Acetyl-CoA carboxylase (ACC) catalyses the formation of malonyl-CoA, an essential substrate for fatty acid synthesis in lipogenic tissues and a key regulatory molecule in muscle, brain and other tissues. ACC contributes importantly to the overall control of energy metabolism and has provided an important model to explore mechanisms of enzyme control and hormone action. Mammalian ACCs are multifunctional dimeric proteins (530-560 kDa) with the potential to further polymerize and engage in multiprotein complexes. The enzymatic properties of ACC are complex, especially considering the two active sites, essential catalytic biotin, the three-substrate reaction and effects of allosteric ligands. The expression of the two major isoforms and splice variants of mammalian ACC is tissue-specific and responsive to hormones and nutritional status. Key regulatory elements and cognate transcription factors are still being defined. ACC specific activity is also rapidly modulated, being increased in response to insulin and decreased following exposure of cells to catabolic hormones or environmental stress. The acute control of ACC activity is the product of integrated changes in substrate supply, allosteric ligands, the phosphorylation of multiple serine residues and interactions with other proteins. This review traces the path and implications of studies initiated with Dick Denton in Bristol in the late 1970s, through to current proteomic and other approaches that have been consistently challenging and immensely rewarding.

Background: Ion selectivity of voltage-gated channels is governed by selectivity filters. Results: Alternative turret region in domain II promotes highly sodium-permeable T-type channels without major changes to gating and kinetic features. Conclusion: T-type channels can generate variable sodium or calcium permeability by gene splicing. Significance: Ion selectivity in T-type channels can be altered using extracellular domains outside the ion selectivity filter.

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Acetyl-CoA carboxylase (ACC) catalyses the formation of malonyl-CoA, an essential substrate for fatty acid synthesis in lipogenic tissues and a key regulatory molecule in muscle, brain and other tissues. ACC contributes importantly to the overall control of energy metabolism and has provided an important model to explore mechanisms of enzyme control and hormone action. Mammalian ACCs are multifunctional dimeric proteins (530-560 kDa) with the potential to further polymerize and engage in multiprotein complexes. The enzymatic properties of ACC are complex, especially considering the two active sites, essential catalytic biotin, the three-substrate reaction and effects of allosteric ligands. The expression of the two major isoforms and splice variants of mammalian ACC is tissue-specific and responsive to hormones and nutritional status. Key regulatory elements and cognate transcription factors are still being defined. ACC specific activity is also rapidly modulated, being increased in response to insulin and decreased following exposure of cells to catabolic hormones or environmental stress. The acute control of ACC activity is the product of integrated changes in substrate supply, allosteric ligands, the phosphorylation of multiple serine residues and interactions with other proteins. This review traces the path and implications of studies initiated with Dick Denton in Bristol in the late 1970s, through to current proteomic and other approaches that have been consistently challenging and immensely rewarding.

While balafilcon A released the most drug from the silicone hydrogel materials, all materials released the drug too quickly to be effective as drug delivery devices.

NSCaTE is a short linear motif of (xWxxx(I or L)xxxx), composed of residues with a high helix-forming propensity within a mostly disordered N-terminus that is conserved in L-type calcium channels from protostome invertebrates to humans. NSCaTE is an optional, lower affinity and calcium-sensitive binding site for calmodulin (CaM) which competes for CaM binding with a more ancient, C-terminal IQ domain on L-type channels. CaM bound to N- and C- terminal tails serve as dual detectors to changing intracellular Ca2+ concentrations, promoting calcium-dependent inactivation of L-type calcium channels. NSCaTE is absent in some arthropod species, and is also lacking in vertebrate L-type isoforms, Cav1.1 and Cav1.4 channels. The pervasiveness of a methionine just downstream from NSCaTE suggests that L-type channels could generate alternative N-termini lacking NSCaTE through the choice of translational start sites. Long N-terminus with an NSCaTE motif in L-type calcium channel homolog LCav1 from pond snail Lymnaea stagnalis has a faster calcium-dependent inactivation than a shortened N-termini lacking NSCaTE. NSCaTE effects are present in low concentrations of internal buffer (0.5 mM EGTA), but disappears in high buffer conditions (10 mM EGTA). Snail and mammalian NSCaTE have an alpha-helical propensity upon binding Ca2+-CaM and can saturate both CaM N-terminal and C-terminal domains in the absence of a competing IQ motif. NSCaTE evolved in ancestors of the first animals with internal organs for promoting a more rapid, calcium-sensitive inactivation of L-type channels.

Acetyl-CoA carboxylase (ACC; EC 6.4.1.2) catalyses the formation of malonyl-CoA, which is essential as a metabolic substrate and as a modulator of specific protein activity. Malonyl-CoA is a substrate for fatty acid synthase (FAS), for polyketide synthases (in plants, fungi and bacteria) and for fatty acyl chain-elongation systems. As an allosteric modulator, malonyl-CoA potently inhibits carnitine palmitoyltransferase-I (CPT-I), with far-reaching effects on intermediary metabolism and cell secretory functions. ACC contributes importantly to flux control in fatty acid biosynthesis and b-oxidation and is subject to a range of interacting mechanisms that dictate tissue-specific expression and specific enzyme activity. Detailed reviews of ACC enzymology appeared in the late 1980s [l-31, so we focus on selected developments since 1990, with most emphasis on the properties of the mammalian multifunctional ACC polypeptides. We discuss the structure and regulation of the ACC genes only briefly, since these aspects are dealt with elsewhere [4]. ACC reaction and mechanismThe overall reaction catalysed by ACC is a twostep process that involves ATP-dependent formation of carboxybiotin followed by transfer of the carboxyl moiety to acetyl-CoA to form malonyl-CoA. ACCs possess distinct active sites for biotin carboxylation and for carboxyl transfer together with a 'mobile' biotin that acts as a carboxyl carrier between the two active sites. The first half-reaction of biotin carboxylation probably involves initial biotin-independent activation of bicarbonate, because ATP/ADP nucleotide exchange is not inhibited by avidin and a formal carboxy-phosphate intermediate has been Abbreviations used: ACC, acetyl-CoA carboxylase; FAS, fatty acid synthase; CPT-I, carnitine palmitoyl transferase I; BCCP, biotin carboxyl carrier protein; AMP-PK, AMP-activated protein kinase; PKA, CAMPdependent protein kinase; MAP, mitogen-activated protein; JNK, c J u n N-terminal kinase; PI 3-K, phosphatidylinositol 3-OH kinase; ERK, extracellular signal-related protein kinase. 'To whom correspondence should be addressed. observed, at least in studies with pyruvate carboxylase [5,6]. The carboxyl transferase halfreaction proceeds via proton extraction, which generates a reactive carbanion on the methyl carbon of acetyl-CoA [7]. Detailed structural studies, which are most advanced for the Escherichiu coli ACC subunits, should provide further definition of the details of the ACC reaction mechanisms [8]. Roles of ACCBiotin-dependent carboxylases emerged early in evolution and are well conserved between eubacteria, unicellular eukaryotes, plants and animals. The importance of malonyl-CoA in cell metabolism is most directly reflected by the fact that ACC expression is essential for normal growth of bacteria, yeast and isolated animal cells in culture. For example, diploid yeast cells deficient in ACC show aberrant mitosis [9], and corresponding haploid spores fail to enter vegetative growth [lo]. Specific ablation of the ACC gene in animals has not yet been r...

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