Teichoic acids enzyme activity

Poly(ribitol phosphate) synthetase has been found in particulate fractions from Staphylococcus aureus H, and Lactobacillus plantatrum.lt ll-m The bulk of the activity in Lactobacillus plantarum was in crude, cell-wall preparations, and the enzyme is apparently located in the membrane, although intimate association with the wall itself has been suggested. Unlike the natural teichoic acid, the enzymically synthesized ribitol phosphate polymer was readily extracted with phenol hydrolysis by acid and by alkali gave the expected products, and oxidation with periodate indicated a chain length of 5-9 units, a value which compares well with that of 8 units for the natural polymer in the walls of this organism. 

Synthetic ribitol phosphate polymer, unlike teichoic acid in a wall, is readily extracted from the particulate enzyme or membrane preparation by treatment with phenol.18 Similarly, teichoic acid synthesized by intact cells in the presence of penicillin is only loosely attached to the wall,111 and it may be significant that, in each case, synthesis of teichoic acid has occurred without the simultaneous synthesis of glycosaminopeptide. It is now known that, in the normal wall, teichoic acid and glycosaminopeptide are attached to each other, and it has been suggested that the low activity of cell-free synthetase is due to the absence of suitable acceptor molecules of glycosaminopeptide. This possibility could account for the ease of removal of teichoic acid formed when simultaneous synthesis of glycosaminopeptide was not possible. 

The incorporation of the D-alanine ester groups is, presumably, the last stage in the biosynthesis of teichoic acids. Several organisms possess enzymes which activate D-alanine, that is, which form a D-alanyl-adenosine 5-phosphate-enzyme complex but, so far, there has been no demonstration of incorporation, in cell-free systems, of D-alanine into teichoic acid or any... 

The teichoic acids of the wall and membrane act as a buffer system maintaining a concentration of Mg2 in the range of 10-15 mM, which is the optimum value for the activity of enzymes associated with membranes 31). Changes of the Mg2 + concentration in the medium have no effect on the activity of membrane-bound enzymes if the system keeps both the membrane and the cell wall closely in contact. Preparations devoid of cell walls (lysozyme digestion) exhibit a dependence of enzyme activity on the Mg2 + concentration. The membrane fragments without LTAs show a marked influence of the Mg2+ concentration on enzyme activity 31). 

The insertion of D-alanine into teichoic acids is thought to occur after the polymer backbone has been constructed. An enzyme which is putatively involved in its activation , prior to addition, has been isolated from a strain of Lactobacillus easel It requires ATP and magnesium ions and appears to form an enzyme-bound amino-acyl-ATP complex. However, the addition of D-alanine in vivo occurs in a highly ordered environment and attempts to imitate it in vitro have not achieved rates of synthesis comparable with physiological levels. Very possibly the true acceptor in vivo is a lipoteichoic acid. 

The mechanisms outlined above provide explanations of the observed repeating structure and direction of growth of teichoic acids and related polymers. The enzyme activities needed and the intermediates involved can be demonstrated. They do not, however, provide any clue as to how the teichoic acid chains are initiated. 

The pattern of cleavage of the cell wall of B. subtilis by purified iV-acetyl-muramic acid L-alanine amidase has been studied in the absence, and in the presence, of a modifier protein that combines stoicheiometrically with the enzyme to stimulate its activity. The modifier protein did not affect the rate of the enzymic reaction, but changed the mode of cleavage of the cell wall from a random pattern to a sequential pattern. Binding of the enzyme to the cell wall and functional interaction with the modifier protein occurred only when the cell wall contained teichoic acids. It appears that cell-wall teichoic acids act as specific allosteric ligands for bacterial lytic enzymes. 

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