Adolescent Trajectories of Aerobic Fitness and Adiposity as Markers of Cardiometabolic Risk in Adulthood.

Purpose: The aim of this study was to investigate whether adolescent growth trajectories of aerobic fitness and adiposity were associated with mid-adulthood cardiometabolic risk (CMR). Methods: Participants were drawn from the Saskatchewan Growth and Development Study (1963-1973). Adolescent growth trajectories for maximal aerobic capacity (absolute VO2 (AbsVO2)), skinfolds (SF), representing total body (Sum6SF) and central adiposity (TrunkSF), and body mass index (BMI) were determined from 7 to 17 years of age. In mid-adulthood (40 to 50 years of age), 61 individuals (23 females) returned for follow-ups. A CMR score was calculated to group participants as displaying either high or a low CMR. Multilevel hierarchical models were constructed, comparing the adolescent growth trajectories of AbsVO2, Sum6SF, TrunkSF, and BMI between CMR groupings. Results: There were no significant differences in the adolescent development of AbsVO2, Sum6SF, TrunkSF, and BMI between adult CMR groupings (p > 0.05). Individuals with high CMR accrued 62% greater adjusted total body fat percentage from adolescence to adulthood (p=0.03). Conclusions: Growth trajectories of adolescent aerobic fitness and adiposity do not appear to be associated with mid-adulthood CMR. Individuals should be encouraged to participate in behaviours that promote healthy aerobic fitness and adiposity levels throughout life to reduce lifelong CMR.

A longitudinal study of bone area, content, density, and strength development at the radius and tibia in children 4-12 years of age exposed to recreational gymnastics.

UNLABELLED: This study investigated the long-term relationship between the exposure to childhood recreational gymnastics and bone measures and bone strength parameters at the radius and tibia. It was observed that individuals exposed to recreational gymnastics had significantly greater total bone content and area at the distal radius. No differences were observed at the tibia. INTRODUCTION: This study investigated the relationship between exposure to early childhood recreational gymnastics with bone measures and bone strength development at the radius and tibia. METHODS: One hundred twenty seven children (59 male, 68 female) involved in either recreational gymnastics (gymnasts) or other recreational sports (non-gymnasts) between 4 and 6 years of age were recruited. Peripheral quantitative computed tomography (pQCT) scans of their distal and shaft sites of the forearm and leg were obtained over 3 years, covering the ages of 4-12 years at study completion. Multilevel random effects models were constructed to assess differences in the development of bone measures and bone strength measures between those exposed and not exposed to gymnastics while controlling for age, limb length, weight, physical activity, muscle area, sex, and hours of training. RESULTS: Once age, limb length, weight, muscle area, physical activity, sex, and hours of training effects were controlled, it was observed that individuals exposed to recreational gymnastics had significantly greater total bone area (18.0 ± 7.5 mm(2)) and total bone content (6.0 ± 3.0 mg/mm) at the distal radius (p < 0.05). This represents an 8-21 % benefit in ToA and 8-15 % benefit to ToC from 4 to 12 years of age. Exposure to recreational gymnastics had no significant effect on bone measures at the radius shaft or at the tibia (p > 0.05). CONCLUSIONS: Exposure to early life recreational gymnastics provides skeletal benefits to distal radius bone content and area. Thus, childhood recreational gymnastics exposure may be advantageous to bone development at the wrist.

Does lean tissue mass accrual during adolescence influence bone structural strength at the proximal femur in young adulthood?

UNLABELLED: The purpose of this study was to identify whether young adult bone structural strength at the hip is associated with adolescent lean tissue mass (LTM) accrual. It was observed that those individuals who accrued more LTM from adolescence to adulthood had significantly greater adult bone structural strength at the hip. INTRODUCTION: The purpose of this study was to identify whether young adult bone cross-sectional area (CSA), section modulus (Z), and outer diameter (OD) at the hip were associated with adolescent LTM accrual. METHODS: One hundred three young adult participants (55 males, 48 females) were tertiled into adolescent LTM accrual groupings. LTM accrual was assessed by serial measures using dual energy X-ray absorptiometry (DXA) from adolescence to young adulthood (21.3 ± 1.3 years). CSA, Z, and OD at the narrow neck (NN) and femoral shaft (S) sites of the proximal femur were assessed in young adulthood (21.3 ± 4.5 years), using hip structural analysis. Group differences were assessed using an analysis of covariance, controlling for adult height, weight, sex, and physical activity levels. RESULTS: It was found that individuals with higher adjusted adolescent LTM accrual had significantly greater adult adjusted values of NNCSA (2.49 ± 0.06 vs 2.77 ± 0.07 cm(2)), NN Z (1.18 ± 0.04 vs 1.37 ± 0.04 cm(3)), NN OD (3.07 ± 0.04 vs 3.21 ± 0.04 cm), SCSA (3.45 ± 0.08 vs 3.88 ± 0.09 cm(3)), and SZ (1.77 ± 0.05 vs 2.00 ± 0.05 cm(3)) than individuals with lower LTM accrual (p < 0.05). CONCLUSIONS: These findings suggest that the amount of LTM accrued from adolescence to young adulthood has a positive influence on adult bone structural strength at the proximal femur.

