Penicillin Inhibits the Transpeptidation Reaction

The inhibitory mechanism is shown in figure 16.20. First the transpeptidase (TPase) reacts with one strand of the substrate to form an acyl enzyme intermediate, thus eliminating D-alanine. This intermediate then reacts with another strand to form the cross-link and regenerate the enzyme. Because penicillin is an analog of alanylalanine, it fits 

In addition to penicillin several other antibiotics (phosphonomycin, bacitracin, and vancomycin) block cell wall synthesis at different locations (see figs. 16.16 and 16.17). In addition to their biological and medical importance, these antibiotics have been very useful in elucidating the biosynthetic pathway. This is because they cause accumulation of the intermediate before the blocked step. This species can frequently be isolated and confirmed as a genuine intermediate in the pathway. 

The third stage of cell wall synthesis. This diagram shows the cross-linking reaction and the mechanism of inhibition by penicillin in the bacterium Staphylococcus aureus. 

This chapter focuses on the synthesis of complex carbohydrates. It begins with a consideration of the hexoses that are the building blocks of complex carbohydrates. Then some aspects of the synthesis of simple homopolysaccharides are examined followed by a brief consideration of heteropolymers that contain more than one hex-ose. A major portion of the chapter is concerned with glycoproteins that contain complex linear and branched carbohydrates attached to proteins. Finally the synthesis of the bacterial wall is examined. 

Hexoses, which are the primary building blocks of oligosaccharides and polysaccharides, come in a large variety of types. All hexoses can be derived from glucose through a series of conversions. These conversions usually occur at the level of the monophosphor- 

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