Biofactors - Volume 10, issue 1

Authors: Okar, David A. | Lange, Alex J.

Article Type: Research Article

Abstract: Fructose‐2,6‐bisphosphate is an important intracellular biofactor in the control of carbohydrate metabolic fluxes in eukaryotes. It is generated from ATP and fructose‐6‐phosphate by 6‐phosphofructo‐2‐kinase and degraded to fructose‐6‐phosphate and phosphate ion by fructose‐2,6‐bisphosphatase. In most organisms these enzymatic activities are contained in a single polypeptide. The reciprocal modulation of the kinase and bisphosphatase activities by post‐translational modifications places the level of the biofactor under the control of extra‐cellular signals. In general, these signals are generated in response to changing nutritional states, therefore, fructose‐2,6‐bisphosphate plays a role in the adaptation of organisms, and the tissues within them, to changes in environmental …and metabolic states. Although the specific mechanism of fructose‐2,6‐bisphosphate action varies between species and between tissues, most involve the allosteric activation of 6‐phosphofructo‐1‐kinase and inhibition of fructose‐1,6‐bisphosphatase. These highly conserved enzymes regulate the fructose‐6‐phosphate/fructose‐1,6‐bisphosphate cycle, and thereby, determine the carbon flux. It is by reciprocal modulation of these activities that fructose‐2,6‐bisphosphate plays a fundamental role in eukaryotic carbohydrate metabolism. Show more

Citation: Biofactors, vol. 10, no. 1, pp. 1-14, 1999

Authors: Finley, John Weldon | Davis, Cindy D.

Article Type: Research Article

Abstract: Manganese is an essential trace element that is required for the activity of several enzymes. Manganese is also quite toxic when ingested in large amounts, such as the inhalation of Mn‐laden dust by miners. This review examines Mn intake by way of the food supply and poses the question: Is there reason to be concerned with Mn toxicity or deficiency in free‐living populations in North America? Although much remains to be learned of the functions of Mn, at present there are only a few vaguely described cases of Mn deficiency in the medical literature. Given the heterogeneity of the North …American food supply, it is difficult to see the possibility of more than greatly isolated and unique instances of Mn deficiency. However, low Mn‐dependent superoxide dismutase activity may be associated with cancer susceptibility, and deserves further study. There may be reasons, however, to be concerned about Mn toxicity under some very specialized conditions. Increasing numbers of young people are adopting a vegetarian lifestyle which may greatly increase Mn intake. Iron deficiency may increase Mn absorption and further increase the body‐burden of Mn, especially in vegetarians. Mn is eliminated primarily through the bile, and hepatic dysfunction could depress Mn excretion and further contribute to the body burden. Would such a combination of events predispose substantial numbers of people to chronic Mn toxicity? At present, there is no definite proof of this occurring, but given the state of knowledge at the present time, more studies with longer time‐frames and more sensitive methods of analysis are needed. Show more

Citation: Biofactors, vol. 10, no. 1, pp. 15-24, 1999

Authors: Mittal, Rashmi A. | Tan, Chee‐Hong | Khoo, Hoon‐Eng

Article Type: Research Article

Abstract: Adenosine is known to produce biphasic effects in the renal tissues via adenosine receptors. However, the presence of more than one subtype of adenosine receptor on a type of kidney cell or tissue has not been conclusively demonstrated. To address this issue, we investigated the presence of A_{1} and A_{2} adenosine receptors in baby hamster kidney (BHK) cells by use of radioligand binding and the reverse transcription‐polymerase chain reaction. Ligand binding studies with (^{3} H)‐DPCPX revealed a single class of binding site with a K_\mathrm{D} of 9.2 \pm 2.0 nM, a …B_{\max} of 1.7 \pm 0.2 pmol/mg protein and a pharmacological profile characteristic of A_{1} adenosine receptor on the BHK cell membrane. As the presence of A_{2} adenosine receptors could not be conclusively determined by ligand binding studies, the more sensitive method of RT‐PCR was employed. The presence of A_{1} and A_\mathrm{2B} adenosine receptors was detected by RT‐PCR with specific primers and the subsequent sequencing of the resultant amplification product. The sequences obtained were 75–90% homologous to the respective adenosine receptor mRNA of rat, mouse and human. Show more

Keywords: Baby hamster, kidney, adenosine receptors, characterization, RT‐PCR

Citation: Biofactors, vol. 10, no. 1, pp. 25-33, 1999

Authors: Choi, Soo Young | Kwok, Francis | Bahn, Jae Hoon | Jeon, Seong Gyu | Ahn, Yoon Kyung | Yoon, Byung Hak | Lee, Byung Ryong | Choi, Kyung Soon | Gao, G.Z.

Article Type: Research Article

Abstract: Six monoclonal antibodies that recognize porcine brain pyridoxal kinase have been selected and designated as PK67, PK86, PK91, PK144, PK252 and PK275. A total of six monoclonal antibodies recognizing different epitopes of the enzyme were obtained, of which four inhibited the enzyme activity. When total proteins of porcine brain homogenate separated by SDS‐PAGE were subjected to monoclonal antibodies, a single reactive protein band of molecular weight 39 kDa which comigrated with purified porcine pyridoxal kinase was detected. Using the anti‐pyridoxal kinase antibodies as probes, the cross reactivities of brain pyridoxal kinase from human and other mammalian tissues and from avian …sources were also investigated. Among human and all animal tissues tested, immunoreactive bands on Western blots appeared to have the same molecular mass of 39 kDa. These results indicate that mammalian brains contain only one major type of immunologically similar pyridoxal kinase, although some properties of the enzymes reported previously differed from one another. Show more

Keywords: Pyridoxal kinase, monoclonal antibodies, pyridoxal‐5'‐phosphate, cofactor

Citation: Biofactors, vol. 10, no. 1, pp. 35-42, 1999

Authors: Thompson, Katherine H.

