A Dictyostelium myosin II lacking a proximal 58-kDa portion of the tail is functional in vitro and in vivo.

We used molecular genetic approaches to delete 521 amino acid residues from the proximal portion of the Dictyostelium myosin II tail. The deletion encompasses approximately 40% of the tail, including the S2-LMM junction, a region that in muscle myosin II has been proposed to be important for contraction. The functions of the mutant myosin II are indistinguishable from the wild-type myosin II in our in vitro assays. It binds to actin in a typical rigor configuration in the absence of ATP and it forms filaments in a normal salt-dependent manner. In an in vitro motility assay, both monomeric and filamentous forms of the mutant myosin II translocate actin filaments at 2.4 microns/s at 30 degrees C, similar to that of wild-type myosin II. The mutant myosin II is also functional in vivo. Cells expressing the mutant myosin II in place of the native myosin II perform myosin II-dependent activities such as cytokinesis and formation of fruiting bodies, albeit inefficiently. Growth of the mutant cells in suspension gives rise to many large multinucleated cells, demonstrating that cytokinesis often fails. The majority of the fruiting bodies are also morphologically abnormal. These results demonstrate that this region of the myosin II tail is not required for motile activities but its presence is necessary for optimum function in vivo.     

Determination of trimethylamine and related aliphatic amines in human urine by head-space gas chromatography

A rapid and simple assay procedure employing head-space gas chromatography has been developed for the routine quantification of volatile methylamines and stable trimethylamine N-oxide present in human urine. This assay will enable the rapid screening of patients and aid the diagnosis of fish odour syndrome.     

Role of tissue hypoxia as the mechanism of lactic acidosis during E. coli endotoxemia.

We compared the hemodynamic and metabolic alterations produced in rabbits by similar decreases in cardiac output created by inflating a balloon placed in the right ventricle (n = 6) with those produced by an intravenous bolus of Escherichia coli lipopolysaccharide (LPS; SEP group; n = 6). We measured O2 consumption (VO2), O2 transport (TO2), and O2 extraction ratio (ERO2) for the whole animal and also for the left hindlimb. Both groups experienced similar decreases in cardiac output, systemic TO2, and VO2 and similar increases in ERO2. For the hindlimb, TO2 was similar, but VO2 and ERO2 were lower for the SEP group 30 min after LPS administration (P less than 0.05); however, this difference disappeared during the remainder of the experiment. Arterial lactate concentration was greater (P less than 0.05) for the SEP group. There were no differences in skeletal muscle PO2, measured with a multiwire surface electrode, or in cardiac and skeletal muscle concentrations of high-energy phosphates. We hypothesize that a direct effect of LPS on cellular metabolism may have resulted in greater arterial lactate concentration for the SEP group.     

Modulation of respiratory responses to carotid sinus nerve stimulation by brain hypoxia.

This study examines the effect of progressive isocapnic CO hypoxemia on respiratory afterdischarge and the phrenic neurogram response to supramaximal carotid sinus nerve (CSN) stimulation. Twelve anesthetized, vagotomized, peripherally chemodenervated, ventilated cats with blood pressure controlled were studied. During isocapnic hypoxemia, the amplitude of the phrenic neurogram was progressively depressed. In contrast, the increase in peak phrenic amplitude produced by CSN stimulation was unchanged, suggesting that the central respiratory response to CSN stimulation is unaffected by progressive hypoxemia. The time constant of respiratory afterdischarge (tau) was calculated from best-fit plots of phrenic amplitude vs. time after cessation of CSN stimulation. Under control conditions the value of tau was 57.7 +/- 3 (SE) s (n = 12). During progressive isocapnic hypoxemia, tau decreased as a linear function of arterial O2 content (CaO2) such that a 40% reduction of CaO2 resulted in a 48% reduction in tau. This reduction of respiratory afterdischarge may contribute to the genesis of periodic breathing during hypoxia.     

Genetic and Molecular Organization of Ribosomal DNA (Rdna) Variants in Wild and Cultivated Barley

Twenty rDNA spacer-length variants (slvs) have been identified in barley. These slvs form a ladder in which each variant (with one exception) differs from its immediate neighbors by a 115-bp subrepeat. The 20 slvs are organized in two families, one forming an eight-step ladder (slvs 100-107) in the nucleolus organizer region (NOR) of chromosome 7 and the other a 12-step ladder (slvs 108a-118) in the NOR of chromosome 6. The eight shorter slvs (100-107) segregate and serve as markers of eight alleles of Mendelian locus Rrn2 and the 12 longer slvs (108a-118) segregate and serve as markers of 12 alleles of Mendelian locus Rrn1. Most barley plants (90%) are homozygous for two alleles, including one from each the 100-107 and the 108a-118 series. Two types of departures from this typical pattern of molecular and genetic organization were identified, one featuring compound alleles marked by two slvs of Rrn1 or of Rrn2, and the other featuring presence in Rrn1 of alleles normally found in Rrn2, and vice versa. The individual and joint effects on adaptedness of the rDNA alleles are discussed. It was concluded that selection acting on specific genotypes plays a major role in molding the strikingly different allelic and genotypic frequency distributions seen in populations of wild and cultivated barley from different ecogeographical regions.     

