Direct addition of insulin inhibits a high affinity Ca2+-ATPase in isolated adipocyte plasma membranes.

The mechanism by which insulin regulates cellular metabolism remains unknown although indirect evidence suggests that alterations in intracellular calcium are important. More specifically, it has been proposed that insulin triggers an increase in intracellular calcium which is responsible for the subsequent modification of metabolic activities. The cell maintains a large electrochemical gradient for ionised calcium between the cytoplasm (less than 10(-6) M, as determined for muscle and nerve) and the extracellular environment (less than 10(-3) M). The plasma membrane may, therefore, be important in the regulation of calcium homeostasis, as a slight alteration in the processes maintaining this gradient could result in marked changes in cytoplasmic calcium. One such process is the active extrusion of calcium from the cell by a high affinity calcium-stimulated ATPase (Ca2+-ATPase). Such a mechanism has been well established in red cells and is postulated in nerve, liver and muscle. We have identified a high affinity Ca2+-ATPase in a plasma membrane-enriched subcellular fraction isolated from rat adipocytes which may provide the enzymatic basis for a calcium extrusion pump. We demonstrate here that the Ca2+-ATPase is specifically inhibited by the direct addition of physiological concentrations of insulin to the direct addition of physiological concentrations of insulin to the isolated plasma membranes. This effect suggests that direct regulation of calcium homeostasis may represent an important event in the mechanism of action of insulin.     

Endogenous mammary tumour virus DNA varies among wild mice and segregates during inbreeding.

Proviruses of the mouse mammary tumour virus (MMTV) endogenous to normal mice can be identified by molecular hybridisation and distinguished using restriction endonucleases. Feral mice display marked heterogeneity with respect to the number of copies and the sites of insertion of endogenous MMTV-specific DNA, with occasional mice apparently free of MMTV DNA. Several different MMTV proviruses present in laboratory mice have segregated like stable, independent genetic elements during the inbreeding which followed a cross between Bagg albino and DBA mice 60 years ago. The results favour the hypothesis that endogenous proviruses have been established by multiple, independent infections of germ cells rather than by somatic mutation of ancestral proviruses or of cellular genes.     

Three new types of viral oncogene of cellular origin specific for haematopoietic cell transformation.

The RNAs of seven replication-defective leukaemia virus (DLV) strains contain three types of unique sequences, which correlate with the capacity of a given virus strain to transform erythroblasts, macrophage-like cells and myeloblasts, respectively. These sequences, termed erb, mac and myb, have their counterparts in the normal DNA of avian and mammalian species. Our results indicate that DLVs represent recombinants between a common 'vector' related to a chicken endogenous virus and one of three types of cellular gene possibly involved in haematopoietic differentiation.     

A structurally abnormal insulin causing human diabetes.

Insulin isolated from the pancreas of a diabetic patient with fasting hyperinsulinaemia showed decreased activity in binding to cell membrane insulin receptors and in stimulating cellular 2-deoxyglucose transport and glucose oxidation. Chemical studies suggest that the isolated hormone is a mixture of normal insulin and an abnormal variant which contains a leucine for phenylalanine substitution at position 24 or 25 of the insulin B-chain.     

Direct expression in Escherichia coli of a DNA sequence coding for human growth hormone.

DNA coding for human growth hormone was constructed by using chemically synthesised DNA in conjunction with enzymatically prepared cDNA. This 'hybrid' gene was expressed in Escherichia coli under the control of the lac promoter. A polypeptide was produced having the size and immunological properties characteristic of mature human growth hormone.     

Competence for genetic transformation in pneumococcus depends on synthesis of a small set of proteins.

In bacterial genetic transformation the uptake of DNA and its integration into the resident chromosome is dependent on a special cellular state, termed competence. In those species where appearance of competence has been studied, specific (but often poorly defined) growth conditions lead to a simultaneous development of competence in a substantial fraction of the cells in a culture. In Bacillus subtilis, and in Haemophilus species, competence appears in the stationary phase of growth or in certain other growth-limiting conditions. Streptococcus pneumoniae (pneumococcus) is perhaps unusual in that virtually all cells of a culture become competent, for a short period at a specific cell density during logarithmic growth, without perturbing the growth rate. The synchronous appearance of competence in pneumococcal cultures results from an autocatalytic effect of a small protein released by the cells that induces competence. The response to competence factor has been shown to require protein synthesis. We report here additional information on the nature of competence in pneumococcus: pulse-labelling studies show that for the brief period of competence protein synthesis is restricted to a few specific polypeptides.     

Evidence that three structural genes code for human alkaline phosphatases.

The number of structural gene loci that code for the different molecular forms of human alkaline phosphatase is unknown. Physical properties of the enzymes, immunological data, chemical inhibition and genetic studies suggest that at least three structural genes are involved: one coding for alkaline phosphatase from placenta, another for the enzyme from intestine, and one or more for the enzymes from liver, kidney and bone. Badger and Sussman have shown that alkaline phosphatases from human liver and placenta are products of different structural genes, and Greene and Sussman have shown that alkaline phosphatase from a metastasised bronchogenic carcinoma was nearly identical to the enzyme from placenta. However, other tumour-associated alkaline phosphatases and the enzymes from normal tissue other than placenta and liver have not been identified by conclusive structural criteria, and thus it is not known whether these onco-alkaline phosphatases represent ectopic production or unusual post-translational modification of the enzymes found in normal tissues. We present here, using a sensitive peptide-mapping technique, structural evidence that the enzyme forms from liver, kidney and serum from a patient with Paget's disease of bone (osteitis deformans) are products of the same structural gene and can be easily distinguished from either the intestinal or placental isoenzymes. The technqiue seems to be useful for the classification of tumour-associated alkaline phosphatases on a structural basis.     

Evidence for the bilobal nature of diferric rabbit plasma transferrin.

Plasma transferrin is involved in iron transport within the circulatory system of vertebrates, and provides an iron source for haemoglobin synthesis and other metabolic requirements. However, despite extensive studies by spectroscopic, biochemical and physiological techniques, the nature of iron binding and the mechanisms of uptake and release of iron are not fully understood. Plasma transferrins are monomeric glycoproteins with a molecular weight of approximately 80,000 (ref. 2); they have two similar and very strong binding sites for Fe(III), together with two associated anion binding sites. Fragmentation studies on various transferrins have shown that the polypeptide chain is composed of two domains formed from the N-terminal and C-terminal halves of the polypeptide chain. Each domain contains one metal binding site. The marked sequence similarities which exist between the two halves may reflect a doubling of an ancestral structural gene during the phylogenetic development of the protein. Preliminary crystallographic investigations of diferric rabbit plasma transferrin have been reported from this laboratory. We now report initial studies of the X-ray structure determination of dife-ric rabbit plasma transferrin which have led to a 6-A resolution electron density map.     

Bombesin suppresses feeding in rats.

Bombesin (BBS) is a tetradecapeptide originally isolated from amphibian skin1. BBS-like immunoactivity is widely distributed in mammalian gut2-5, and plasma levels have been shown to rise sharply following feeding (ref. 6 and V. Erspamer, personal communication). The physiological actions of BBS are unknown. We have previously shown that the classic gut hormone cholecystokinin (CCK) is a powerful and specific suppressor of food intake7-9. Although CCK and BBS lack common amino acid sequences, they have certain common actions on gut viscera10,11. We have now shown that BBS also suppresses food intake, and we compare its action with that of CCK.