PROFLAVINE-SENSITIZED SELECTIVE PHOTOOXXDATION OF THE TRYPTOPHYL RESIDUES IN PAPAIN

Abstract— A detailed analysis of the effects of acidic pH values and of temperature on the ultraviolet absorption spectrum of papain demonstrated that the protein can exist in several more or less denatured conformations depending on the surrounding medium. Proflavine-sensitized photooxidation of papain, under experimental conditions corresponding to the spectroscopically detected conformational states, allowed us to modify separately the five tryptophyl residues. Tryptophan-7 and 69 appear to be at least partially exposed to the aqueous environment in native papain; however, the former becomes inaccessible to the photooxidizing agent at temperatures lower than 15°C. The photooxidative conversion of these residues to formyl-kynurenine has no appreciable effect on the tertiary structure as well as on the enzymic activity of papain. On the other hand, tryptophan-177. which appears to be largely buried, can also be modified with minor variations in the spatial geometry of the protein, but its indole moiety must be critically involved in the enzyme-substrate interaction, since its conversion to formyl-kynurenine almost completely inhibits the catalytic activity. Finally, tryptophan-181 and -26 are deeply buried in internal hydrophobic clusters and become available to photooxidation only after the protein molecule has been extensively disorganized. Our results suggest that the solution conformation of some areas of the papain molecule may be different from that in the crystal state as deduced from X-ray diffraction studies.     

A COMPARISON OF FLUORESCENCE METHODS USED IN THE PHARMACOKINETIC STUDIES OF Zn(II)PHTHALOCYANINE IN MICE

The pharmacokinetics of Zn phthalocyanine (ZnPc) encapsulated in dipalmitoyl-phosphatidylcholine (DPPC) liposomes, injected intravenously in Skh:HR-1 nude mice, was monitored by two in vitro techniques and one in vivo technique, all based on fluorescence spectroscopy. The in vitro methods involve either fluorescence measurements on thin tissue sections or on extracts from these tissues. The in vivo method involves the fluorescence measurement at the skin surface. Both in vitro techniques gave similar results which are consistent with previous findings on the pharmacokinetic behavior of ZnPc. The liver and spleen showed rapid ZnPc concentration increases, reaching a maximum level in 30 min. or less post drug administration. Relatively little ZnPc was detected in the skin, fat or muscle, the maximum concentration occurring at 12 h. In vivo fluorescence reached a maximum intensity approx. 6 h post injection at the mid-chest analysis site and at 12 h in the thigh. The in vivo measurements at two different anatomical sites showed pharmacokinetic behavior that reflects an overall integrated fluorescence originating from several tissue sites.     

Limit Design in the Absense of a Given Layout: A Finite Element,Zero-One Programming Approach∗

Limit design in three dimensions is discussed and formulated as a constrained minimax problem in kinematic and geometric variables. A finite element discretization is proposed which, combined with piecewise linearization of the yield surfaces, reduces the minimum weight design to a pair of dual problems in linear mixed zero one programming. The relevant duality theory is shown to be useful for the theoretical frame of the mechanical problem. Various ways of reducing the number of variables and constraints are pointed out, in order to make available algorithms economically applicable to practical situations.     

PROFLAVINE-SENSITIZED PHOTOOXIDATION OF METHIONINE

Abstract— A study was made of the kinetics of the proflavine-sensitized photooxidation of methionine to methionine sulfoxide. The reaction is inhibited by the paramagnetic ions Cu²⁺ and Mn²⁺, which suggests that the triplet state of the sensitizer is an intermediate. A mechanism is proposed in which methionine reacts with the first singlet state of oxygen, produced by energy transfer from the triplet sensitizer. The decrease in the rate of photooxidation with increasing proflavine concentration is ascribed to self-quenching of the excited singlet state of the dye.     

UNUSUALLY HIGH AFFINITY OF Zn(II)-TETRADIBENZOBARRELENOOCTABUTOXY- PHTHALOCYANINE FOR LOW-DENSITY LIPOPROTEINS IN A TUMOR-BEARING MOUSE

Abstract— An important factor in determining the efficacy of photosensitizing compounds in photodynamic therapy of tumors is the level to which tumors take up the photosensitizers after systemic injection. This parameter seems to be related to the transport modalities of the photosensitizer in the bloodstream. In this work the photosensitizer Zn(II)-tetradibenzobarreleno-octabutoxyphthalocyanine was shown to have an unprecedentedly high association with low-density lipoproteins (71% of the phthalocyanine in the plasma) when delivered in Cremophor micelles to tumor-bearing mice. This was accompanied by a particularly high tumor uptake at 24 h post-injection.