PRESSURE AND TEMPERATURE-DEPENDENCE OF ENANTIOSELECTIVE EXCITED-STATEQUENCHING OF CHIRAL TB(III) AND EU(III) TRIS (PYRIDINE-2,6-DICARBOXYLATE) CHELATES BY VARIOUS C-TYPE FERRICYTOCHROMES

For mitochondrial ferricytochrome c from horse, cow and tuna and for b acterial cytochrome c-550 from Paracoccus versutus, the pressure and t emperature dependence of their quenching of racemic Tb(DPA)(3)(3-) and Eu(DPA)(3)(3-) (DPA = pyridine-2,6-dicarboxylate) luminescence in aqu eous solution is investigated. Of these energy transfer reactions the activation volumes (Delta V-#) and energies (E-a) are determined for t he ranges P = 0-3 kbar and T=15-40 degrees C. For the Lambda enantiome rs of Tb(DPA)(3)(3-) and Eu(DPA)(3)(3-), Delta V-# and E-a are almost the same for all proteins: 0.4 less than or equal to Delta V(#)less th an or equal to 1.1 cm(3)/mol and 0 less than or equal to E(a)less than or equal to 2 kJ/ mel. For the a enantiomer, whose luminescence is qu enched faster, the activation parameters vary significantly with the o rigin of the protein and they are different for Tb(DPA)(3)(3-) and Eu( DPA)(3)(3-). Values for Delta V-#,V-Delta range from +4.9+/-0.5 (Eu/ho rse) to + 0.5 +/- 0.5 cm(3)/mol (Tb/tuna); E-a ranges from +8 +/- 1 (T b/cow) to -1 +/- 1 kJ/mol (Tb/tuna). The degree of enantioselectivity in the quenching (E-q) by cytc from horse, cow, chicken and pigeon is almost the same and markedly higher than from tuna. The differing quen ching characteristics of the tuna protein are ascribed to the amino ac id variations near the exposed heme edge: Ile9 -->Thr, Thr28 --> Val a nd/or Phe46 --> Tyr. Other variations in this region, Thr47 --> Ser an d Ala15 --> Ser, do not affect E-q.