Tracking of aerobic fitness from adolescence to mid-adulthood.

BACKGROUND: Although adults' aerobic fitness is known to be correlated with cardiovascular disease risk, the longitudinal relationship with adolescent aerobic fitness is poorly described. AIM: To longitudinally investigate the relationship between aerobic fitness during adolescence and adulthood. SUBJECTS AND METHODS: Participants (207 boys, 149 girls) aged 7-17 years performed annual measures of VO2peak. In adulthood (40 and 50 years), 78 individuals (59 males and 18 females) were reassessed. Serial height measurements were used to estimate age at peak height velocity (APHV). During adolescence, VO2peak was measured via a treadmill test to voluntary exhaustion; adult VO2peak was assessed using submaximal predictive tests. Correlations were tested using Spearman's rho. ANCOVA was used to assess adult VO2peak group differences based off APHV VO2peak groupings (low, average or high). RESULTS: When sexes were pooled, moderate tracking existed from 2 years prior to APHV to APHV and APHV to 2 years after APHV (0.46, p < 0.001 and 0.35, p < 0.01, respectively). Correlations between APHV and adult values were low when sexes were pooled (p < 0.05). Comparisons of aggregated sexes revealed the low adolescent VO2peak group had lower values in adulthood relative to other groups (p < 0.05). CONCLUSION: Aerobic fitness has a low tracking between APHV and adulthood.

Using membrane stress to our advantage.

The nature of the bilayer motif coupled with the ability of lipids and proteins to diffuse freely through this structure is crucial to the viability of cells and their ability to compartmentalize domains contained therein. It seems surprising to find then that biological as well as model membranes exist in a dynamic state of mechanical stress. The stresses within such membranes are surprisingly large, typically reaching up to 50 atm (1 atm=101.325 kPa) at the core of the membrane and vary as a function of depth. The uneven distribution of lateral pressures within monolayer leaflets causes them to bend away from or towards the water interface. This can result in the formation of complex, self-assembled mesophases, many of which occur in vivo. Our knowledge of the principles underlying membrane mechanics has reached the point where we are now able to manipulate them and create nano-structures with reasonable predictability. In addition, they can be used both to explain and control the partitioning of amphipathic proteins on to membranes. The dependence of the dynamics of membrane-bound proteins and the chemical reactivity of amphipathic drug molecules on membrane stresses suggests that Nature itself takes advantage of this. Understanding and manipulating these internal forces will be a key element in creating self-assembled, biocompatible, nanoscale cell-like systems.

Role of calcium-independent phospholipases (iPLA(2)) in phosphatidylcholine metabolism.

The proposed role of calcium-independent phospholipase A(2) (iPLA(2)) in membrane phospholipid homeostasis was tested by examining the perturbation of phosphatidylcholine metabolism by enzyme overexpression. There are alternatively spliced forms of murine iPLA(2) that were widely expressed in mouse tissues: a long form containing exon-9 that is membrane-associated and a short form lacking exon-9 that is distributed between the membrane and cytosolic fractions. Enforced expression of either iPLA(2) isoform led to a significant increase in intracellular free fatty acid, lysophosphatidylcholine, and GPC without a concomitant increase in the incorporation of either exogenous arachidonic acid or choline. The accumulation of lysophosphatidylcholine in iPLA(2)-expressing cells illustrates the limited capacity of cells for reacylation and degradation of lysophospholipids. Since iPLA(2) overexpression did not accelerate either phospholipid remodeling or phosphatidylcholine synthesis, this enzyme does play a determinant (rate-controlling?) role in either of these cellular processes.

The licC gene of Streptococcus pneumoniae encodes a CTP:phosphocholine cytidylyltransferase.

