■i*; 



43 

 PPO from most sources, as mentioned previously, have been reported 

 to be present in different molecular forms. The number of these forms 

 depends on the enzyme source and on methods used to prepare them. It has 

 been revealed that part of molecular forms are due to association- 

 dissociation phenomena which is attributed to (1) association of various 

 degrees of polymerization of similar units; (2) various combinations of 

 different subunits; (3) conformational changes of a single protein; or 

 combinations of these three possibilities (Vamos-Vigyazo, 1981). Much 

 attention has been paid to differences in the properties of multiple forms 

 of the enzyme and to the possible physiological significance of such 

 differences. These include differences in affinity and specificity to 

 phenolic substrates and to oxygen (Harel et al . , 1964; Kahn, 1976; Taneja 

 and Sachar, 1974), sensitivity to inhibitors (Constantinides and Bedford, 

 1967; Harel et al . , 1964), pH optima (Takeo and Uritani, 1965; Wong et 

 al., 1971), and inactivation by heat (Ben-Shalom et al., 1977; Fling et 

 al., 1963; Sussman, 1961). In addition, differences in isozyme patterns 

 were also reported in connection with subcellular organelles (Harel et 

 al., 1965), the stage of tissue development (Takeo and Baker, 1973; Taneja 

 et al., 1974), as result of attack by pathogens (Hyodo and Uritani, 1964), 

 or of treatment with plant hormones (Taneja and Sachar, 1977a, b). 



Enzyme Kinetics of lobster PPO 



Double-reciprocal plots for the oxidation of DL-DOPA and catechol by 

 both lobster PPOs are shown in Figures 8 and 9, respectively. Both 

 lobster PPOs were capable of catalyzing DL-DOPA and catechol. Australian 

 lobster PPO displayed a relatively greater Michael is constant (K = 3.57 



