Biokinetics of lead in various organs of rats using radiotracer technique

Uptake, distribution, and elimination of lead in various organs of rats have been studied using a radiotracer technique. The elimination data for various organs, except whole blood, is fitted to a double-exponential function using a computer program. The biological half-lives along with the percent elimination of lead by two different decay modes in testis, epididymis, prostate, and seminal vesicles are being reported together with that in liver, kidney, blood, and whole body. It is evident from this study that the elimination of lead is limited for all the organs and permits lead accumulation in the bone, where it is stored and becomes almost unavailable for elimination. Lead levels in blood, testis, and femur of lead acetate-fed rats measured using atomic absorption spectroscopy have been correlated to the uptake of²¹⁰Pb in various organs.     

Protein-linked isoprenoid lipids in dexamethasone-treated human lymphoid lines in culture.

Accumulation of isoprenoids was studied in two cell lines derived from acute T-cell leukemia: CEM-C7 cells, whose growth is inhibited by the glucocorticoid dexamethasone, and CEM-C1 cells, which are resistant to this steroid. Isoprenoids were measured by growing the cells in serum-free medium in the presence of lovastatin, which blocks synthesis of mevalonate, and then labeling with exogenous [3H]mevalonolactone. In both cell lines, isoprenoids associated with proteins were detected in cytoplasm, nucleus, and chromatin, and in the chromatin residue that remains after extraction of histone and nonhistone proteins. Differences in labeling were detected after treatment with dexamethasone in the CEM-C7 line, showing a decrease in the cytoplasmic fraction with a corresponding increase in both the nuclear and chromatin fractions as compared with untreated cells. No change was seen in the CEM-C1 line. In both cell lines, 25-30% of the incorporated label was released by treatment with acid or alkali. However, the majority of the label required treatment with methyl iodide for the release of organic-soluble tritiated products. After extraction with chloroform, the lipid fractions contained farnesol, geraniol, dolichols, and possibly nerolidol.     

A need for re-examination of the fibre diffraction data of A-DNA

A-DNA pattern, obtained using a flat plat camera, was indexed by Fuller $\text{et}\text{al}{}^6$ on the basis of a c-face centred monoclinic cell with a = 22.24 Å, b = 40.62 Å, c = 28.15 Å and β = 97.0°. A precession photograph of A-DNA which gives an undistorted picture of the lattice, showed that the unit cell parameters as given by Fuller $\text{et}\text{al}$ were not quite correct. The precession photograph showed a strong meridional reflection (R = 0.00 Å^?1) on the 11th layer line. But the occurrence of the meridional reflection on the 11th layer line could not be explained on the basis of the cell parameters given by Fuller $\text{et}\text{al}{}^6$; using those cell parameters the reflection which comes closest to the meridian on 11th layer line is at R = 0.025 Å^?1. However, a simple interchange of a and b values accounted for the meridional reflection on 11th layer line. The corrected cell parameter refined against 28 strong spots are a = 40.75 Å, b = 22.07 Å, c = 28.16 Å and β = 97.5°. In the new unit cell of A-DNA, the packing arrangement of the two molecules is different from that in the old one. Nonetheless, our earlier contention is again reaffirmed that both right and left-handed A-DNA are stereochemically allowed and consistent with the observed fibre pattern.     

Enzymatic control of membrane lipids inMycobacterium smegmatis ATCC 607 grown at low temperature

Enzymes of phospholipid synthesis were studied inMycobacterium smegmatis ATCC 607 grown at 37 and 27°C. The synthesis seemed to be regulated, at least partly, at the phosphatidic acid level by the specificity of the acyltransferases. The individual phospholipid species were found to be regulated at the enzymatic level in the maintenance of membrane fluidity.     

Serogenetic variation in four caste populations of Haryana, India

The phenotypes and gene frequencies of 3 blood groups, 7 red-cell enzymes and a serum protein were studied in 4 caste population groups of Haryana, North India. The results indicate that the distribution of these blood markers is rather homogeneous in the 4 groups and generally resembles that observed in various populations from neighbouring North Indian states.     

The role of hydroxyproline in collagen folding: conformational energy calculations on oligopeptides containing proline and hydroxyproline

We have observed that the rate of folding of the enzymatically hydroxylated form of poly(Gly-Pro-Pro) into the triple-helical conformation is considerably higher than that of the unhydroxylated polypeptide [R. K. Chopra and V. S. Ananthanarayanan (1982) Proc. Natl. Acad. Sci. USA 79 , 7180–7184]. In this study, we examine a plausible kinetic pathway for triple-helix formation by selecting peptide models for the unhydroxylated collagen molecule, and computing their conformational energies before and after proline hydroxylation. Starting with the available data on the preferred conformations of proline- and hydroxyproline-containing peptide sequences, energy minimization was carried out on the following pairs of peptides: Gly-Ala-Pro-Gly-Ala and Gly-Ala-Hyp-Gly-Ala; Gly-Pro-Pro-Gly-Ala and Gly-Pro-Hyp-Gly-Ala; Gly-Ala-Pro-Gly-Ala-Pro and Gly-Ala-Hyp-Gly-Ala-Hyp. It was found that, with each pair of peptides, the energetically most favorable conformation (I) has an extended structure at the Gly-Ala or Gly-Pro segment and a β-bend at the Pro-Gly or Hyp-Gly segment. In the Hyp-containing peptides, this conformation is further stabilized by a (Hyp_{i + 2})OH…OC(Gly_i) hydrogen bond. Conformation I is lower in energy by about 6–13 kcal/mol of the peptide than the fully extended conformations that resemble the single collagen polypeptide chain and contain no intramolecular hydrogen bond. In contrast to the proline counterpart, the hydroxyproline-containing peptides are found capable of adopting a partially extended conformation that does not contain the β-bend but retains the (Hyp)OH…OC(Gly) hydrogen bond. The energy of this conformation is intermediate between conformation I and the fully extended conformation. The continuation of the β-bend along the chain is restricted by stereochemical constraints that are more severe in the latter two pairs of peptides than in the first pair. Such a restriction may be considered to trigger the “unbending” of the minimum energy conformation leading to its straightening into the fully extended conformation; the latter, in turn, would lead to triple-helix formation through favorable interchain interactions. We propose that the partially extended conformation in the Hyp-containing peptides could serve as a kinetic intermediate on the way to forming the fully extended conformation. Because of the (Hyp_{i + 2})OH…OC(Gly_i) hydrogen bond, this conformation would also serve to lock the trans geometry at the Gly-Ala(Pro) and Ala(Pro)-Hyp peptide bonds, thereby enhancing the rate of their helix formation. A scheme for collagen folding in proposed on the basis of these results.     

Energetics of left and right handed models of DNA

It has been shown by model building studies that various right handed and left handed models are compatible with X-ray data of B-DNA and C-DNA. These models are also found to be in good agreement with infrared dichroism data. Detailed potential energy calculations have now been carried out for these models, viz., right and left handed B-DNA and right and left handed C-DNA. It is found that base sugar stacking and interactions involving the phosphate groups are the dominant forces for stabilizing a particular structure. For some sequences, viz., A-A, T-A and C-A, left handed stacking is quite favourable in both B and C structures. But intranucleotide interactions make the left B-DNA unfavourable while the left C-DNA structure is more stable, for all the sequences, than the right C-DNA structure, proposed from fibre data. For the hexanucleoside pentaphosphate fragments the same trend is observed, with the right handed B-DNA being the most stable of the four models studied. However, the left C-DNA structure is only marginally higher in energy, particularly if the shielding effect of the counter ions, on the phosphate group is taken into consideration.