The licC gene product of Streptococcus pneumoniae was expressed and characterized. LicC is a nucleoside triphosphate transferase family member and possesses CTP:phosphocholine cytidylyltransferase activity. Phosphoethanolamine is a poor substrate. The LicC protein plays a role in the biosynthesis of the phosphocholine-derivatized cell wall constituents that are critical for cell separation and pathogenesis.

Lipid activation of CTP: phosphocholine cytidylyltransferase alpha: characterization and identification of a second activation domain.

The CTP:phosphocholine cytidylyltransferase (CCT) governs the rate of phosphatidylcholine (PtdCho) biosynthesis, and its activity is governed by interaction with membrane lipids. The carboxy-terminus was dissected to delineate the minimum sequences required for lipid responsiveness. The helical domain is recognized as a site of lipid interaction, and all three tandem alpha-helical repeats from residues 257 through 290 were found to be required for regulation of enzymatic activity by this domain. Truncation of the carboxy-terminus to remove one or more of the alpha-helical repeats yielded catalytically compromised proteins that were not responsive to lipids but retained sufficient activity to accelerate PtdCho biosynthesis when overexpressed in vivo. The role of the helical region in lipid-activation was tested further by excising residues 257 through 309 to yield a protein that retained a 57-residue carboxy terminal domain fused to the catalytic core. This construct tested the hypothesis that the helical region inhibits activity in the absence of lipid rather than activates the enzyme in the presence of lipid. This hypothesis predicts constitutive activity for CCTalpha[Delta257-309]; however, this protein was tightly regulated by lipid with activities comparable to the full-length CCTalpha, in both the absence and presence of lipid. Activation of CCTalpha[Delta257-309] was dependent exclusively on anionic lipids, whereas full-length CCTalpha responded to either anionic or neutral lipids. Phosphatidic acid delivered in Triton X-100 micelles was the preferred activator of the second lipid-activation domain. These data demonstrate that CCTalpha can be regulated by lipids by two independent domains: (i) the three amphipathic alpha-helical repeats that interact with both neutral and anionic lipid mixtures and (ii) the last 57 residues that interact with anionic lipids. The results show that both domains are inhibitory in the absence of lipid and activating in the presence of lipid. Removal of both domains results in a nonresponsive, dysregulated enzyme with reduced activity. The data also demonstrate for the first time that the 57-residue carboxy-terminal domain in CCTalpha participates in lipid-mediated regulation and is sufficient for maximum activation of enzyme activity.

Overexpression of a mammalian ethanolamine-specific kinase accelerates the CDP-ethanolamine pathway.

Ethanolamine kinase (EKI) is the first committed step in phosphatidylethanolamine (PtdEtn) biosynthesis via the CDP-ethanolamine pathway. We identify a human cDNA encoding an ethanolamine-specific kinase EKI1 and the structure of the EKI1 gene located on chromosome 12. EKI1 overexpression in COS-7 cells results in a 170-fold increase in ethanolamine kinase-specific activity and accelerates the rate of [3H]ethanolamine incorporation into PtdEtn as a function of the ethanolamine concentration in the culture medium. Acceleration of the CDP-ethanolamine pathway does not result in elevated cellular PtdEtn levels, but rather the excess PtdEtn is degraded to glycerophosphoethanolamine. EKI1 has negligible choline kinase activity in vitro and does not influence phosphatidylcholine biosynthesis. Acceleration of the CDP-ethanolamine pathway also does not change the rate of PtdEtn formation via the decarboxylation of phosphatidylserine. The data demonstrate the existence of separate ethanolamine and choline kinases in mammals and show that ethanolamine kinase can be a rate-controlling step in PtdEtn biosynthesis.

Regulation of mammalian cell membrane biosynthesis.

This review explores current information on the interrelationship between phospholipid biochemistry and cell biology. Phosphatidylcholine is the most abundant phospholipid and it biosynthesis has been studied extensively. The choline cytidylyltransferase regulates phosphatidylcholine production, and recent advances in our understanding of the mechanisms that govern cytidylyltransferase include the discovery of multiple isoforms and a more complete understanding of the lipid regulation of enzyme activity. Similarities between phosphatidylcholine formation and the phosphatidylethanolamine and phosphatidylinositol biosynthetic pathways are discussed, together with current insight into control mechanisms. Membrane phospholipid doubling during cell cycle progression is a function of periodic biosynthesis and degradation. Membrane homeostasis is maintained by a phospholipase A-mediated degradation of excess phospholipid, whereas insufficient phosphatidylcholine triggers apoptosis in cells.

