title: Properties of stearylamine liposomes containing tyrosine phenol-lyase.
abstract: The activity of tyrosine phenol-lyase, a chemotherapeutic enzyme with a dissociable pyridoxal phosphate cofactor, was studied after incorporation into multilamellar positively charged liposomes. Tyrosine phenol-lyase activity was assessed in the presence and absence of exogenous pyridoxal phosphate. A maximum of 75% total enzyme activity was associated with liposomes when prepared from a molar lipid ratio of egg lecithin, cholesterol, stearylamine (7 : 2 : 1, w/w). The total tyrosine phenol-lyase activity was comprised of 25% membrane-associated enzyme and 50% encapsulated enzyme. Encapsulation increased the stability of the enzyme under the in vitro conditions of cold storage at 4 degrees C for 3 weeks and under elevated temperatures up to 61 degrees C. Liposomal encapsulation afforded little protection against trypsin and no protection against whole mouse plasma in vitro. Heat-treated plasma (100 degrees C for 1 h) had little effect on the activity of free and encapsulated tyrosine phenol-lyase. These results indicated that whole plasma contained a heat-labile factor(s) which destroyed both the liposomal and free tyrosine phenol-lyase activity. Plasma clearance after intraperitoneal injection of tyrosine phenol-lyase in B6D2F1 female mice was retarded by liposomal encapsulation, particularly when the animals were pre-treated with empty liposomes; however, only a small proportion of free and liposomal tyrosine phenol-lyase was absorbed. The free enzyme rapidly lost holoenzyme activity after absorption but the liposomes maintained holoenzyme activity. Even though liposomes preserved holo-tyrosine phenol-lyase activity, the holoenzyme was not present in sufficient concentration to sustain a reduced plasma tyrosine level.
mesh_terms: D000588:Amines / Q000378:metabolism; D000818:Animals; D001769:Blood; D003080:Cold Temperature; D004355:Drug Stability; D004885:Erwinia / Q000201:enzymology; D005260:Female; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism*; D008190:Lyases / Q000378:metabolism*; D051379:Mice; D011732:Pyridoxal Phosphate / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology; D014447:Tyrosine Phenol-Lyase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000588:Amines; D008081:Liposomes; D011732:Pyridoxal Phosphate; D014357:Trypsin; D008190:Lyases; D014447:Tyrosine Phenol-Lyase; C009317:stearylamine