The positional and fatty acid selectivities of oat (Avena sativa L.) seed lipase (triacylglycerol hydrolase EC 3.1.1.3) were examined. Pure triacylglycerols were used as substrates. The products of lipolysis were examined by thin‐layer chromatography and gas‐liquid chromatography. Only symmetrical triacylglycerols were used as substrates; thus potential complications arising from stereobias were avoided. Controls were carried out with a lipase specific for primary positions. The lipase from oat seeds catalyzed the hydrolysis of both primary and secondary esters. When the lipase was tested upon mixtures of homoacid triacylglycerols (triacylglycerols composed of the same three fatty acids), the lipase acted most rapidly upon those containing oleate, elaidate, linoleate and linolenate. Strong intermolecular selectivity against homoacid triacylglycerols containing palmitate, petroselinate and stearate was observed. Comparison of assays performed at 26°C with those performed at 45°C showed that selectivity was temperature‐independent. When mixed‐acid triacylglycerols containing both oleate and stearate were treated with lipase, intramolecular selectivity was observed, with oleate hydrolysis predominating. From this work and earlier work, it can be concluded that the selectivity exhibited by the oat seed lipase is similar to that of the lipase fromGeotrichum candidum, except that the oat seed lipase attacks elaidate, a fatty acyl group with atrans double bond, whereas theG. candidum lipase strongly discriminates against elaidate.
Calmodulins (CaM) were isolated and characterized from two well-known latex producing plants, Papaver somniferum and Euphorbia lathyris. The molecular weights of both were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be 17,000 comparable to that of bovine brain CaM. Amino acid compositions also compared similarly with those of known CaMs, with regard to the presence of trimethyllysine and the ratio of phenylalanine to tyrosine. The Cornish-Bowden equation (SAn) revealed strong statistical correlations of P. somniferum and E. Iathyris CaM with those of other plants and animals, although their amino acid compositions were not identical. Both plant CaM stimulated CaM dependent cAMP phosphodiesterase: for Papaver somniferum the K. was found to be 1.09 nanomolar and for Euphorbia lathyris, 2.01 nanomolar.
Bovine mammary gland calmodulin, purified by conventional fractionation procedures, was compared with similarly purified bovine brain calmodulin. Affinity chromatography on W-7 agarose of the crude fractions from mammary gland and brain yielded pure proteins containing one trimethyllysine residue per 16,800 daltons with essentially identical amino acid compositions. Kinetic parameters of these two proteins with respect to their ability to activate phosphodiesterase were determined. The constants for half maximum activation were .39 and .44 nM for bovine brain and bovine mammary gland calmodulins, respectively; both proteins gave similar maximum velocities. Based on the amino acid composition and kinetic data, it is concluded that the two proteins are essentially identical.
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