[en] The R and D work to establish a facility for the study of homogeneity and fuel density i.e., quantity of /sup 235/U in the locally fabricated LEU fuel plates for Pakistan Atomic Research Reactor (PARR-1) has been initiated. This brief report presents the results of our preliminary study in respect of homogeneity of the fuel plate constituents. An elementary experimental facility for nuclear radiation detection with Nal detector has been established. The fuel plate (U/sub 3/Si/sub 2/-AI) was manually scanned and the transmission of gamma radiation from radioactive /sup 241/Am source was determined. The study revealed encouraging results about density distribution of the plate constituents. At the same time it has also lead to future improving steps. (author)

No abstract available

[en] The conversion of androgens into estrogen involves three distinct generic reactions which are catalyzed by a single P450 enzyme (aromatase or P450(aromatase)). The first step in the process is the conversion of 19-methyl into a hydroxymethyl group which requires NADPH + O2, thus representing the well-known hydroxylation process. The next stage, converting the -CH2OH into -CHO, also requires NADPH + O2 and may be rationalized either through a second hydroxylation reaction producing a gem-diol, CH(OH)2 (which dehydrates to the aldehyde), or via another route. The final stage in the process again uses NADPH + O2, culminating in the release of C-19 as formate. Our extensive studies using precursors containing 2H, 3H, and 18O have shown that the carbonyl oxygen of the 19-aldehyde group is the one that was introduced in the first step as the hydroxyl group. The aldehydic oxygen along with another, from O2, used in the third step of the process, is incorporated into the released formate. It was found that at each stage of the process, oxygen atoms were introduced or transferred as whole numbers. In light of these data, mechanisms in which H2O is used to promote the C-10-C-19 bond cleavage or those in which the conversion of the 19-oxoandrostenedione into estrogen is considered to occur via the sequence -CHO----(-)CH(OH)2----estrogen are eliminated. In addition, our mechanistic analysis makes it unlikely that 1 beta-, 2 beta-, or 10 beta-hydroxysteroids serve as intermediates in estrogen biosynthesis. We consider a free radical mechanism for the hydroxylation process. 40 references

[en] New dentary material of Percrocuta carnifex (Pilgrim, 1913) from the Nagri Formation ofHasnot, Pakistan, is described. Specimens of this species from the Siwalik continental deposits described by previous authors are discussed in detail. In addition to the taxonomic description of the new material, the occurrence and stratigraphic position of this species within the Siwalik Hills are re-evaluated. Except for the holotype, the specimens assigned to this species are very fragmentary. The newly discovered material, a right mandibular ramus containing teeth, is the best preserved specimen found to date. The comparative analysis, based on tooth morphology and dimensions of previously reported specimens and of the specimen studied here, suggests that this species is restricted to the Chinji and Nagri formations. Finally, the dental morphological features of the studied specimen and those of other species of Percrocuta are compared, and then the phylogenetic relationship between these species is discussed. The described specimen is thus important for the taxonomic, stratigraphic and phylogenetic knowledge of P. carnifex from the Siwaliks.

[en] The high-resolution ¹³C NMR spectrum of bacteriochlorophyll a biosynthesized from [1-¹³C,1,1,4-¹⁸O₃]-5-aminolevulinic acid by growing cells of Rhodopseudomonas sphaeroides has shown both the C-17³ and C-13³ resonances consist of three additional components upfield shifted from the -¹⁶O- ¹³C double bond ¹⁶O resonance. By comparison with the ¹³C NMR spectrum obtained for phytyl acetate containing ¹³C and ¹⁸O selectively in the ester linkage, these components have been identified as the bridge (-¹⁸O- ¹³C double bond ¹⁶O), non bridge (-¹⁶O-¹³C double bond ¹⁸O), and dual-labeled (-¹⁸O-¹³C double bond ¹⁸O) isotopomers, These results have been interpreted to suggest that both the ester bonds of bacteriochlorophyll a are produced by a carboxy-alklyl transfer process

[en] The Passive Quality Control data of 31 batches of T3, 56 batches of T4, 28 batches of TSH, 8 batches of free T3 and 7 batches of free T4 RIA over a duration of one year were collected to estimate the overall reproducibility of results and level of error observed in assays employing Amersham RIA kits. The parameters recorded were: standard and unknown scatter, RER (response error relationship) parameters, standard curve parameters and quality control pool results. Cumulative RER and IP plots were drawn using individual batch data to estimate inter batch variation of error. The data analysis was performed on IBM-compatible computer using programme supplied by IAEA. Overall random error (non-counting statistics %CV) in all replicate counts was less than 7%. Mean RER parameters also suggest an overall low level of random errors in all assays. The individual batch RER's do not cross 10% error limit. This shows that random errors in out assays are not affecting the assay performance. A view of average imprecision profiles show that T3 and T4 RIA's are highly precise. TSH assay is relatively more imprecise in the normal range. FT3-RIA gives acceptable precision. In FT4-RIA the error is greater than 10%. A comparison of the overall between batch scatter (random variation) of curve parameters shows that parameters of T4 RIA's are most reproducible. Parameters of T3, TSH and FT4 RIA's have intermediate reproducibility, whereas FT3-RIA parameters are least reproducible. A comparison of BBCV's of quality Control results shows that T4-RIA is giving most reproducible results. T3, TSH and FT3 RIA's have intermediate reproducibility. FT4-RIA is least reproducible. Assays of each category show a negative drift except FT3-RIA where a positive trend is dominant. The average values of drift are within 10% limit. It is concluded that T4-RIA stands at the top as far as assay performance is concerned. (author)

