Chymotryptic heavy meromyosin from gizzard myosin: a proteolytic fragment with the regulatory properties of the intact myosin.

Arginine deiminase (EC 3.5.3.6) from $\text{Mycoplasma}\text{arthritidis}$ is a dimeric enzyme. Velocity centrifugation in 6 M guanidine HCl and peptide mapping of the BrCN fragments suggest that the subunits are identical. The reaction of one out of four sulfhydryl groups with 0.3 mM 5,5′-dithiobis-(2-nitrobenzoic acid) has a half-life of about 30 min in 2 M guanidine HCl at 15°, pH 8. The enzyme is irreversibly inhibited by 1 mM formamidinium ion within 1 min. Inactivation by this affinity label is resolvable into two concurrent first-order reactions in the presence of guanidinium ion; the fraction of enzyme which reacts at the faster rate is about 50%. These results are interpreted as evidence for two catalytic subunits which differ in conformation.     

Glyceraldehyde-3-phosphate dehydrogenase activity studied under physiological conditions with a linear assay.

An assay method for glyceraldehyde-3-phosphate dehydrogenase in which none of the primary products accumulate and which gives linear kinetics under physiological conditions has been developed. It is based on the use of the 1,3-diphosphoglycerate produced by the enzyme for the formation of NADPH, while the NADH produced is recycled with an auxiliary system. Revised Km values at pH 7.4 for the muscle (rabbit and rat) enzyme are: glyceraldehyde-3-P, 50 μM; NAD, 100 μM; Pi, 10 mM. The rat erythrocyte enzyme gave similar values except for glyceraldehyde-3-P which was 300 μM. Cooperativity for NAD⁺ tends to be positive but is a variable parameter.     

Evidence from ATP synthesis driven by a proton gradient in Methanosarcina barkeri.

Hepatoma Tissue Culture (HTC) cell nuclei were isolated from untreated cells and from cells treated with sodium butyrate to increase the levels of acetylated histone. Nuclei from sodium butyrate treated cells exhibited a dramatic increased rate of digestion with DNase I as compared to control cell nuclei. Micrococcal nuclease showed no preference for chromatin containing hyperacetylated histones.     

Radioimmune assay of tubulin applied to oligomers, synaptic membranes, and plants

A radioimmune assay for microtubule protein, tubulin, is described, in which unknown amounts of native or denatured tubulin can be quantitated by the ability to compete with pure [¹²⁵I]tubulin for rabbit antibodies produced against purified bovine brain tubulin. The assay is used to demonstrate that crude extracts of mouse brain contain negligible amounts of 30–36S tubulin oligomers under conditions where purified tubulin forms substantial amounts of such structures. Also, the particulate fraction of osmotically shocked and sonicated brain synaptosomes contains negligible tubulin antigenic activity. By contrast, soluble extracts of soybean, especially rapidly dividing regions of the plant, were found to contain significant amounts of cross-reacting material, providing further evidence for the conservative evolutionary nature of this ubiquitous and important protein.     

Synthesis of thromboxane B2 in incubates of dog platelet-rich plasma with arachidonic acid and its inhibition by different drugs

Dog platelets in citrated plasma fail to aggregate upon addition of AA, even though, as demonstrated by bioassay procedures and now by the radioimmunoassay, TxA2 is formed as in case of aggregating human platelets. Imidazole inhibited formation of TxB2 and increased the amounts of PGE2 formed, indicating specific inhibition of thromboxane synthetase. Other drugs tested (benzimidazolamine, compound L8027, indomethacin and isoprenaline) inhibited either cyclo-oxygenase alone, or together with thromboxane synthetase.     

Cell surface component(s) involved in rat hepatocyte intercellular adhesion

Aggregation of rat hepatocytes was effectively inhibited by monovalent antibodies (Fab fragments) directed against hepatocyte plasma membranes, but monovalent antibodies against some distinct, known hepatocyte surface antigens had no effect. Surface antigens, which neutralized the Fab inhibiting effect on cell aggregation, could be solubilized from plasma membranes by limited proteolytic digestion. Thus, hepatocyte intercellular adhesion seems to involve specific cell surface components, which may be proteins or protein derivatives.     

Bromoacetylcholine as an affinity label of the acetylcholine receptor from Torpedo californica

Bromoacetyl[methyl-³H]choline is a highly specific label for the reduced acetylcholine binding site on the acetylcholine receptor from $\text{Torpedo californica}$. Only one of two binding sites per receptor monomer is susceptible to labeling. The labeled site is on the α chain of the receptor.     

Protease inhibitors inhibit production of protein I of the outer membrane in Escherichia coli

Effects of protease inhibitors on composition of newly synthesized protein were studied by pulse-labeling E. coli cells with [³H]leucine and analyzing the labeled proteins by sodium dodecylsulfate gel electrophoresis. In addition to tosyl-lysine chloromethylketone that had been studied previously, antipain, leupeptin and diisopropyl fluorophosphate all inhibited production of a major outer membrane protein, protein I. Synthesis of protein I was specifically inhibited by antipain or leupeptin in strain K12, whereas several other proteins were also affected in strain B. Protein synthesis in strain B was generally more sensitive to inhibition by antipain than that in strain K12.     

Schistosoma mansoni: Phospholipid nature of the “agglutinin”

The haemagglutinating activity of the membrane-associated Schistosoma mansoni “agglutinin” is mainly due to acidic phospholipids, particularly phosphatidylinositol and phosphatidylserine. The role of these phospholipids in possible lipid-protein interactions in the host-parasite relationship is discussed.