CD4-like molecules in human sperm

The expression of a molecule recognized by CD4 monoclonal antibodies was investigated on human sperm using immunolabelling, biochemical and immunochemical methods. Flow cytometry detected a significant fluorescence signal. SDS-PAGE analysis and Western blotting identified a molecule of 60 kDa, consistent with a CD4-like structure as confirmed after selective immunoseparation. Additional bands reacting with anti-CD4 were found in sperm extracts (73 kDa) and seminal fluid (90 kDa). These data indicate that sperm express a molecule similar to the receptor for HIV described on mononuclear cells.     

Isolation and characterization of human glucose-6-phosphate isomerase isoforms containing two different size subunits

Previously undetected isoforms of human glucose-6-phosphate isomerase (GPI) have been isolated utilizing substrate-induced elution of the enzyme from spherical cross-linked phosphocellulose as an affinity ligand and subjected to a series of physical and chemical studies. The two major isoforms (1, 48%, pI 9.13; 2, 36%, pI 9.00) are homodimers of subunits of 63.2 kDa (Type-A) and are charge isomers, probably representing deamidation of specific Asn-Gly sequences as in other species. Isoform 3 (13%, pI 8.84) is a heterodimer composed of the Type-A subunit and a previously unreported larger subunit of 69.8 kDa (Type-B). Isoform 4 (3%, pI 8.62) is a BB-homodimer. Structural differences in the two types of subunits are also apparent from CNBr fragmentation patterns. Carbohydrate analyses show that, even though potential N- and O-linked glycosylation sites exist, the isoforms are not due to glycosylation. Recently recognized sequence similarities between GPI and the neurotropic lymphokine, neuroleukin (NLK) suggest that GPI and NLK are either derived from the same gene or represent modifications of the same protein. The possibility of NLK-GPI dimers exists, but the new isoforms identified in this study do not appear to represent hybrids of GPI subunits with mature NLK.     

Differential scanning calorimetry study of mixed-chain phosphatidylcholines with a common molecular weight identical with diheptadecanoylphosphatidylcholine

To examine the thermotropic phase behavior of various mixed-chain phosphatidylcholines in excess water and to compare it with the known behavior of identical-chain phosphatidylcholines, we have carried out high-resolution differential scanning calorimetric (DSC) studies on aqueous dispersions of 10 different mixed-chain phosphatidylcholines. These lipids, C(16):C(18)PC, C(18):C(16)PC, C(15):C(19)PC, C(19):C(15)PC, C(14):C(20)PC, C(20):C(14)PC, C(13):C(21)PC, C(21):C(13)PC, C(12):C(22)PC, and C(22):C(12)PC, have a common molecular weight which is the same as that of C(17):C(17)PC, an identical-chain phosphatidylcholine with a molecular weight of 762.2. When the values of any of the thermodynamic parameters (Tm, delta H, and delta S) of the mixed-chain phosphatidylcholines and C(17):C(17)PC are plotted against the normalized chain-length difference (delta C/CL), a linear function with negative slope is obtained provided that the value of delta C/CL is within the range of 0.09-0.4. The linear relationship suggests that these mixed-chain phospholipids are packed in the gel-state bilayer similar to the bilayer structure of C(17):C(17)PC at T less than Tm; however, the negative slope suggests that the conformational statistics of the hydrocarbon chain and the lateral lipid-lipid interactions of these phosphatidylcholines in the gel-state bilayer are perturbed proportionally by a progressive increase in the chain-length inequivalence between the two acyl chains within each lipid molecule. When the value of delta C/CL for mixed-chain phosphatidylcholines reaches the range of 0.44-0.55, the thermotropic phase behavior deviates markedly from that of less asymmetric phosphatidylcholines, suggesting that these highly asymmetric lipids are packed into mixed interdigitated bilayers at T less than Tm. The heating and cooling pathways of aqueous dispersions prepared from the 10 mixed-chain phospholipids are also discussed.     

The Roberts syndrome

Summary Four siblings with the autosomal recessive Roberts syndrome are reported, and we discuss the phenotypic overlap of this syndrome with other similar radial, aplasia syndromes.     

Liver transplantation in a patient with cholangiocarcinoma and ulcerative colitis.

A 39 year-old patient with cholangiocarcinoma and pre-existing ulcerative colitis was successfully treated by orthotopic liver transplantation. He was given low doses of prednisone and azathioprine and survived for more than 9 months, dying with tumour metastases, thrombosis of the inferior vena cava and an intra-abdominal abscess. At autopsy the homograft showed little evidence of rejection. Preoperatively the patient had septicemia. Removal of his liver was difficult. The discrepancy between donor and recipient in size of blood vessels and the presence of two hepatic arteries in the donor caused problems during the vascular anastomoses. During the operation cardiac arrest occurred. Postoperatively there were several medical and surgical problems, including intraperitoneal and gastrointestinal hemorrhage, paralysis of the right dome of the diaphragm, sinus bradycardia, massive diuresis, peroneal nerve palsy, and one major and three minor episodes of rejection, which were reversed by giving pulse doses of methylprednisolone intravenously.