No abstract available

[en] In order to replace the use of expensive Radioimmunassay (RIA) kits/bulk reagents with local technology, work with production of T3-antibodies in rabbits and measurement of antibody titres was started. The avidity of antibody with maximum tire (1:7900, determined from scatchard plot was suitably high i.e. 0.7x10/sup 10) lit/mole. Coupling of this antibody to activated cellulose was done to prepare solid phase binding agent. A solid phase radioimmunoassay was then developed. Analysis of bound sample results correlate linearly with house of commercial RIA kits and imported bulk reagents (NETRIA, U.K.). Observed sensitivity of assay (0.2 nmol/l) compares well with commercial assays. Initially obtained high imprecision at low doses was improved with experience replacement of tracer. Between batch analysis quality control results shows that in house assay is as good in quality as the commercial ones. (author)

[en] L-Methionine decarboxylase from the male fern Dryopteris filix-mas has been purified 256-fold from acetone powder extracts to very near homogeneity. The enzyme is membrane-associated and requires detergent for solubilization during the initial extraction. The enzyme is a homodimer of subunit M_r 57,000 and shows a pH optimum at ∼ 5.0 with 20 mM (2S)-methionine as substrate. A wide range of straight- and branched-chain (2S)-alkylamino acids are substrates for the enzyme. The values for the rate of decarboxylation, V_max, and for the apparent Michaelis constant, K_m, however, vary with structure and with the chirality at C-3. The pH dependence of V and V/K has been examined for three substrates: (2S)-methionine, valine, and leucine. The occurrence of the abortive reaction was confirmed by showing that [³⁵S]methionine is converted to labeled 3-(methylthio)propionaldehyde while [4'-³H]PLP is converted to labeled pyridoxamine 5'-phosphate (PMP). The decarboxylation of (2S)-methionine gave 3(methylthio)-1-aminopropane. Preparation of the N-camphanamide derivative of the amine allowed the C-1 methylene protons to be distinguished by ¹H NMR spectroscopy. Synthetic samples of the camphanamide were prepared in which each of the C-1 methylene protons was replaced by deuterium. When tritiated pyridoxal phosphate was incubated with the enzyme, tritiated pyridoxamine phosphate was formed. These results are used to construct possible mechanistic schemes for both reactions, decarboxylation and transamination. The position and possible identities of active-site proton donors are discussed

[en] L-Methionine decarboxylase from Dryopteris filix-mas catalyzes the decarboxylation of L-methionine and a range of straight- and branched-chain L-amino acids to give the corresponding amine products. The deuterium solvent isotope effects for the decarboxylation of (2S)-methionine are ^D(V/K) = 6.5 and ^DV = 2.3, for (2S)-valine are ^D(V/K) = 1.9 and ^DV = 2.6, and for (2S)-lecuine are ^D(V/K) = 2.5 and ^DV = 1.0 at pL 5.5. At pL 6.0 and above, where the value of k_cat for all of the substrates is low, the solvent isotope effects on V_max for methionine are 1.1-1.2 whereas the effects on V/K remain unchanged, indicating that the solvent-sensitive transition state occurs before the first irreversible step, carbon dioxide desorption. At very high concentration, the product amine can promote transamination of the coenzyme. However, the reaction occurs infrequently and does not influence the partitioning between decarboxylation and substrate-mediated abortive transamination under steady-state turnover conditions. The partition ratio, normal catalytic versus abortive events, can be determined from the amount of substrate consumed by a known amount of enzyme at infinite time, and the rate of inactivation can be determined by measuring the decrease in enzyme activity with respect to time. Experiments conducted in deuterium oxide allowed the solvent isotope effects for the partition ratio and the abortive reaction to be determined. ¹H NMR spectroscopic analysis of 3-(methylthio)-1-aminopropane isolated from incubations conducted in 50 molar % deuterium oxide at pL 4.8 and at pL 6.5 indicated that the proton donor was monoprotic and, therefore, is probably the imidazolium side chain of a histidine residue