Article Type: Research Article

Abstract: Vanadium is an ultratrace element, widely distributed in nature, yet with no presently known specific physiological function in mammals. The apparent role of vanadium in regulation of intracellular signaling, as a cofactor of enzymes essential in energy metabolism, and as a possible therapeutic agent in diabetes is of increasing interest as more and more research reports present evidence of vanadium’s potentially unique biological function. In this mini‐review, the author summarizes current knowledge of the bioinorganic chemistry of vanadium, the basic features of diabetes mellitus and its metabolic sequelae, and the in vitro and in vivo effects of both inorganic and …organically‐chelated vanadium compounds. Results of clinical trials to date, as well as kinetic studies of tissue uptake are covered. Examples of ways to enhance the positive effects of vanadium as an oral therapeutic adjunct in diabetic control, while minimizing potential toxicity, are compared with regard to desirable features and possible drawbacks. Show more

Citation: Biofactors, vol. 10, no. 1, pp. 43-51, 1999

Authors: Johnson, W. Thomas

Article Type: Research Article

Abstract: Platelets from copper‐deficient rats have been used as a model to investigate the role of copper in receptor‐mediated cellular responses. Copper deficiency doubles the rate of dense granule secretion and increases myosin association with the platelet cytoskeleton following thrombin stimulation. Mechanisms underlying the effects of copper deficiency on thrombin‐ induced signals that elicit dense granule secretion involve suppression of protein kinase C activity and impairment of Ca^{2+} release from intracellular stores. Copper deficiency also reduces the cellular GTP content of platelets. This may limit receptor effector coupling through GTP‐dependent regulatory proteins leading to protein kinase C activation and …the release of Ca^{2+} from intracellular stores. The reduction in GTP content during copper deficiency results from its utilization to maintain cellular ATP levels in response to severely inhibited cytochrome c oxidase activity in platelet mitochondria. Thus, the role of copper in maintaining normal signal transduction may be indirectly related to its biological function in mitochondria. Show more

Citation: Biofactors, vol. 10, no. 1, pp. 53-59, 1999

Authors: Gvozdjáková, Anna | Šimko, Fedor | Kucharská, Jarmila | Braunová, Zuzana | Pšenek, Peter | Kyselovič, Ján

Article Type: Research Article

Abstract: The aim of the study was to show whether the ACE inhibitor captopril is able to protect the heart against the deleterious effect of passive cigarette smoking on left ventricular mitochondria. Four groups of rabbits were investigated: control (C), passive smoking of three cigarettes twice daily/30 minutes (S), control + captopril (7.5 mg/kg body weight twice daily) (Cap), and smoking + captopril (SCap) as in group 2 and 3. Three weeks lasting passive smoking impaired oxidative phosphorylation, diminished cytochrome oxidase activity and increased the mitochondrial F_{1} ‐ATPase protein concentration. Moreover, the level of coenzyme Q_{10} …(CoQ_{10} ) and coenzyme Q_{9 } were decreased. Simultaneous treatment with captopril prevented partly the decrease of CoQ_{10} level, deterioration of oxidative phosphorylation, diminution of cytochrome oxidase activity and enhancement of F_{1} ‐ATPase level. We conclude that captopril protected the myocardium against the harmful effect of passive smoking in rabbits. Show more

Keywords: Coenzyme Q_{10}, mitochondria, heart, passive smoking, captopril

Citation: Biofactors, vol. 10, no. 1, pp. 61-65, 1999

Authors: Navarro, J. | Maldonado, J. | Narbona, E. | Ruiz‐Bravo, A. | García Salmerón, J.L. | Molina, J.A. | Gil, A.

Article Type: Research Article

Abstract: We examined the effects of nucleotide supplementation to a preterm adapted milk formula on the lymphocyte subsets and plasma IgG, IgM and IgA levels in preterm infants for the first three months of life. Two groups of preterm infants received a milk formula or the same formula supplemented with CMP, AMP, UMP, GMP and IMP to mimic the concentration of acid‐soluble nucleotides found in human milk. Blood samples were obtained at birth, 10 days, 20–30 days and 3 months of age. Preterm infants fed the nucleotide formula exhibited higher plasma levels of IgM in all postnatal study periods than neonates …fed the standard formula; moreover, IgA was also higher at 3 months of age in nucleotide formula fed infants. No major differences were seen between groups for IgG levels and lymphocyte subsets. Thus, dietary nucleotides appear to exert actions on immature human neonate lymphocytes enhancing the in vivo production of Ig which may have a role in the defense capacity of neonates. Show more

Citation: Biofactors, vol. 10, no. 1, pp. 67-76, 1999

Article Type: Other

Citation: Biofactors, vol. 10, no. 1, pp. 77-82, 1999