A method for density gradient isoelectric focusing in small scale

Isoelectric focusing of plant cell membranes

An isoelectric focusing method is described that discriminates plant cell organelle populations on the basis of surface charge. The isoelectric points (pI values) of the Golgi apparatus, the mitochondria, and putative plasma membrane from etiolated pea stem cells are reported. The pI of the pea Golgi apparatus is similar to that of the (35)SO(4)-labeled membranes of developing Fucus embryos. The pI of Fucus(35)SO(4)-labeled membranes depends on whether the membranes are being polarly transported to the growing tip or randomly transported to the entire periphery of the zygote. Those subject to polar tip transport have a significantly greater negative surface charge than those being randomly transported. The implication of this result toward an understanding of the localization mechanism is discussed. The method is also capable of subfractionating glucan synthetase II-containing membranes (putative plasma membrane) from peas. The pI of putative plasma membrane from a pea stem homogenate is similar to the pI of the plasma membrane of whole protoplasts of Catharanthus leaf cells. Isoelectric focusing appears to be a useful technique to discriminate membranes and, hence, to provide new information and approaches to study cellular and developmental phenomena.

Purification and properties of carnitine acetyltransferases from bovine spermatozoa and heart

To investigate the physical and kinetic properties of sperm carnitine acetyltransferase, the enzyme was purified from bovine spermatozoa and heart muscle. Carnitine acetyltransferase was purified 580-fold from ejaculated bovine spermatozoa to a specific activity of 85 units/mg protein (95% homogeneity). Sperm carnitine acetyltransferase was characterized as a single polypeptide of Mr 62,000 and pI 8.2. Heart carnitine acetyltransferase was purified 650-fold by the same procedure to a final specific activity of 71 units/mg protein. The kinetic properties of purified bovine sperm carnitine acetyltransferase were consistent with the proposed function of this enzyme in acetylcarnitine pool formation. Product inhibition by either acetyl-L-carnitine or CoASH was not sufficient to predict significant in vivo inhibition of acetyl transfer. At high concentrations of L-carnitine, bovine sperm and heart carnitine acetyltransferases were most active with propionyl- and butyryl-CoA substrates, although octanoyl-, iso-butyryl-, and iso-valeryl-CoA were acceptable substrates. Binding of one substrate was enhanced by the presence of the second substrate. Carnitine analogs that have significance in reproduction, such as phosphorylcholine and taurine, did not inhibit carnitine acetyltransferase. Bovine sperm and heart carnitine acetyltransferases were indistinguishable on the basis of purification behavior, pI, pH optima, kinetic properties, acyl-CoA specificity, and sensitivity to sulfhydryl reagents and divalent cations; thus there was no indication that bovine sperm carnitine acetyltransferase is a sperm-specific isozyme.

Drosophila melanogaster alcohol dehydrogenase: an electrophoretic study of the AdhS, AdhF, and AdhUF alleloenzymes

The nature and the interconversion of the three multiple forms Adh-5, Adh-4, and Adh-3 of the purified alleloenzymes AdhS, AdhF, and AdhUF from the fruitfly Drosophila melanogaster have been examined. The experiments show that these multiple forms differ from those in crude extracts of flies homozygous at the Adh locus. On electrophoresis in a starch gel containing NAD or NADH, of purified AdhS which consists of the three Adh forms S-5, S-4, and S-3, five enzymatically active zones appear. This contrasts with the single active zone that arises with crude extracts. Of the five zones that appear with purified enzyme, S-5 gives rise to one, while the other four zones come from the two minor forms S-4 and S-3. The occurrence of the three multiple forms Adh-5, Adh-4, and Adh-3 for each of the purified alleloenzymes is considered due to Adh-5 and, in the case of Adh-4 and Adh-3, deamidation of Adh-5, with the Adh-3 fraction also containing some reversible modified Adh-5. Of the labile amides, at least one must be located in the coenzyme binding region with deamidation preventing coenzyme binding. Pure NAD does not convert Adh-5 to Adh-3 and Adh-1. To produce conversion, the presence of either acetone or butanone along with NAD is necessary. Increased amounts of either acetone or butanone result in increased conversion. In contrast to this, none of the carbonyl compounds cyclohexanone, (+)-and (-)-verbenone, acetaldehyde, acrolein, or crotonaldehyde produces conversion. The ketone group binds to the alcohol binding site in the enzyme-NAD complex. Conversion is considered due to the ketone group binding to a nucleophilic amino acid residue and forming a bridge to the C-4 of the nicotinamide moiety of NAD.

Characterization of L-CAM, a major cell adhesion molecule from embryonic liver cells

