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The [Ca.sup.2} -dependent membrane interactions of a water soluble fragment of synaptotagmin I (C2AB), containing two C2 domains (C2A and C2B) was determined using site-directed spin labeling. The data showed that C2A and C2B are not independent in nature but influence their mutual membrane penetration, explaining occurrence of multiple C2 domains in proteins, which function in membrane trafficking and repair.

Ca(super 2+) regulation of erythrocyte AMP deaminase [isoform E (AMPD3)] was studied by examining in vitro effects of calmodulin (CaM) on the enzyme and by monitoring the influence of CaM antagonists on purine catabolic flow in freshly prepared erythrocytes under various conditions of energy imbalance. The results suggested a protein-protein interaction between Ca(super 2+) -CaM and isoform E.

A study is conducted to investigate the structural and functional significance of the five cysteine residues present in the Ca(super 2+) binding protein, Human calbindin D28k through a series of cysteine-to-serine mutations. The mutants are studied under relevant physiological redox potentials in which conformational changes are monitored using ANS binding.

The linker region and the C-terminus of cysteine string proteins (Csp) are interfering with exocytosis and could assign two functions to the C-terminus in Ca(super 2+)-simulated cells, that is the interaction with SNARE protein VAMP and modulation of Csp homodeimerization. Cross-linking in permeabilized clonal beta-cells revealed homodeimerization of Csp, which is stimulated by Ca(super 2+) and again modulated by the variant C-terminus.

Polarized Sr EXAFS on oriented Sr-reactivated samples show that Fourier peak II, which fits best to Mn at 3.5 A[ring] rather than lighter atoms, is dichroic, with a larger magnitude at 10 degree and a smaller magnitude at 80 degree. Ca (Sr) is proximal to the Mn cluster and lead to refined working models of the heteronuclear Mn4Ca cluster of the oxygen-evolving complex in PS II.

The role of adenosine 5-triphosphate (ATP) in the activation mechanism of alpha-ca(super 2+)/calmodulin-dependent protein kinase II(alpha CaMKII) was investigated using the T286A non-autophosphorytable mutant of alphaCaMKII. Electron micrographic images of negatively stained T286A-alphaCaMKII mutant protein had a similar appearance to those of dodecameric alphaCaMKII.

An investigation was carried out about the specificity and the affinity of the interaction of the N-terminal sequences of annexins A1 and A2 with [Ca.sup.2.plus]-S100A11. The findings revealed that the binding site for annexin A2 on S100A11 was similar to that observed for the annexin A1 but with distinct differences involving the C-terminus of the annexin A2 peptide.

The phosphoproteome of porcine heart mitochondria, as detected by the Pro-Q Diamond stain using two-dimensional (2-D) gel electrophoresis and (super 32)P radioisotopic analysis, is characterized and also an initial screen for mitochondrial kinases and phosphatases associated with these protein phosphorylations are performed. The results show the use of a phosphoproteome screen in determining mitochondrial signaling pathways and reveal new pathways for Ca(super 2+) modification of mitochondrial function at the level of MnSOD (manganese superoxide dismutase).

The activities of pyruvate dehydrogenase phosphatase isofrom 1 (PDP1) or just PDP1c are greatly increased by Ca2+-dependent binding to the L2 (inner lipoyl) domain of the dihydrolipoyl acetyltransferase (E2) core. Sedimentation and velocity and equilibrium studies revealed that PDP1c exists as a reversible monomer/dimer mixture with an equilibrium dissociation constant of 8.0 (plusmn) 2.5 muM and L2 binds tightly and preferentially to the PDP1c monomer.

The sensitivity of the effector enzyme can be determined by the affinity of the Ca(super 2+)-sensor protein and also by the relative affinities of its Ca(super 2+)-bound versus the Ca(super 2+)-free form for the effector enzyme. As a model we used Ca(super 2+)-sensitive activation of photoreceptor guanylyl cyclase (RetGC-1) by guanylyl cyclase activating proteins (GCAPs).

Fesselin may function as an actin-polymerizing factor that is regulated by Ca(super 2+) levels. The affinity of Ca(super 2+)-calmodulin to the fesselin-actin complex was approximately 10(super 8) M(super -1).

The role of the interaction of calcineurin homologous protein 1 (CHP1) with the Na(super +)/H(super +) exchanger 1 (NHE1) in EF-hand Ca(super 2+) binding motifs, in the intracellular pH dependent regulation of NHE1 is investigated. Results revealed that complex formation between CHP1 and the CHP1 binding domain of NHE1 cause marked increase in the Ca(super 2+) binding affinity by promoting a conformational change of the EF-hands towards the tightly Ca(super 2+)-binding affinity form, indicating presence of two Ca(super 2+) ions in CHP1 when associated with NHE1 cells.