The haem-enviroment in horseradish peroxidase as seen by proton magnetic relaxation.

The water-proton fast exchange between the vicinity of the ferric haemiron and bulk solvent in horseradish peroxidase solutions at neutral pH has been directly verified by measuring the proton magnetic relaxation times of the aliphatic protons from ethanediol in an otherwise deuterated solution. The implications of this finding are discussed with regard to the stereochemistry of the haem-surrounding.     

Ethnic populations of India as seen from an evolutionary perspective

It is now widely accepted that (i) modern humans,Homo sapiens sapiens, evolved in Africa, (ii) migrated out of Africa and replaced archaic humans in other parts of the world, and (iii) one of the first waves of out-of-Africa migration came into India. India, therefore, served as a major corridor for dispersal of modern humans. By studying variation at DNA level in contemporary human populations of India, we have provided evidence that mitochondrial DNA haplotypes based on RFLPs are strikingly similar across ethnic groups of India, consistent with the hypothesis that a small number of females entered India during the initial process of the peopling of India. We have also provided evidence that there may have been dispersal of humans from India to southeast Asia. In conjunction with haplotype data, nucleotide sequence data of a hypervariable segment (HVS-1) of the mitochondrial genome indicate that the ancestors of the present austro-asiatic tribal populations may have been the most ancient inhabitants of India. Based on Y-chromosomal RFLP and STRP data, we have also been able to trace footprints of human movements from west and central Asia into India.     

Histone-histone proximity in chromatin as seen by imidoester cross-linking

After treatment of purified chromatin with dimethyl adipimidate (a reversible crosslinking reagent) a number of histone oligomers could be isolated in the soluble form from the chromatin. It was shown that all five histones take part in the dimethyl adipimidate-induced oligomer formation. Only a few kinds of histone oligomers (with unknown composition) could be isolated in the soluble form after treatment of chromatic with formaldehyde.     

Water near lipid membranes as seen by infrared spectroscopy

The ordering and H-bonding characteristics of the hydration water of the lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) were studied using polarized infrared spectroscopy by varying either the temperature or the relative humidity of the ambient atmosphere of multibilayer samples. The OH-stretching band of lipid-bound water was interpreted by a simplified two-state model of well-structured, low density “network” water and of less-structured dense “multimer” water. The IR-spectroscopic data reflect a rather continuous change of the water properties with increasing distance from the membrane and with changing temperature. Network and multimer water distribute across the whole polar interphase with changing composition and orientation. Upon dehydration the fraction of network water increases from about 30 to 60%, a value which is similar to that in supercooled water at −25°C. The highly ordered gel phase gives rise to an increased fraction of structured network water compared with the liquid crystalline phase. The IR order parameter shows that the water dipoles rearrange from a more parallel towards a more perpendicular orientation with respect to the membrane normal with progressive hydration. Dedicated to Prof. K. Arnold on the occasion of his 65th birthday.     

Co-rebinding in myoglobin as seen by time-resolved X-ray absorption spectroscopy

The dynamics of selected conformational coordinates, key roles in the understanding of the CO-rebinding process, are investigated in horse heart carbonmonoxy myoglobin (MbCO) through time-resolved X-ray absorption spectroscopy. We present here the results obtained at 90 K in the second time scale. The approach of the CO molecule towards the Fe atom in the active site pocket is speculated to act as a natural precursor to the Fe displacement with the consequent undoming of the protein porphyrin plane. The arrangement of the Fe-C-O bonding angle geometry follows and the final MbCO active site configuration is completely reached within 1 min.