Radiolabeled Compounds Facilitate Pathway Analysis

Before radioactively labeled substrates became available, detection of intermediates and products was often quite dif- 

Comparison of the relative amounts of pathway intermediates and final products in normal and mutant organisms containing a defective enzyme in the pathway. The precursor, intermediates, and final product of the pathway are labeled A, B-D, and E, respectively. The enzymes 1, 2, 3, and 4 are indicated by the numbers over the reaction arrows. A cross through the reaction arrow indicates a defective enzyme. In the wild-type organism with no defective enzymes (top), 

Pathways Are Usually Studied Both in Vitro and in Vivo 

Metabolic chemistry is characterized by functionality. Each reaction is important because of its participation in a sequence of reactions, and each sequence interacts functionally with other sequences. 

Sequences may be broadly classified into two main types biosynthetic (anabolic) and degradative (catabolic). Anabolic sequences usually require energy, and catabolic sequences usually produce energy. 

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