Measurements of air density determined gravimetrically and by using the CIPM-81/91 formula, an equation of state, have a relative deviation of 6.4 × 10 −5 .This difference is consistent with a new determination of the mole fraction of argon x Ar carried out in 2002 by the Korea Research Institute of Standards and Science (KRISS) and with recently published results from the LNE. The CIPM equation is based on the molar mass of dry air, which is dependent on the contents of the atmospheric gases, including the concentration of argon. We accept the new argon value as definitive and amend the CIPM-81/91 formula accordingly. The KRISS results also provide a test of certain assumptions concerning the mole fractions of oxygen and carbon dioxide in air. An updated value of the molar gas constant R is available and has been incorporated in the CIPM-2007 equation. In making these changes, we have also calculated the uncertainty of the CIPM-2007 equation itself in conformance with the Guide to the Expression of Uncertainty in Measurement, which was not the case for previous versions of this equation. The 96th CIPM meeting has accepted these changes.

The myristoylated alanine-rich protein kinase C substrate (MARCKS) is a major protein kinase C (PKC) substrate in many different cell types. MARCKS is bound to the plasma membrane, and several recent studies suggest that this binding requires both hydrophobic insertion of its myristate chain into the bilayer and electrostatic interaction of its cluster of basic residues with acidic lipids. Phosphorylation of MARCKS by PKC introduces negative charges into the basic cluster, reducing its electrostatic interaction with acidic lipids and producing translocation of MARCKS from membrane to cytoplasm. The present study shows that physiological concentrations of MARCKS (<10 microM) inhibit phospholipase C (PLC)-catalyzed hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) in phospholipid vesicles. A peptide corresponding to the basic cluster, MARCKS(151-175), produces a similar inhibition, which was observed with both PLC-delta1 and -beta1. Direct fluorescence microscopy observations demonstrate that the MARCKS peptide forms lateral domains enriched in the acidic lipids phosphatidylserine and PIP2 but not PLC, which accounts for the observed inhibition of PIP2 hydrolysis. Phosphorylation of MARCKS(151-175) by PKC releases the inhibition and allows PLC to produce a burst of inositol 1,4, 5-trisphosphate and diacylglycerol.

Direct fluorescence digital imaging microscopy observations demonstrate that a basic peptide corresponding to the effector region of the myristoylated alanine-rich C kinase substrate (MARCKS) self-assembles into membrane domains enriched in the acidic phospholipids phosphatidylserine (PS) and phosphatidylinositol 4,5-bisphosphate (PIP2). We show here that pentalysine, which corresponds to the first five residues of the MARCKS effector region peptide and binds to membranes through electrostatic interactions, also forms domains enriched in PS and PIP2. We present a simple model of domain formation that represents the decrease in the free energy of the system as the sum of two contributions: the free energy of mixing of neutral and acidic lipids and the electrostatic free energy. The first contribution is always positive and opposes domain formation, whereas the second contribution may become negative and, at low ionic strength, overcome the first contribution. Our model, based on Gouy-Chapman-Stern theory, makes four predictions: 1) multivalent basic ligands, for which the membrane binding is a steep function of the mole fraction of acidic lipid, form domains enriched in acidic lipids; domains break up at high concentrations of either 2) basic ligand or 3) monovalent salt; and 4) if multivalent anionic lipids (e.g., PIP2) are present in trace concentrations in the membrane, they partition strongly into the domains. These predictions agree qualitatively with experimental data obtained with pentalysine and spermine, another basic ligand.

The structure of E. coli adenylate kinase with bound AMP and AMPPNP at 2.0 A resolution is presented. The protein crystallizes in space group C2 with two molecules in the asymmetric unit, and has been refined to an R factor of 20.1% and an Rfree of 31.6%. In the present structure, the protein is in the closed (globular) form with the large flexible lid domain covering the AMPPNP molecule. Within the protein, AMP and AMPPNP, and ATP analog, occupy the AMP and ATP sites respectively, which had been suggested by the most recent crystal structure of E. coli adenylate kinase with Ap5A bound (Müller and Schulz, 1992, ref. 1) and prior fluorescence studies (Liang et al., 1991, ref. 2). The binding of substrates and the positions of the active site residues are compared between the present structure and the E. coli adenylate kinase/Ap5A structure. We failed to detect a peak in the density map corresponding to the Mg2+ ion which is required for catalysis, and its absence has been attributed to the use of ammonium sulfate in the crystallization solution. Finally, a comparison is made between the present structure and the structure of the heavy chain of muscle myosin.

A value for the Avogadro constant, NA, was derived from new measurements of the lattice parameter, the density and the molar mass of a silicon single crystal. The result NA = 6.022 135 3 × 1023 mol−1 has a relative measurement uncertainty and is in excellent agreement with other published data based on the x-ray crystal density molar mass method, indicating the high repeatability of these experiments. The value differs significantly from the Committee on Data for Science and Technology's most recent recommended value of 6.022 141 99 × 1023 mol−1 by more than 1 × 10−6 NA.