Effect of lipid composition on the calcium/adenosine 5'-triphosphate coupling ratio of the Ca2+-ATPase of sarcoplasmic reticulum

The Ca2+-ATPase of sarcoplasmic reticulum was purified and depleted of proteolipids by solubilization in Triton X-100 and by fractionation on a DE-52 column. The protein reconstituted by deoxycholate-cholate dialysis at low lipid to protein ratios (2-5 mg of lipid/mg of protein), with either dioleoylphosphatidylethanolamine or monogalactosyldiglyceride, exhibited high initial rates of ATP-dependent Ca2+ uptake [300-900 nmol min-1 (mg of protein)-1] and coupling ratios (Ca2+ transported/ATP hydrolyzed) up to 1.2. Ca2+-ATPase reconstituted with lipids of increasing degrees of methylation (dioleoylphosphatidylethanolamine, dioleoylmonomethylphosphatidylethanolamine, dioleoyldimethylphosphatidylethanolamine and dioleoylphosphatidylcholine) or increasing degrees of glycosylation (monogalactosyldiglyceride and digalactosyldiglyceride) revealed a progressive decrease in both ATP-dependent Ca2+-uptake and coupling ratios. The rate and extent of Ca2+ uptake decreased as the dioleoylphosphatidylethanolamine/dioleoylphosphatidylcholine or monogalactosyldiglyceride/dioleoylphosphatidylcholine molar ratios in the reconstituted vesicles were reduced. Vesicles reconstituted with high molar ratios of dioleoylphosphatidylethanolamine/dioleoylphosphatidylcholine or monogalactosyldiglyceride/dioleoylphosphatidylcholine and at a high lipid to protein ratio became leaky and released the Ca2+ accumulated inside the vesicles when the temperature of the incubation mixture was increased (e.g., from 20 to 37 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)     

Production of pectinases byAspergillus sp using differently pretreated lemon peel as the carbon source

Summary Aspergillus sp strains from decaying lemons were tested for extracellular pectinase production, testing differently pretreated lemon peel as the carbon source instead of pectin. It was found that the production of extracellular polygalacturonase was about the same and that of pectinesterase substantially higher when unwashed fresh lemon peel was used instead of pectin. The culture filtrate obtained showed a clarifying capacity similar to that of a commercial pectinase preparation, but the vitamin C of the juice was less affected by the treatment.     

A new synaptic anomaly: irregular synaptonemal complexes

Summary In this paper we describe a new synaptic anomaly characterized by the presence of irregular synaptonemal complexes (SCs) in two sterile patients.     

Increased GH responsiveness to dopamine receptor stimulation in alcohol addicts during the late withdrawal syndrome

In humans the release of growth hormone (GH) elicited by dopamine (DA) and DA agonists may represent a reliable model to assess change in sensitivity of DA receptors. We now report that in chronic alcoholics, 4–7 days after the suspension of alcohol consumption, the increase of GH response to DA infusion was higher than that seen in non alcoholic volunteers. The specificity of this GH response to DA administration was demonstrated by the use of domperidone, a novel peripheral antagonist of DA receptors. These results suggest the development of hyper-responsiveness of DA receptors involved in the control of GH secretion in chronic alcoholics during the later phases of the “withdrawal syndrome”.     

The steroids and fatty acids of the basidiomycete Scleroderma polyrhizum

The fruit bodies of the Basidiomycete Scleroderma polyrhizum have been shown to contain the steroids ergosta-4,6,8(14) 22-tetraen-3-one and 5α,8α-epidoxyergosta-6,22-dien-3β-ol and also palmitic and oleic acids.     

Acid phosphatase from maize scutellum: Negative cooperativity suppression by glucose

Acid phosphatase purified from maize scutellum, upon acylation with succinic anhydride, still shows negative co-operativity for the hydrolysis of glucose-6-phosphate at pH 5.4. This phenomenon is abolished by glucose, for both native and succinylated enzymes, through stimulation of the initial velocities at sub-optimal substrate concentrations. However, negative co-operativity for the enzymatic hydrolysis of p-nitrophenylphosphate at pH 5.4 is suppressed only at high concentrations of glucose. Furthermore, the hydrolysis of p-nitrophenylphosphate is noncompetitively inhibited (low affinity form of the enzyme molecule) by glucose, which suggests the existence of different substrate binding sites.     

Esterase-type of activity possessed by human plasma apolipoprotein C-II and its synthetic fragments

Human plasma apolipoproteins apoA-I, A-II, C-I, C-II and C-III (with the exception of apoE), porcine pancreatic colipase and procolipase hydrolyze 4-methylumbelliferyloleate. In all cases, liberation of 4-methylumbelliferone could be inhibited by phenylmethylsulfonylfluoride, thus suggesting the involvement of serine residues. To the best of our knowledge this is the first report on the esterase activities of these peptides. Synthetic fragments of the lipoprotein lipase activator, apoC-II, prepared according to the known sequence, also possessed this esterase-type of activity. Furthermore, the esterase-type of activities of the synthetic apoC-II fragments with different chain lengths bore a relatively good correlation to the reported abilities to these peptides to produce activation of lipoprotein lipase.We propose a model for the mechanism of activation of lipoprotein lipase by apolipoprotein C-II. ApoC-II would enhance the apparent catalytic rate constant of lipoprotein lipase by functioning as a specific acyl-enzyme hydrolase. A similar catalytic mechanism is suggested for other protein co-factors of hydrolytic enzymes.     

Acid hydrolases in the perinuclear secretion granules of the rat preputial gland. A light and electron microscope study

Synopsis Four acid hydrolases in the secretory cells and the sebum of the preputial sebaceous gland of the rat were incestigated cytochemically. A strong -glucuronidase activity was found to occur in the matrix of the perinuclear secretion granules, whereas the granule crystalloids were unreactive. The distribution of acid phosphatase at the light microscope level was similar, though the intensity of the reaction was lower and the number of positive granules smaller. By electron microscopy, the final reaction product of acid phosphatase occurred in patches at the periphery of the granule matrix, as well as in the vesicles adjoining the Golgi stacks, from which the perinuclear granules seemed to arise. In the sebum, the two hydrolases occurred in the background material between the unstained crystalloid masses. There was noN-acetyl--glucosaminidase or aryl sulphatase activity in the gland. The perinuclear granules appear to be secretory lysosomes which, after discharge from the disaggregating cell, release their acid hydrolases into the sebum.     

Pyridoxal phosphate-sensitized photoinactivation of glutamate decarboxylase from Clostridium perfringens

1. l-Glutamate decarboxylase (EC 4.1.1.15) from Clostridium perfringens was inactivated by exposure to visible light at pH6.2. 2. Inactivation does not occur at pH4.6 or in the absence of bound pyridoxal phosphate. 3. On prolonged photo-oxidation six histidine residues per molecule of enzyme were destroyed. 4. The loss of six cysteine residues per molecule occurred both in irradiated samples and in controls oxygenated in the dark. 5. This dark-oxidation of cysteine residues is apparently required before the photo-oxidation process. 6. The absorbance, fluorescence and circular-dichroism properties of the enzyme as well as its elution volume during Sephadex gel-filtration were unaffected by prolonged irradiation. 7. However, an apparently homogeneous product of photo-oxidation could be separated from the control enzyme by ion-exchange chromatography. 8. The K(m) for l-glutamate was unchanged in an irradiated sample retaining 22% of control activity. 9. These data and the catalytic role of imidazole residues at the active sites of amino acid decarboxylases are discussed.