The CAM Enzymes

There is increasing evidence that CAM is controlled to a great extent at the enzyme level. As outlined earlier (see Chap. 3), the main metabolic sequence linking malate to the reductive pentose cycle is  

those enzymes involving PEP carboxylation and regeneration, and malate production and degradation plus synthesis of the amino acids aspartate and alanine from the keto acids oxalacetate and pyruvate are deemed most interesting for our understanding in CAM. 

P-enolpyruvate carboxylase was first observed and measured in spinach leaf extracts by Bandurski and Greiner (1953), and was quickly shown to be an important carboxylating enzyme in succulent plants (e.g.. Walker, 1957). Since its discovery and implication in Crassulacean Acid Metabolism, it has been studied 

It can use Mg or Mn as activators. The plant enzyme can readily be separated from other metabolic proteins by techniques of ionic salting and ion exchange or electrophoretic chromatography (Ting and Osmond, 1973 a, b). 

Molecular weights of PEP-C from nonsucculent plants are reported to be about 350,000 (Maruyama et al., 1966 Smith, 1968 Ting and Osmond, 1973 a, b). Enama (1976) compared four species of C4 plants and found a value of 340,000 for 

---