Macrophages deficient in CTP:Phosphocholine cytidylyltransferase-alpha are viable under normal culture conditions but are highly susceptible to free cholesterol-induced death. Molecular genetic evidence that the induction of phosphatidylcholine biosynthesis in free cholesterol-loaded macrophages is an adaptive response.

Macrophages in atherosclerotic lesions accumulate excess free cholesterol (FC) and phospholipid. Because excess FC is toxic to macrophages, these observations may have relevance to macrophage death and necrosis in atheromata. Previous work by us showed that at early stages of FC loading, when macrophages are still healthy, there is activation of the phosphatidylcholine (PC) biosynthetic enzyme, CTP:phosphocholine cytidylyltransferase (CT), and accumulation of PC mass. We hypothesized that this is an adaptive response, albeit transient, that prevents the FC:PC ratio from reaching a toxic level. To test this hypothesis directly, we created mice with macrophage-targeted disruption of the major CT gene, CTalpha, using the Cre-lox system. Surprisingly, the number of peritoneal macrophages harvested from CTalpha-deficient mice and their overall health under normal culture conditions appeared normal. Moreover, CT activity and PC biosynthesis and in vitro CT activity were decreased by 70-90% but were not absent. As a likely explanation of this residual activity, we showed that CTbeta2, a form of CT that arises from another gene, is induced in CTalpha-deficient macrophages. To test our hypothesis that increased PC biosynthesis is an adaptive response to FC loading, the viability of wild-type versus CTalpha-deficient macrophages under control and FC-loading conditions was compared. After 5 h of FC loading, death increased from 0.7% to only 2.0% in wild-type macrophages but from 0. 9% to 29.5% in CTalpha-deficient macrophages. These data offer the first molecular genetic evidence that activation of CTalpha and induction of PC biosynthesis in FC-loaded macrophages is an adaptive response. Furthermore, the data reveal that CTbeta2 in macrophages is induced in the absence of CTalpha and that a low level of residual CT activity, presumably due to CTbeta2, is enough to keep the cells viable in the peritoneum in vivo and under normal culture conditions.

Modulation of CTP:phosphocholine cytidylyltransferase by membrane curvature elastic stress.

The activity of CTP:phosphocholine cytidylyltransferase, a rate-limiting enzyme in phosphatidylcholine biosynthesis, is modulated by its interaction with lipid bilayers [Kent, C. (1997) Biochim. Biophys. Acta 1348, 79-90]. Its regulation is of central importance in the maintenance of membrane lipid homeostasis. Here we show evidence that the stored curvature elastic stress in the lipid membrane's monolayer modulates the activity of CTP:phosphocholine cytidylyltransferase. Our results show how a purely physical feedback signal could play a key role in the control of membrane lipid synthesis.

Structural basis for the feedback regulation of Escherichia coli pantothenate kinase by coenzyme A.

Pantothenate kinase (PanK) is a key regulatory enzyme in the coenzyme A (CoA) biosynthetic pathway and catalyzes the phosphorylation of pantothenic acid to form phosphopantothenate. CoA is a feedback inhibitor of PanK activity by competitive binding to the ATP site. The structures of the Escherichia coli enzyme, in complex with a nonhydrolyzable analogue of ATP, 5'-adenylimido-diphosphate (AMPPNP), or with CoA, were determined at 2.6 and 2.5 A, respectively. Both structures show that two dimers occupy an asymmetric unit; each subunit has a alpha/beta mononucleotide-binding fold with an extensive antiparallel coiled coil formed by two long helices along the dimerization interface. The two ligands, AMPPNP and CoA, associate with PanK in very different ways, but their phosphate binding sites overlap, explaining the kinetic competition between CoA and ATP. Residues Asp(127), His(177), and Arg(243) are proposed to be involved in catalysis, based on modeling of the pentacoordinate transition state. The more potent inhibition by CoA, compared with the CoA thioesters, is explained by a tight interaction of the CoA thiol group with the side chains of aromatic residues, which is predicted to discriminate against the CoA thioesters. The PanK structure provides the framework for a more detailed understanding of the mechanism of catalysis and feedback regulation of PanK.

Tumor necrosis factor-alpha inhibits expression of CTP:phosphocholine cytidylyltransferase.

