Phase diagrams of La1−xCaxMnO3\rm La_{1-x}Ca_xMnO_3 in Double Exchange Model with added antiferromagnetic and Jahn-Teller interaction

The phase diagram of the multivalent manganites $\rm La_{1-x}Ca_xMnO_3$, in space of temperature and doping $x$, is a challenge for the theoretical physics. It is an important test for the model used to study these compounds and the method of calculation. To obtain theoretically this diagram for $x<0.5$, we consider the two-band Double Exchange Model for manganites with added Jahn-Teller coupling and antiferromagnetic Heisenberg term. In order to calculate Curie and N\'{e}el temperatures we derive an effective Heisenberg model for a vector which describes the local orientation of the total magnetization of the system. The exchange constants of this model are different for different space directions and depend on the density of $e_g$ electrons, antiferromagnetic constants and the Jahn-Teller energy. To reproduce the well known phase transitions from A-type antiferromagnetism to ferromagnetism at low $x$ and C-type antiferromagnetism to G-type antiferromagnetism at large $x$, we argue that the antiferromagnetic exchange constants should depend on the lattice direction. We show that ferromagnetic to A-type antiferromagnetic transition results from the Jahn-Teller distortion. Accounting adequately for the magnon-magnon interaction, Curie and N\'{e}el temperatures are calculated. The results are in very good agreement with the experiment and provide values for the model parameters, which best describe the behavior of the critical temperature for $x<0.5$.Comment: 13 pages, 5 figure

The site of cyclic AMP-dependent protein kinase catalyzed phosphorylation of cytochrome P-450 LM2

AbstractThe phenobarbital-inducible form of cytochrome P-450 purified from rabbit liver microsomes is phosphorylated by cAMP-dependent protein kinase at a single site, the serine residue in position 128 of the amino acid sequence. The serine is located in a characteristic recognition sequence for cAMP-dependent protein kinase and is part of a primary structure which is conserved during evolution, present also in phenobarbitalinducible rat cytochrome and cytochrome P-450 CAM from Pseudomonas putida. The contribution of these findings to our understanding of the structure and membrane topology of cytochrome P-450 LM2 and its turnover regulated by phosphorylation is discussed