow, 117813 Russia ****Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 117071 Russia Received June 29, 1999 Abstraet--Alkyl-substituted hydroxybenzenes (AHBs), which are autoinducers of microbial dormancy (dl factors), were found to stabilize the structure of protein macromolecules and modify the catalytic activity of enzymes. In vitro experiments showed that C6-AHB at concentrations from 10 -4 to 10 -2 M, at which it occurs in the medium as a true solution and a micellar colloid, respectively, nonspecifically inhibited the activity of chymotrypsin, RNase, invertase, and glucose oxidase. C6-AHB-induced conformational alterations in protein macromolecules were due to the formation of complexes, as evidenced by differences in the fluorescence spec- tra of individual RNase and C6-AHB and their mixtures and in the surface tension isotherms of C6-AHB and trypsin solutions. Data on the involvement of dormancy autoinducers in the posttranslational modification of enzymes and their inhibition will provide further insight into the mechanisms of development and maintenance of dormant microbial forms. Key words: dormancy, dormancy autoinducers, d I factors, alkyl-substituted hydroxybenzenes, metabolism blockade, structural modification of enzymes There is increasing current interest in the mecha- nisms of microbial dormancy, a resting state character- ized by the reversible inactivation of cellular metabo- lism associated with an increase in cell resistance to environmental stresses. The knowledge of the molecu- lar mechanisms of dormancy can provide further insight into the general principles of regulation of cell metabolism and cytodifferentiation and into the strat- egy of microbial survival and adaptation to varying environmental conditions. Investigations of resting microbial forms (bacillar endospores, bacterial cysts, and fungal spores) have led to the following three independent hypotheses explain- ing the development and maintenance of the dormant state in microorganisms: (1) production of metabolic autoinhibitors (e.g., spore germination inhibitors), whose release from spores results in the cessation of the dormant state [1]; (2) dehydration of the spore protoplast due to changes in the ultrastructure of cells, the phase state of membranes, and their selective permeability [2, 3]; ~E-mail for correspondence: andlm@mail.ru (3) reversible inactivation of enzymes due to the for- mation of thermostable complexes with dipicolinate calcium [4]. It should be noted that there is some controversy between experimental data and the above hypotheses, probably accounted for by the great diversity of the structural, chemical, and biochemical properties of resting microbial forms. At the same time, the general properties of resting forms suggest that the mechanisms of their formation must be similar. From this point of view, of much interest is the role of low-molecular- weight regulatory substances involved in the formation and maintenance of metabolically dormant microbial forms. Earlier, we described alkyl-substituted hydroxyben- zenes (AHBs) as autoregulatory dl factors inducing the conversion of vegetative microbial cells to dormant cystlike refractory forms [5-10]. Factors dl modify the structure of membranes by increasing the microviscos- ity of the lipid stroma due to hydrogen bonding between the hydroxyl groups of the aromatic ring of the factors and membrane lipids. As a result, d~ factors enhance the permeability of membranes to monovalent ions, induce the dehydration of the cell protoplast, affect the activity of membrane-associated enzymes, 0026-2617/00/6902-0174525.00 9 2000 MAIK "Nauka/lnterperiodica"