Thiamin deposition in eggs is not dependent on riboflavin-binding protein

The thiamin content of eggs laid by hens possessing no, one or two functional genes for riboflavin-binding protein is unaffected by the genotype. This does not support the hypothesis of Muniyappa & Adiga [Biochem. J. (1979) 177, 887–894] that the deposition of thiamin-binding protein is coupled to the deposition of riboflavin-binding protein.     

Pathways and control of ketone body metabolism: on the fringe of lipid biochemistry

Ketone bodies become major body fuels during fasting and consumption of a high-fat, low-carbohydrate (ketogenic) diet. Hyperketonemia is associated with potential health benefits. Ketone body synthesis (ketogenesis) is the last recognizable step of lipid energy metabolism, a pathway that links dietary lipids and adipose triglycerides to the Krebs cycle and respiratory chain and has three highly regulated control points: (1) adipocyte lipolysis, (2) mitochondrial fatty acids entry, controlled by the inhibition of carnitine palmityl transferase I by malonyl coenzyme A (CoA) and (3) mitochondrial 3-hydroxy-3-methylglutaryl CoA synthase, which catalyzes the irreversible first step of ketone body synthesis. Each step is suppressed by an elevated circulating insulin level or insulin/glucagon ratio. The utilization of ketone bodies (ketolysis) also determines circulating ketone body levels. Consideration of ketone body metabolism reveals the mechanisms underlying the extreme fragility of dietary ketosis to carbohydrate intake and highlights areas for further study.     

Thiamin Deficiency in the Lamb: Changes in Thiamin Phosphate Esters in the Brain

: Concentrations of thiamin (unphosphorylated), thiamin monophosphate (TMP), thiamin diphosphate (TDP), and thiamin triphosphate (TTP) were measured in three regions of the brain of seven pairs of lambs. The lambs were maintained on a thiamin-free synthetic diet for 2, 3, or 4 weeks. Controls were pair-fed and supplemented with thiamin. The three brain regions were: (1) dorso-lateral aspect of the cortex [common site for lesions of polioencephalomalacia (PEM)]; (2) pyriform lobe of the cortex (no PEM lesions are found here); (3) white matter of the internal capsule (no PEM lesions found here). The concentration of TTP in all three sections of brain was maintained at control values for up to 4 weeks on the thiamin-deficient diet. TDP concentration decreased to 22% of control values in both regions of grey matter after 4 weeks on the diet. Unphosphorylated thiamin and TMP decreased to a smaller extent than TDP.     

Thiamin biofortification of crops

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The biochemistry of drug metabolism--an introduction: Part 2. Redox reactions and their enzymes

This review continues a general presentation of the metabolism of drugs and other xenobiotics started in a recent issue of Chemistry & Biodiversity. This Part 2 presents the numerous oxidoreductases involved, their nomenclature, relevant biochemical properties, catalytic mechanisms, and the very diverse reactions they catalyze. Many medicinally, environmentally, and toxicologically relevant examples are presented and discussed. Cytochromes P450 occupy a majority of the pages of Part 2, but a large number of relevant oxidoreductases are also considered, e.g., flavin-containing monooxygenases, amine oxidases, molybdenum hydroxylases, peroxidases, and the innumerable dehydrogenases/reductases.     

Structural requirements of pyrroloquinoline quinone dependent enzymatic reactions

On the basis of crystal structures of the pyrroloquinoline quinone (PQQ) dependent enzymes methanol dehydrogenase (MDH) and soluble glucose dehydrogenase (s-GDH), different catalytic mechanisms have been proposed. However, several lines of biochemical and kinetic evidence are strikingly similar for both enzymes. To resolve this discrepancy, we have compared the structures of these enzymes in complex with their natural substrates in an attempt to bring them in line with a single reaction mechanism. In both proteins, PQQ is located in the center of the molecule near the axis of pseudo-symmetry. In spite of the absence of significant sequence homology, the overall binding of PQQ in the respective active sites is similar. Hydrogen bonding interactions are made with polar protein side chains in the plane of the cofactor, whereas hydrophobic stacking interactions are important below and above PQQ. One Arg side chain and one calcium ion are ligated to the ortho-quinone group of PQQ in an identical fashion in either active site, in agreement with their proposed catalytic function of polarizing the PQQ C5-O5 bond. The substrates are bound in a similar position above PQQ and within hydrogen bond distance of the putative general bases Asp297 (MDH) and His144 (s-GDH). On the basis of these similarities, we propose that MDH and s-GDH react with their substrates through an identical mechanism, comprising general base-catalyzed hydride transfer from the substrate to PQQ and subsequent tautomerization of the PQQ intermediate to reduced PQQ.     