We investigated the effects of tumor necrosis factor alpha (TNFalpha), a key cytokine involved in inflammatory lung disease, on phosphatidylcholine (PtdCho) biosynthesis in a murine alveolar type II epithelial cell line (MLE-12). TNFalpha significantly inhibited [(3)H]choline incorporation into PtdCho after 24 h of exposure. TNFalpha reduced the activity of CTP:phosphocholine cytidylyltransferase (CCT), the rate-regulatory enzyme within the CDP-choline pathway, by 40% compared with control, but it did not alter activities of choline kinase or cholinephosphotransferase. Immunoblotting revealed that TNFalpha inhibition of CCT activity was associated with a uniform decrease in the mass of CCTalpha in total cell lysates, cytosolic, microsomal, and nuclear subfractions of MLE cells. Northern blotting revealed no effects of the cytokine on steady-state levels of CCTalpha mRNA, and CCTbeta mRNA was not detected. Incorporation of [(35)S]methionine into immunoprecipitable CCTalpha protein in pulse and pulse-chase studies revealed that TNFalpha did not alter de novo synthesis of enzyme, but it substantially accelerated turnover of CCTalpha. Addition of N-acetyl-Leu-Leu-Nle-CHO (ALLN), the calpain I inhibitor, or lactacystin, the 20 S proteasome inhibitor, blocked the inhibition of PtdCho biosynthesis mediated by TNFalpha. TNFalpha-induced degradation of CCTalpha protein was partially blocked by ALLN or lactacystin. CCT was ubiquitinated, and ubiquitination increased after TNFalpha exposure. m-Calpain degraded both purified CCT and CCT in cellular extracts. Thus, TNFalpha inhibits PtdCho synthesis by modulating CCT protein stability via the ubiquitin-proteasome and calpain-mediated proteolytic pathways.

Activity of the phosphatidylcholine biosynthetic pathway modulates the distribution of fatty acids into glycerolipids in proliferating cells.

PtdCho accumulation is a periodic, S phase-specific event that is modulated in part by cell cycle-dependent fluctuations in CTP:phosphocholine cytidylyltransferase (CCT) activity. A supply of fatty acids is essential to generate the diacylglycerol (DG) precursors for phosphatidylcholine (PtdCho) biosynthesis but it is not known whether the DG supply is also coupled to the cell cycle. Although the rate of fatty acid synthesis in a macrophage cell line was dramatically stimulated in response to the growth factor, CSF-1, it was not regulated by the cell cycle. Increased fatty acid synthesis correlated with elevated acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) steady-state mRNA levels. Cellular fatty acid synthesis was essential for membrane PL synthesis. Cerulenin inhibition of endogenous fatty acid synthesis also inhibited PtdCho synthesis, which was not relieved by exogenous fatty acids. Inhibition of CCT activity by the addition of lysophosphatidylcholine (lysoPtdCho) or temperature-shift of a conditionally defective CCT diverted newly synthesized DG to the TG pool where it accumulated. Enforced expression of CCT stimulated PtdCho biosynthesis and reduced TG synthesis. Thus, the cellular DG supply did not regulate PtdCho biosynthesis and CCT activity governs the partitioning of DG into either the PL or TG pools, thereby controlling both PtdCho and TG biosynthesis.

Pantothenate kinase regulation of the intracellular concentration of coenzyme A.

Pantothenate kinase (PanK) is the key regulatory enzyme in the CoA biosynthetic pathway in bacteria and is thought to play a similar role in mammalian cells. We examined this hypothesis by identifying and characterizing two murine cDNAs that encoded PanK. The two cDNAs were predicted to arise from alternate splicing of the same gene to yield different mRNAs that encode two isoforms (mPanK1alpha and mPanK1beta) with distinct amino termini. The predicted protein sequence of mPanK1 was not related to bacterial PanK but exhibited significant similarity to Aspergillus nidulans PanK. mPanK1alpha was most highly expressed in heart and kidney, whereas mPanK1beta mRNA was detected primarily in liver and kidney. Pantothenate was the most abundant pathway component (42.8%) in normal cells providing clear evidence that pantothenate phosphorylation was a rate-controlling step in CoA biosynthesis. Enhanced mPanK1beta expression eliminated the intracellular pantothenate pool and triggered a 13-fold increase in intracellular CoA content. mPanK1beta activity in vitro was stimulated by CoA and strongly inhibited by acetyl-CoA illustrating that differential modulation of mPanK1beta activity by pathway end products also contributed to the management of CoA levels. These data support the concept that the expression and/or activity of PanK is a determining factor in the physiological regulation of the intracellular CoA concentration.

