Characteristics of newt breeding sites

Breeding site characteristics have been studied for the three species of newt that occur in Britain, the Palmate ( Triturus helveticus (Razoumowski)), Smooth ( T. vulgaris (L.)) and Warty ( T. cristatus (Laurenti)). The Warty newt was seldom found in the absence of the much commoner Smooth newt, but seemed to prefer sites that were relatively large and deep and that had a high proportion of open water surface. All three species tended to breed in ponds having abundant aquatic vegetation. Smooth newts, unlike Palmate newts, were rarely encountered in water with pH <6. The Smooth newt tended to be found in water with relatively high concentrations of metals, while the reverse was true for the Palmate newt. Over Britain, Smooth and Warty newts are relatively less common in soft water areas, while the Palmate is less common in hard water areas. Possible reasons for these associations are discussed.     

Site-directed mutagenesis to determine essential residues of ribulose-bisphosphate carboxylase ofRhodospirillum rubrum

Both Lys-166 and His-291 of ribulosebisphosphate carboxylase/oxygenase fromRhodospirillum rubrum have been implicated as the active-site residue that initiates catalysis. To decide between these two candidates, we resorted to site-directed mutagenesis to replace Lys-166 and His-291 with several amino acids. All 7 of the position-166 mutants tested are severely deficient in carboxylase activity, whereas the alanine and serine mutants at position 291 are ∼40% and ∼18% as active as the native carboxylase, essentially ruling out His-291 in theRhodospirillum rubrum carboxylase (and by inference His-298 in the spinach enzyme) as a catalytically essential residue. The ability of some of the mutant proteins to undergo carbamate formation or to bind either ribulosebisphosphate or a transition-state analogue remains largely unimpaired. This implies that Lys-166 is not required for substrate binding; rather, the results corroborate the earlier postulate that Lys-166 functions as an acid-base group in catalysis or in stabilizing a transition state in the reaction pathway.     

Similarities and differences in phorbol ester- and luteinizing-hormone-induced desensitization of rat tumour Leydig-cell adenylate cyclase.

The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) was shown to mimic luteinizing hormone (LH; lutropin) in causing desensitization of LH-mediated cyclic AMP production in tumour Leydig cells. However, there were differences between LH- and TPA-induced desensitization: (1) TPA induced a more rapid effect than LH; (2) adenosine did not inhibit TPA-induced desensitization, whereas it completely inhibited the LH-induced desensitization; (3) adenylate cyclase activity in plasma membranes from TPA-desensitized cells was not decreased, whereas similar preparations from LH-desensitized cells lost their response to LH and to LH plus guanosine 5'-[beta gamma-imido]triphosphate; TPA-, but not LH-, treated cells had a decreased capacity to respond to cholera toxin and forskolin. These results indicate that LH and phorbol esters induce desensitization of adenylate cyclase in rat tumour Leydig cells by different mechanisms.     

Structural consequences of heme isomerism in monomeric hemoglobins from Glycera dibranchiata

Two-dimensional 1H-NMR methods have been used to assign heme and amino acid proton resonances in both isomeric states of the carbon monoxide complexes of two Glycera dibranchiata monomeric hemoglobins, HbA and HbB. For each hemoglobin, there are small differences in heme pocket structure in the two isomeric forms. The largest structural perturbations associated with heme isomerism involve residues close to pyrrole rings I and II. The positions relative to the heme of phenylalanine CD1 and the proximal histidine ligand are almost unaffected by heme isomerism. These residues probably play a key role in determining the location of the heme within the heme pocket.     

Compatability of Metarhizium anisopliae var. anisopliae with chemical pesticides

The effects of various insecticides on the mycelial growth, sporulation and conidial germination of Metarhizium anisopliae var. anisopliae isolate E₉ were studied in the laboratory. Chlorpyrifos was the most toxic organophosphate to mycelial growth and sporulation at all concentrations. Temephos, malathion and leptophos were highly toxic to sporulation while malathion was the most inhibitory to germination. The carbamates, carbofuran, methomyl and oxamyl were moderately toxic to mycelial growth and sporulation while oxamyl had an adverse effect on germination. The pyrethroids (pyrethrin, permethrin and resmethrin) and the insect growth regulators (diflubenzuron and methoprene) were not inhibitory to the various developmental stages of isolate E₉. The chlorinated hydrocarbons (chlordane, lindane and toxaphene) were more deleterious than all other insecticide groups tested. Among the fungicides, benomyl and maneb produced the greatest inhibition.     

ReducedS-adenosylmethionine: Protein-lysineN-methyltransferase activity (protein methylase III) in shiverer mutant mouse brain

Mice with the dysmyelinating mutation shiverer were studied by measuring the activity of two protein methylases and myelin marker enzymes in the brain. It was observed thatS-adenosylmethionine: protein-lysineN-methyltransferase (protein methylase III, EC. 2.1.1.43) activity is significantly reduced in phenotypically affected homozygous shiverer (shi/shi) mutant mouse brain compared to the unaffected heterozygous littermate brain. This reduction in enzyme activity is manifested mainly by reduced formation of trimethyllysine during the in vitro methylation of histone. In contrast, myelin marker enzymes such as 2,3-cyclic nucleotide 3-phosphohydrolase and 5-nucleotidase as well asS-adenosyl-methionine: protein-carboxylO-methyltransferase (protein methylase II, EC. 2.1.1.24) activities were not significantly affected in these strains of mice.