The essential light chains constitute part of the active site of smooth muscle myosin

Myosin, a major contractile protein, characteristically possesses a long coiled-coil alpha-helical tail and two heads. Each head contains both an actin binding site and an ATPase site and is formed from the NH2-terminal half of one of the two heavy chains (relative molecular mass, Mr, 200,000) and a pair of light chains; the so-called regulatory and essential light chains of approximately Mr 20,000 each. Recently we have identified Trp 130 of the myosin heavy chain from rabbit skeletal muscle as an active-site amino-acid residue after labelling with a new photoaffinity analogue of ADP, N-(4-azido-2-nitrophenyl)-2-aminoethyl diphosphate (NANDP). Nonspecific labelling was eliminated by first trapping NANDP at the active site with thiol crosslinking agents. Exclusive labelling of the heavy chains with no labelling of the light chains agreed with previous findings that the heavy chains alone contain the actin-activated Mg-ATPase activity of rabbit skeletal myosin. Here we report similar photolabelling experiments with smooth muscle myosin (chicken gizzard) in which 3H-NANDP is trapped at the active site with vanadate and which show that both the heavy chains and the essential light chains are labelled. The results indicate that both chains contribute to the ATP binding site and represent the first direct evidence for participation of the essential light chains in the active site of any type of myosin.     

Phorbol ester and diacylglycerol mimic growth factors in raising cytoplasmic pH

There is now good evidence that cytoplasmic pH (pHi) may have an important role in the metabolic activation of quiescent cells. In particular, growth stimulation of mammalian fibroblasts leads to a rapid increase in pHi (refs 3-6), due to activation of a Na+/H+ exchanger in the plasma membrane, and this alkalinization is necessary for the initiation of DNA synthesis. However, the mechanism by which mitogens activate the Na+/H+ exchanger to raise pHi is not known, although an increase in cytoplasmic free Ca2+ ([Ca2+]i) has been postulated as the primary trigger. We now present data suggesting that the Na+/H+ exchanger is set in motion through protein kinase C, a phospholipid- and Ca2+-dependent enzyme normally activated by diacylglycerol produced from inositol phospholipids in response to external stimuli. Using newly developed pH microelectrodes and fluorimetric techniques, we show that a tumour promoting phorbol ester and synthetic diacylglycerol, both potent activators of kinase C (refs 12-15), mimic the action of mitogens in rapidly elevating pHi in different cell types. Furthermore, we demonstrate that, contrary to previous views, an early rise in [Ca2+]i is not essential for the activation of Na+/H+ exchange and the resultant increase in pHi. Finally, we suggest that an alkaline pHi shift, mediated by Na+/H+ exchange, may be a common signal in the action of those hormones which elicit the breakdown of inositol phospholipids.     

Loss of a Harvey ras allele in sporadic Wilms' tumour

Genomic changes within chromosome band 11p13 appear to have a role in the initiation of Wilms' tumour. The human Harvey ras oncogene, c-Ha-ras 1, has been located by Jhanwar et al. immediately adjacent to this region at band 11p14 .1, although several groups have assigned the gene more distally at band 11p15 . We have examined tumour DNA from two cases of sporadic Wilms' tumour, and report here that in both cases one of the two constitutional c-Ha-ras 1 alleles was absent. One tumour had a reciprocal translocation between the short arm of chromosome 11 (at band 11p13), and the long arm of chromosome 12, with no visible loss of chromosomal material. The loss of a c-Ha-ras 1 allele in association with this translocation indicates that a submicroscopic deletion had occurred. The resulting hemizygosity may have had a role in tumour initiation. Our results indicate that the c-Ha-ras 1 gene and the 'Wilms' tumour locus' may be in close proximity. It would, therefore, be premature to exclude the possibility that these two sites are functionally related.     

Plasma catecholamines in children

Summary Plasma catecholamine concentrations in 46 children of various ages were determined by a sensitive radioenzymatic assay. Noradrenaline levels were found to be in the same range as in adults, whereas adrenaline levels in a few of the children were abnormally high.     

Tests of the helix dipole model for stabilization of alpha-helices

Charged groups play a critical role in the stability of the helix formed by the isolated C-peptide (residues 1-13 of ribonuclease A) in aqueous solution. One charged-group effect may arise from interactions between charged residues at either end of the helix and the helix dipole. We report here that studies of C-peptide analogues support the helix dipole model, and provide further evidence for the importance of electrostatic interactions not included in the Zimm-Bragg model for alpha-helix formation.     

Research of Industrial Regions Classification at County-Level

The paper studies some important issues concerning the classification of industrialregions at the county-level by using methods of correlation-principal component analysis and fuzzycluster technique.According to reality it also gives a case study in which the connty-level industrialregional classification is simulated.