Thiamin biosynthesis: still yielding fascinating biological chemistry

The present paper describes the biosynthesis of the thiamin thiazole in Bacillus subtilis and Saccharomyces cerevisiae. The two pathways are quite different: in B. subtilis, the thiazole is formed by an oxidative condensation of glycine, deoxy-D-xylulose 5-phosphate and a protein thiocarboxylate, whereas, in S. cerevisiae, the thiazole is assembled from glycine, NAD and Cys205 of the thiazole synthase.     

Student reactions and learning: evaluation of a biochemistry course that uses web technology and student collaboration

Many academic institutions across the country are incorporating computer and Internet technology into their classrooms. Rensselaer has developed a studio classroom that incorporates student collaboration and Internet technology. The purpose of this research was to examine student reactions and learning in an undergraduate biochemistry course taught in a studio classroom. Student reactions to the course, the technology, and working in groups were positive. Students liked using the technology, felt it helped them to learn the material, and thought working in groups was beneficial for learning. Pre-test and post-test grades on a standardized examination indicated a significant increase in learning. In addition, positive reactions to using the technology in the course, as well as student confidence to do well in the course, were significantly related to improved course performance.     

Electron transfer and energy dependent reactions in glutaraldehyde-fixed chloroplasts

The effects of GA fixation on electron transfers in photosystemsI and II in photosynthesis and energy dependent reactions ofchloroplasts, such as changes in light scattering, H⁺ uptakeand 515-nm absorbance, were investigated. Fixation of chloroplastswith GA resulted in a lowering of the DCIP and MV photoreductions.DCIP photoreduction activity in fixed chloroplasts was not restoredin the presence of DPC, an electron donor to photosystem II,but was significantly stimulated by DPC when chloroplasts werefixed after aging. The results suggest that the inhibitory effectof GA fixation on photosystem II differs in its mechanism fromthose of treatments such as heating, Tris-washing and aging.The oxidation-reduction reaction of P700 was depressed by GAfixation. Energy dependent reactions in fixed chloroplasts were more markedlydepressed than were electron transfers. Fixed chloroplasts showeda slight conformational response in the presence of PMS. Analysis of the emission spectrum and the induction of chlorophylla fluorescence in fixed chloroplasts suggested that the twopigment systems were partially disordered and that the correspondingprimary photochemical processes were inhibited. (Received November 21, 1972; )     

Mitochondrial Uptake of Thiamin Pyrophosphate: Physiological and Cell Biological Aspects

Mammalian cells obtain vitamin B1 (thiamin) from their surrounding environment and convert it to thiamin pyrophosphate (TPP) in the cytoplasm. Most of TPP is then transported into the mitochondria via a carrier-mediated process that involves the mitochondrial thiamin pyrophosphate transporter (MTPPT). Knowledge about the physiological parameters of the MTPP-mediated uptake process, MTPPT targeting and the impact of clinical mutations in MTPPT in patients with Amish lethal microcephaly and neuropathy and bilateral striatal necrosis are not fully elucidated, and thus, were addressed in this study using custom-made ³H-TPP as a substrate and mitochondria isolated from mouse liver and human-derived liver HepG2 cells. Results showed ³H-TPP uptake by mouse liver mitochondria to be pH-independent, saturable (K_m =6.79±0.53 µM), and specific for TPP. MTPPT protein was expressed in mouse liver and HepG2 cells, and confocal images showed a human (h)MTPPT-GFP construct to be targeted to mitochondria of HepG2 cells. A serial truncation analysis revealed that all three modules of hMTPPT protein cooperated (although at different levels of efficiency) in mitochondrial targeting rather than acting autonomously as independent targeting module. Finally, the hMTPPT clinical mutants (G125S and G177A) showed proper mitochondrial targeting but displayed significant inhibition in ³H-TPP uptake and a decrease in level of expression of the MTPPT protein. These findings advance our knowledge of the physiology and cell biology of the mitochondrial TPP uptake process. The results also show that clinical mutations in the hMTPPT system impair its functionality via affecting its level of expression with no effect on its targeting to mitochondria.     

Blood biochemistry reflects seasonal nutritional and reproductive constraints in the eurasian badger (Meles meles)

Physiological responses to nutritional and reproductive constraints were explored in a wild population of Eurasian badgers (Meles meles) inhabiting Wytham Woods, Oxfordshire, United Kingdom. We compared seasonal blood levels of lipid and protein compounds to variables describing the sex, age, body condition, wounds, testes position, and flea abundance of the badgers. We found seasonal variations in albumin/globulins and urea/creatinine ratios matched by differences in body condition. High creatinine, urea, and triglycerides levels were obtained in animals in poor nutritional condition and with low levels of body fat. The maintenance of urea/creatinine ratios indicates that the badger does not demonstrate a stage of protein conservation in periods of food scarcity during the summer or periods of cold weather. Hypercholesterolaemia, especially in fat animals, was confirmed. We also offer baseline levels of metabolites commonly used in clinical biochemistry for their further use in the analysis of the status and the management of wild badger populations.