Distribution of CTP:phosphocholine cytidylyltransferase (CCT) isoforms. Identification of a new CCTbeta splice variant.

CTP:phosphocholine cytidylyltransferase is a major regulator of phosphatidylcholine biosynthesis. A single isoform, CCTalpha, has been studied extensively and a second isoform, CCTbeta, was recently identified. We identify and characterize a third cDNA, CCTbeta2, that differs from CCTbeta1 at the carboxyl-terminal end and is predicted to arise as a splice variant of the CCTbeta gene. Like CCTalpha, CCTbeta2 is heavily phosphorylated in vivo, in contrast to CCTbeta1. CCTbeta1 and CCTbeta2 mRNAs were differentially expressed by the human tissues examined, whereas CCTalpha was more uniformly represented. Using isoform-specific antibodies, both CCTbeta1 and CCTbeta2 localized to the endoplasmic reticulum of cells, in contrast to CCTalpha which resided in the nucleus in addition to associating with the endoplasmic reticulum. CCTbeta2 protein has enzymatic activity in vitro and was able to complement the temperature-sensitive cytidylyltransferase defect in CHO58 cells, just as CCTalpha and CCTbeta1 supporting proliferation at the nonpermissive conditions. Overexpression experiments did not reveal discrete physiological functions for the three isoforms that catalyze the same biochemical reaction; however, the differential cellular localization and tissue-specific distribution suggest that CCTbeta1 and CCTbeta2 may play a role that is distinct from ubiquitously expressed CCTalpha.

Cellular responses to excess phospholipid.

Phosphatidylcholine (PtdCho) is the major membrane phospholipid in mammalian cells, and its synthesis is controlled by the activity of CDP:phosphocholine cytidylyltransferase (CCT). Enforced CCT expression accelerated the rate of PtdCho synthesis. However, the amount of cellular PtdCho did not increase as a result of the turnover of both the choline and glycerol components of PtdCho. Metabolic labeling experiments demonstrated that cells compensated for elevated CCT activity by the degradation of PtdCho to glycerophosphocholine (GPC). Phospholipase D-mediated PtdCho hydrolysis and phosphocholine formation were unaffected. Most of the GPC produced in response to excess phospholipid production was secreted into the medium. Cells also degraded the excess membrane PtdCho to GPC when phospholipid formation was increased by exposure to exogenous lysophosphatidylcholine or lysophosphatidylethanolamine. The replacement of the acyl moiety at the 1-position of PtdCho with a non-hydrolyzable alkyl moiety prevented degradation to GPC. Accumulation of alkylacyl-PtdCho was associated with the inhibition of cell proliferation, demonstrating that alternative pathways of degradation will not substitute. GPC formation was blocked by bromoenol lactone, implicating the calcium-independent phospholipase A2 as a key participant in the response to excess phospholipid. Owing to the fact that PtdCho is biosynthetically converted to PtdEtn, excess PtdCho resulted in overproduction and exit of GPE as well as GPC. Thus, general membrane phospholipid homeostasis is achieved by a balance between the opposing activities of CCT and phospholipase A2.

Cloning and characterization of a eukaryotic pantothenate kinase gene (panK) from Aspergillus nidulans.

Pantothenate kinase (PanK) is the key regulatory enzyme in the CoA biosynthetic pathway. The PanK gene from Escherichia coli (coaA) has been previously cloned and the enzyme biochemically characterized; highly related genes exist in other prokaryotes. We isolated a PanK cDNA clone from the eukaryotic fungus Aspergillus nidulans by functional complementation of a temperature-sensitive E. coli PanK mutant. The cDNA clone allowed the isolation of the genomic clone and the characterization of the A. nidulans gene designated panK. The panK gene is located on chromosome 3 (linkage group III), is interrupted by three small introns, and is expressed constitutively. The amino acid sequence of A. nidulans PanK (aPanK) predicted a subunit size of 46.9 kDa and bore little resemblance to its bacterial counterpart, whereas a highly related protein was detected in the genome of Saccharomyces cerevisiae. In contrast to E. coli PanK (bPanK), which is regulated by CoA and to a lesser extent by its thioesters, aPanK activity was selectively and potently inhibited by acetyl-CoA. Acetyl-CoA inhibition of aPanK was competitive with respect to ATP. Thus, the eukaryotic PanK has a distinct primary structure and unique regulatory properties that clearly distinguish it from its prokaryotic counterpart.