Oxygen-binding Heme Complexes of Peptides Designed to Mimic the Heme Environment of Myoglobin and Hemoglobin

Development of effective resuscitation agents for blood-loss replacement in trauma or surgery is extremely important despite substantial improvements in screening methods of blood from human donors. This paper reports the design and synthesis of peptides that mimic the natural environment of the heme group in myoglobin (Mb) and in the - and -subunits of human adult hemoglobin (Hb). The designs were based on the fact that the heme group in the aforementioned proteins is sandwiched between helices E and F. Fifteen test peptides and six control peptides were synthesized, and their ability to form stable complexes with heme was investigated. It was found that none of the control peptides or proteins was able to bind heme. However, each of the peptides that were designed to mimic the E--F helices, and even shorter designs, which removed from this region residues that do not contribute to contacts with the heme group, were each able to bind one mole of heme per mole of peptide forming peptide–heme complexes that were stable to manipulation and behaved as single molecular species. Oxygen binding measurements on the reduced peptide–heme complexes showed that these compounds bind oxygen and give visible spectra that were typical of oxygenated heme-proteins. In oxygen binding measurements done under different partial pressures of oxygen, the heme–peptide complexes gave hyperbolic oxygen-saturation curves, but showed slight differences in their P₅₀ values. The P₅₀ values ranged from 3.8 mmHg for the heme–peptide B7 complex to 13.7 mmHg for the heme–peptide D13 complex (under the same conditions, P₅₀ values for Hb and Mb were 34.0 and 5.5 mmHg, respectively). It is concluded that peptide constructs designed to mimic the heme-binding regions of Mb or the Hb subunits were able to form coordinate 1:1 complexes with heme, and these complexes bind oxygen in a manner expected for single subunit heme proteins.     

Ecology and management of mahogany (Swietenia macrophylla King) in the Chimanes Forest, Bed, Bolivia

Mahogany ( Swietenia macrophylla King) regenerates in areas of erosion on high terraces and in forest killed by flooding and deposition of alluvial sediments in the Chimanes Forest, Bolivia. These hydrological disturbances are patchy, and only one of five stands of mahogany that we inventoried was regenerating. Mahogany survives these disturbances significantly better than the common tree species. The long time between disturbances appears to favour late maturation. Mahogany trees allocate little photosynthates to reproduction until they are very large emergents, at least 80 cm in diameter. The episodic nature of the regeneration sites means that mahogany stands are composed of one or a few cohorts, which are vulnerable to overharvesting, particularly with the current use of a minimum cutting diameter to regulate harvest. The delayed onset of fecundity means that the small trees that escape harvest are not very fecund, resulting in minimal seed input to logged forest. Only 7–9% of the gaps created by logging contain natural regeneration after 20 + yr. A successful management plan for mahogany would entail a monocyclic harvest, with a rotation age of 100 + years, the estimated time that it takes for trees to achieve commercial size in natural forest. Since the number of seed trees that will be left is small, they should be concentrated in sites that are likely to be conducive to natural regeneration, such as near rivers and flood damaged forest. Seed production will be maximized for a given basal area (opportunity cost to loggers) if trees c. 110 cm dbh are selected as seed trees. The mahogany stocks in the Chimanes Forest are nearly exhausted, but the findings of this study could be used to help rebuild the mahogany populations, or to design management plans for the commercial species that have similar ecologies to mahogany.     

Heterogeneous binding of high mobility group chromosomal proteins to nuclei

A dramatic difference is observed in the intracellular distribution of the high mobility group (HMG) proteins when chicken embryo fibroblasts are fractionated into nucleus and cytoplasm by either mass enucleation of cytochalasin-B-treated cells or by differential centrifugation of mechanically disrupted cells. Nuclei (karyoplasts) obtained by cytochalasin B treatment of cells contain more than 90 percent of the HMG 1, while enucleated cytoplasts contain the remainder. A similar distribution between karyoplasts and cytoplasts is observed for the H1 histones and the nucleosomal core histones as anticipated. The presence of these proteins, in low amounts, in the cytoplast preparation can be accounted for by the small percentage of unenucleated cells present. In contrast, the nuclei isolated from mechanically disrupted cells contain only 30-40 percent of the total HMGs 1 and 2, the remainder being recovered in the cytosol fraction. No histone is observed in the cytosol fraction. Unike the higher molecular weight HMGs, most of the HMGs 14 and 17 sediment with the nuclei after cell lysis by mechanical disruption. The distribution of HMGs is unaffected by incubating cells with cytochalasin B and mechanically fractionating rather than enucleating them. Therefore, the dramatic difference in HMG 1 distribution observed using the two fractionation techniques cannot be explained by a cytochalasin-B-induced redistribution. On reextraction and sedimentation of isolated nuclei obtained by mechanical cell disruption, only 8 percent of the HMG 1 is released to the supernate. Thus, the majority of the HMG 1 originally isolated with these nuclei, representing 35 percent of the total HMG 1, is stably bound, as is all the HMGs 14 and 17. The remaining 65 percent of the HMGs 1 and 2 is unstably bound and leaks to the cytosol fraction under the conditions of mechanical disruption. It is suggested that the unstably bound HMGs form a protein pool capable of equilibrating between cytoplasm and stably bound HMGs.     

Molecular evolution of rodent insulins

Several trees of amino acid sequences of rodent insulins were derived with the maximum-parsimony procedure. Possible orthologous and paralogous relationships were investigated. Except for a recent gene duplication in the ancestor of rat and mouse, there are no strong arguments for other paralogous relationships. Therefore, a tree in agreement with other biological data is the most reasonable one. According to this tree, the capacity to form zinc-binding hexamers was lost once in the ancestor of the hystricomorph rodents, followed by moderately increased evolutionary rates in the lineages to African porcupine and chinchilla but highly increased rates in at least three independent lines to other taxa of this suborder: guinea pig, cuis, and Octodontoidea (coypu and casiragua).