Absence of correlation between Y chromosome heterochromatin and several anthropometric measurements in a Mexican population

Summary The correlation between nine anthropometric variables and six different measurements of the Y heterochromatic regions of 146 young Mexican adults was investigated. Only the absolute heterochromatic width showed a significant correlation at the 0.02 level with the upper segment/lower segment ratio, but the biological significance of this finding is strongly questioned.     

Effect of zearalenone (F-2) on pea stem,maize root,and rat liver mitochondria

At 5 and 10 g ml^-1 concentration, zearalenone (F-2), a mycotoxin produced by a number of species of the genus Fusarium, causes an inhibition of the oxidative phosphorylation of isolated plant mitochondria, while at 20 and 40 g ml^-1 it causes uncoupling. However, when the mitochondria are pre-incubated for 20 min with F-2, the uncoupling appears to be the prevailing effect. F-2 is also able to inhibit the mitochondrial ATPase activity (Mg²⁺-dependent). Conversely, F-2 (40 g ml^-1) does not alter the ATP level of maize roots and only slightly affects the ATPase activity of pea stem and maize root microsomal fractions. In addition, F-2 (10–40 g ml^-1) inhibits ATP synthesis catalyzed by rat liver mitochondria. It is suggested that the phytotoxicity of F-2, also known for its ability to collapse the transmembrane electric potential of maize roots, may be mainly linked to its ability to increase the proton permeability of the cell, similar to the common uncouplers.Abbreviations F-2 zearalenone - DCCD N,N-dicyclohexylcarbodiimide - PCCP carbonyl cyanide, p-trifluoromethoxiphenylhydrazone - CBT Cerospora beticola toxin     

Cytogenetic studies in the genus Zea

Summary The nuclear DNA amount and the heterochromatin content in species and hybrids of Zea were analyzed in telophase nuclei (2C) of the root apex of germinating seeds. The results revealed significant differences among taxa and also among lines and races of maize. The hybrids between Z. mays ssp. mays x Z. mays ssp. mexicana (2n=20), Z. diploperennis x Z. perennis (2n=30), and Z. diploperennis x Z.perennis (2n=40) showed DNA content intermediate between that of the parents. The number of chromosomal C-bands and the proportion of the genome comprising C-band heterochromatin were positively related to genome size. In the different lines and races of maize studied, there was a positive correlation between genome size and the interval from germination to flowering. Octoploid Z. perennis (2n=40) showed the smallest DNA content per basic genome and the smallest heterochromatic blocks, suggesting that the DNA lost by this species consisted mainly of repetitive sequences. Considering that the extant species of Zea are tetraploid (2n=20) and octoploid (2n=40) and that the ancestral diploids are extinct, any consideration of the direction (increase or decrease) of the DNA change would be entirely speculative. The extant species could be the product of natural and artificial selection acting on different genotypic and nucleotypical constitutions at the diploid and/or tetraploid levels.     

Targeting of lysosomal integral membrane protein LIMP II. The tyrosine-lacking carboxyl cytoplasmic tail of LIMP II is sufficient for direct targeting to lysosomes.

Time course experiments of the localization of rat LIMP II expressed in COS cells show that the protein is transported directly from the Golgi complex to lysosomes. Substitution of the tyrosine-lacking carboxyl cytoplasmic tail of LIMP II for the native cytoplasmic tails of the plasma membrane proteins CD36 and CD8 resulted in straight transport of both proteins to lysosomes. The synthetic tyrosine-containing heptapeptide, RGTGVYG, did not replace the natural carboxyl cytoplasmic tail of LIMP II in its ability to transport both CD36 and CD8 to lysosomes, and the two constructs were transported to and expressed at the plasma membrane. Substitution of the cytoplasmic tails of either CD36 or CD8 for the carboxyl cytoplasmic tail of LIMP II resulted in transport of the mutants to the plasma membrane where they underwent endocytosis before accumulating into lysosomes. The results indicate that a motif contained in the tyrosine-lacking carboxyl cytoplasmic tail of LIMP II is sufficient to target proteins directly from the Golgi complex to lysosomes.     

Cloning, sequencing, and expression of a cDNA encoding rat LIMP II, a novel 74-kDa lysosomal membrane protein related to the surface adhesion protein CD36.

LIMP II is a glycoprotein expressed in the membrane of lysosomes and secretory granules with lysosomal properties. Sequence analysis of a CNBr-cleaved peptide allowed the synthesis of a 47-mer oligonucleotide that was used to screen a rat liver cDNA library in lambda gt11. This resulted in isolation of a 2-kilobase cDNA containing 1,434 bases encoding the entire protein. The deduced amino acid sequence indicates that LIMP II consists of 478 amino acid residues. The segment spanning residues 4-6 to 26 constitute an uncleavable signal peptide. LIMP II possesses a hydrophobic amino acid segment near the carboxyl end, that together with the uncleaved signal peptide may anchor the protein to the membrane through two distant segments. The major portion of the protein resides on the luminal side and displays 11 potential N-glycosylation sites and 5 cysteine residues. Two short cytoplasmic tails, 2-4 and 20-21 amino acids long, correspond to the NH2- and COOH-terminal ends of the protein, respectively. Transfection of COS cells with the cDNA of LIMP II resulted in expression of the protein and its transport to lysosomes. Comparison of the entire sequence to various data bases of known proteins revealed extensive homology between LIMP II and the cell surface protein CD36 involved in cell adhesion. No significant homology was detected with the two families of lysosomal membrane proteins A and B, recently described.     

The role of copper in bovine serum amine oxidase

Summary The role of copper in bovine serum amine oxidase was investigated by studying the effect of copper-binding inhibitors on the reactions of the pyrroloquinoline quinone carbonyl and on the reaction with oxygen. Hydrazines and hydrazides were used as carbonyl reagents and one of the hydrazines, benzylhydrazine, which was found to behave as a pseudo-substrate, was used to probe the reaction with oxygen. The presence ofN,N-diethyldithiocarbamate, a chelator that binds copper irreversibly, did not prevent the reactions at the carbonyl, but slowed down their rate and modified the conformation of the adducts. The same happened to the reaction with oxygen, which was slowed down but not abolished. Copper, which was never seen in the reduced state, thus appears to control all reactions without being directly involved in the binding of either hydrazines or oxygen. The enzyme functionality was in fact preserved upon substitution of copper with cobalt. The specific activity of the cobalt-substituted enzyme was only reduced to about 40% the native amine oxidase value. This is the first case so far in which the role of copper can be performed by a different metal ion.Abbreviations BSAO bovine serum amine oxidase - DDC N,N-diethyldithiocarbamate - PQQ pyrroloquinoline quinone