The biological activity of catfish pancreatic somatostatin

Catfish pancreatic somatostatin, which contains eight additional amino acids on the amino terminus of a tetradecapeptide with considerable homology to tetradecapeptide somatostatin (SRIF), is a naturally occurring homology of the hypothalamic peptide. The purpose of these studies was to determibe the biological activity of this somatostatin homolog. Inhibition of ¹²⁵I-labelled tyr¹-SRIF binding to bovine pituitart plasma membranes by catfish pancreatic somatostatin was approximately 33% that of SRIF. Pancreatic somatostatin has full biological activity measured by inhibition of growth hormone release from isolated rat pituitary cells, but 0.01–0.1% the potency of SRIF. Pancreatic somatostatin at 100 ng/ml produced a 50–60% inhibition of insulin and glucagon secretion from perfused rat pancreas, while SRIF produced comparable inhibition at 10 ng/ml. This report demonstrates that a larger molecular form and natural homolog of SRIF, isolated from fish pancreas, has the same (but reduced) biological activities in rat assay systems as somatostatin originally isolated from sheep hypothalamus.     

Substrate effects in tower loop reactors

Summary Hansenula polymorpha was cultivated in a bubble column loop bioreactor employing ethanol and/or glucose as substrates. By varying the substrate concentration, the cultivations were carried out in non-limited, substrate limited and oxygen transfer limited growth ranges. The influence of the transitions from one range to another on reactor performance (OTR,k _L a, a) and cell productivity () were investigated. When employing ethanol as a substrate, the concentration considerably influences the fluid dynamics, mass transfer phenomena and cell productivity. When employing glucose as a substrate, glucose repression occurs. At high glucose concentrations no transition into the oxygen transfer limited growth is possible. The ethanol produced during the glucose repression influences the fluid dynamics, mass transfer phenomena and productivity. With decreasing glucose concentration the glucose repression can be gradually eliminated.     

Foam behaviour of biological media

Summary A simple method was developed for evaluating foam stability. The influence of KCl and MgSO₄ on foam stability of bovine serum albumin foams was investigated. These salts increase foaminess, but diminish foam stability by the same degree. Thus there is little overall.     

Role of S-adenosylhomocysteine hydrolase in adenosine metabolism in mammalian heart.

S-Adenosylhomocysteine hydrolase of mammalian hearts from different species is exclusively a cytosolic enzyme. The apparent Km for the guinea-pig enzyme was 2.9 microM (synthesis) and 0.39 microM (hydrolysis). Perfusion of isolated guinea-pig hearts for 120 min with L-homocysteine thiolactone (0.23 mM) and adenosine (0.1 mM), in the presence of erythro-9-(2-hydroxynon-3-yl)adenine to inhibit adenosine deaminase, caused tissue contents of S-adenosylhomocysteine to increase from 3.5 to 3600 nmol/g. When endogenous adenosine production was accelerated by perfusion of hearts with hypoxic medium (30% O2), L-homocysteine thiolactone (0.23 mM) increased S-adenosyl-homocysteine 17-fold to 64.3 nmol/g within 15 min. In the presence of 4-nitro-benzylthioinosine (5 microM), an inhibitor of adenosine transport, S-adenosylhomocysteine further increased to 150 nmol/g. L-Homocysteine thiolactone decreased the hypoxia-induced augmentation of adenosine, inosine and hypoxanthine in the tissue and the release of these purines into the coronary system by more than 50%. Our findings indicate that L-homocysteine can profoundly alter adenosine metabolism in the intact heart by conversion of adenosine into S-adenosylhomocysteine. Adenosine formed during hypoxia was most probably generated within the myocardial cell.     

Thiopyronine sensitized photodynamic effect on ribosome synthesis and ribosome content in saccharomyces cells

Summary The content and the synthesis of membrane bound and free ribosomes in growing yeast cells was investigated after photodynamic treatment of the cells with thiopyronine and visible light. It was shown that the synthesis of ribosomes is inhibited after photodynamic treatment and that as a consequence, the content of ribosomes in the cell is diminished.     

The parasitoid complex of three noctuids [Lep.] in a northern Florida cropping system: Seasonal occurrence,parasitization, alternate hosts,and influence of host-habitat

Parasitoids of the cabbage looper,Trichoplusia ni (Hübner), the soybean looper,Pseudoplusia includens (Walker), and the tobacco budworm,Heliothis virescens (F.) were characterized in a 3.2-ha model of a north Florida (U.S.A.) cropping system (including tobacco (Nicotiana tabacum L.), soybeans (Glycine max (L.)Merr. and 18 other crops) not treated with chemical pesticides. The study was for a 2 yr-period; a minimum of three 0.0004-ha sections of row, or 0.0001-ha sections in broadcast or drilled crops were sampled weekly. In addition, sweeps with a net and some other sampling techniques were used in some crops.Litomastix truncatella (Dalman),Meteorus autographae Muesebeck, andVoria ruralis Fallen were the most important larval parasitoids recovered from cabbage loopers;Trichogramma spp. were by far the major egg parasitoid. Parasitization of eggs and larvae in crucifers (Brassica oleracea L.) ranged from 0 to 55% and 0 to 100%, respectively, and was generally highest during the spring and fall. Parasitization of cabbage looper immatures was highest in tomatoes (Lycopersicon esculentum Mill.). Parasitism by the parasitoid complex for the soybean looper larvae was high but eggs in soybeans were seldomly attacked by parasitoids. Tobacco budworm eggs were rarely parasitized in tobacco but were frequently parasitized in tomatoes and okra (Abelmoschus esculentus (L.)Medik). Parasitization of tobacco budworm larvae in tobacco was usually over 50% and was mostly byCardiochiles nigriceps Viereck; fewC. nigriceps were found from the other plants.     

Properties of soluble somatostatin-binding protein

A soluble somatostatin-binding protein was detected in the cytosol fractions of various rat, human and bovine tissues. Maximum binding occurred at pH8.0-8.5 and was Ca(2+)-dependent. The specific binding of somatostatin per 10mug of cytosol protein from 12 rat tissues ranged between 36 and 15%, and 3% for peripheral blood cells. There was also substantial binding in cytosol from human anterior pituitary and liver, and bovine anterior pituitary. The specific binding in rat and human plasma in the presence of EDTA was only 1%. Gel filtration suggested a molecular weight of approx. 80000 for the somatostatin-binding protein from several sources. Exposure of the binding protein to trypsin eliminates somatostatin-binding activity but ribonuclease and deoxyribonuclease have no effect. The binding protein is thermolabile, ethanol-precipitable, and not completely specific for somatostatin. Bound (125)I-labelled [Tyr(1)]somatostatin is not easily displaced by excess of unlabelled somatostatin. The effects of dithiothreitol and mercaptoethanol on the binding of (125)I-labelled [Tyr(1)]somatostatin to the binding protein suggests that binding involves two sequential steps, first loose binding, then disulphide linkage. Since semipurified somatostatin-binding protein causes a dose-related inhibition of the binding of (125)I-labelled [Tyr(1)]somatostatin in radioimmunoassays for somatostatin, estimates of somatostatin content of tissue extracts by radioimmunoassay in some cases may be spuriously high. It is not yet clear whether the binding protein is a true cytosol protein or an easily solubilized membrane protein.