We have developed a method for purifying L-CAM, the cell adhesion molecule from embryonic chicken liver cells, and have compared its properties with those of N-CAM, the neural cell adhesion molecule. L-CAM was released from membranes with trypsin, purified by a series of chemical techniques, and used to generate monoclonal antibodies which allowed the identification of the intact L-CAM molecule from membranes. The monoclonal antibodies were used to isolate trypsin-released L-CAM in a single step by affinity chromatography. Material purified by either technique was predominantly a component of M(r) 81,000 on NaDodSO(4)/polyacrylamide gel electrophoresis with a pI of 4.0-4.5. Rabbit antibodies to this component and to the M(r) 81,000 species that had been further purified on NaDodSO(4)/polyacrylamide gel electrophoresis displayed all of the activities of anti-L-CAM. Some of the trypsin-released L-CAM bound specifically to lentil lectin, suggesting that L-CAM is a glycoprotein. The apparent molecular weight of material having L-CAM antigenic determinants depended upon the procedures used to extract membranes; this appears to account for the various values reported previously in the literature. Both the rabbit serum antibodies and the monoclonal antibodies detected the M(r) 81,000 species on immunoblots of unfractionated trypsin-released material. Immunoblots of whole liver cell membranes with the same antibodies revealed a major M(r) 124,000 component, with minor components of M(r) 94,000 and 81,000. Active L-CAM derivatives released by trypsin in the presence of EGTA were detected as a species of M(r) 40,000. L-CAM derivatives obtained by extraction of membranes with EDTA alone appeared as species of M(r) 53,000, 62,000, and 81,000. The combined results suggest that L-CAM on the cell surface is an acidic glycoprotein of M(r) 124,000. In the presence of calcium, the molecule can be released from membranes by trypsin as a soluble M(r) 81,000 fragment; in the absence of calcium, it is released by either endogenous proteases or by trypsin as a variety of smaller fragments.

A comparison of purified poly(ADP-ribose) polymerases from Ehrlich ascites tumor cells, pig thymus, and HeLa S3 cells

Poly(ADP-ribose) polymerases from Ehrlich ascites tumor cells, pig thymus, and HeLa S3 cells were purified by chromatography on DNA-agarose and Blue Sepharose. A molecular mass of 112000 Da was found for all three polymerases. Fragmentation of polyacrylamide-gel-embedded polymerases with cyanogen bromide, and subsequent analysis of the fragments by polyacrylamide gradient gel electrophoresis, showed great similarities with regard to fragment sizes. The amino acid composition of the pig thymus enzyme was very similar to that of the polymerase from Ehrlich ascites tumor cells, and the terminal amino group appeared to be blocked. The HeLa polymerase electrofocused in two peaks at pH 8.8 and 5.5, while the Ehrlich ascites tumor cells and the pig thymus enzyme focused in single peaks at pH 9.4 and 9.6 respectively. Removal of residual DNA by treatment with hydroxyapatite abolished these differences in apparent isoelectric points; all three polymerases focused at pH 9.8. No important differences were found with regard to the effect of a number of substances on the synthesis of poly(ADP-ribose). Apparent Michaelis constants for NAD of 41 microM, 48 microM, and 34 microM were found for polymerase from Ehrlich ascites tumor cells, pig thymus, and HeLa S3 cells, respectively. All these results indicate that the three polymerases, which represented the major poly(ADP-ribose) polymerase activity in the organisms investigated, are closely related proteins.

Studies on a Ca2+-dependent nucleoside triphosphate pyrophosphohydrolase in rat liver plasma membranes

A membrane-bound Ca2+-dependent nucleoside triphosphate pyrophosphohydrolase was solubilized in deoxycholate, separated from inorganic pyrophosphatase, and partially characterized. The Km for a variety of substrates was determined. At 10(-4) M free Ca2+ (pH 8.0) the Km values for ATP and GTP were 0.32 and 2.2 microM, respectively. With ATP as substrate, Mg2+, Sr2+, and Ba2+ could only replace Ca2+ to a limited degree. Both purine and pyrimidine nucleoside triphosphates were hydrolyzed yielding PPi and mononucleotides and similarly AMP and formed from adenosine-(beta gamma-methylene)triphosphate. UDPglucose was hydrolyzed at the pyrophosphate bond. Tripolyphosphate and phosphoribosyl-1-pyrophosphate (P-rib-PP) were not hydrolyzed. Substrate competition experiments showed that GTP inhibited pyrophosphohydrolysis of ATP competitively. However, UDP glucase and adenosine-(beta gamma-methylene)triphosphate inhibited ATP pyrophosphohydrolysis in a non-linear manner. Adenosine-(beta gamma-methylene)triphosphate inhibited pyrophosphohydrolysis of UDPglucose non-competitively, whereas UDPglucose inhibition of adenosine-(beta gamma-methylene) triphosphate pyrophosphohydr-lysis was competitive. The molecular weight of ATP pyrophosphohydrolase was estimated at 120 000 and the pI at 5.1 Pyrophosphohydrolysis of adenosine-(beta gamma-methylene)triphosphate was studied in a number of rat organs. Nearly all activity could be sedimented at 50 000 X g. Very high activities were found in liver, kidney and small intestine, whereas low activities were found in brain and blood.

Poly(ADP-ribose) polymerase from Ehrlich ascites tumor cells. Properties of the purified polymerase

Poly(ADP-ribose) polymerase from Ehrlich ascites tumor cells, partially purified by chromatography on DNA-agarose, was obtained as a more than 80% homogeneous preparation by isoelectric focusing in a sucrose gradient. The polymerase activity was shown to be associated with the major protein in the preparation. Results obtained by electrophoresis in the presence of sodium dodecyl-sulfate indicated that poly(ADP-ribose) polymerase consists of a polypeptide chain with a molecular weight of 130 000. Ultracentrifugation at non-denaturating conditions indicated that the active enzyme may be an oligomeric form of this polypeptide chain. The isoelectric point of the polymerase was 9.40. The effects of various additions to the assay mixture on the synthesis of poly(ADP-ribose) as well as some kinetic data, are given. It is shown that poly(ADP-ribose) is a highly efficient inhibitor of its own synthesis, and results are presented which suggest that the well-known stimulatory effect of DNA on the synthesis is due to reduction of this inhibitory effect of the product.