A simple apparatus and procedure for electrofocusing experiments: pL of lactate dehydrogenase and isocitrate lyase

Purification, and comparison, of two forms of dextransucrase from Streptococcus sanguis

A procedure has been developed whereby native and proteolyzed forms of dextransucrase have been purified; it involves gel filtration, and hydroxylapatite chromatography in the presence of 0.10% sodium dodecyl sulfate. This procedure is highly reproducible, and permits approximately 30% recovery of high purity (94% homogeneous) enzyme as an inactive, SDS complex that can be reactivated by the addition of Triton X-100. The purified enzymes have been compared with regard to amino acid compositions, and isoelectric and catalytic properties. An analysis of the structure of their product D-glucans was also made. Although the structural characteristics of the enzyme forms differ, proteolysis does not cause alterations in their catalytic properties.

T-lymphoblast-specific nucleoside kinase: characterization and comparison with deoxycytidine kinase

The results of Sephadex G-100 gel filtration and sucrose density gradient centrifugation showed that T-lymphoblast-specific nucleoside kinase (TSK) purified from MOLT 4FT cell extract has a molecular weight of 26,500, while deoxycytidine kinase (dCK) 56,000. The pI value of TSK (pH 8.2) is quite different from that of dCK (4.8). TSK phosphorylated deoxycytidine, deoxyadenosine, deoxyguanosine and arabinocytidine, similar to dCK, but the respective kinetic properties were quite different. In the phosphate donor specificity and metal ion requirement, some differences were observed between TSK and dCK. dTTP was a good phosphate donor for dCK but no effect at all as phosphate donor for TSK. dCK was inhibited at very low concentration of dCTP, but TSK at much higher concentration of dCTP.

3':5'-cyclic-nucleotide phosphodiesterase in the bovine pituitary gland

Cyclic-AMP phosphodiesterase activity in the homogenate of the anterior pituitary gland was 2-fold higher than that in the homogenate of the posterior pituitary, whereas cyclic-GMP phosphodiesterase activity was dominant in the posterior homogenate. There were two peaks of cyclic-AMP phosphodiesterase activity with different isoelectric points of 4.3 and 5.2. Fraction I had a molecular weight of 240 000 and a sedimentation coefficient of 6.2 S; fraction II had a molecular weight of 180 000 and a sedimentation coefficient of 3.1 S. Cyclic AMP hydrolytic activity in the supernatant of the posterior lobe corresponded to fraction I in the anterior lobe. Cyclic GMP hydrolytic activity in both the anterior and posterior lobes (activated by Ca2+/calmodulin) had an isoelectric point of 5.2, a molecular weight of 240 000 and a sedimentation coefficient of 6.2 S. Cyclic AMP and GMP hydrolytic activities in both the anterior and posterior lobes appeared in fraction I and did not separate when the preparations were mixed before electric focusing or sucrose density gradient procedures. Cyclic AMP hydrolytic activity in fraction II could be separated from cyclic GMP hydrolytic activity.

Low molecular weight cadmium-and copper-binding proteins from rat kidneys

Three isoforms of rat kidney cadmium- and copper-binding proteins [(Cd, Cu)-BP 1, 2, and 3] were isolated. They contained from 75.0 up to 89.0 μg Cd/mg protein, from 7.5 up to 28.0 μg Cu/mg, and from 1.5 up to 12.0 μg Zn/mg protein. Apparent molecular weights of all three isoforms were of about 10,000. Their amino acid compositions were similar to that of rat metallothionein, with cysteine amounting to 25.8-32.7% of all amino acids.

Multiple thymine dimer excising nuclease activities in extracts of human KB cells

Crude extracts of human KB cells grown in suspension culture contain enzyme activity that catalyzes the preferential excision of thymine-containing pyrimidine dimers from UV-irradiated E. coli DNA specifically incised adjacent to dimer sites. Fractionation of KB cell crude extracts reveals the presence of three such activities with distinct affinities for both DEAE-cellulose and phosphocellulose. One of the activities (activity B) is distinguished by its s 20,w (2.6) and isoelectric point (9.0) from the other two (activities A and C) which have similar s 20,w's (3.0-3.2) and isoelectric points (6.0). All three differ in their extent of stimulation by divalent cation and inhibition by NaCl or a sulfhydryl group inhibitor. These results indicate that multiple 5' leads to 3' dimer excision nuclease activities exist in human cells; however, there is as yet no direct evidence that these enzymes are functional in nucleotide excision repair in vivo.

Regulation of protein synthesis in rabbit reticulocyte lysates: purification and initial characterization of the cyclic 3':5'-AMP independent protein kinase of the heme-regulated translational inhibitor

The heme-regulated translational inhibitor (HRI) has been purified 4800-fold. On electrophoresis in sodium dodecyl sulfate/polyacrylamide gel, the purified HRI showed one major polypeptide band. The purified HRI inhibits protein synthesis in lysates containing optimal levels of hemin with inhibition kinetics which parallel those observed in heme-deficiency. Data are presented which are consistent with an enzymatic function of HRI in the inhibition of protein synthesis. The HRI is an adenosine 3':5'-cyclic monophosphate independent protein kinase which phosphorylates the small subunit (38,000) but not the large subunits (52,000 and 50,000) of the initiation factor which forms a ternary complex with Met-tRNAf and GTP. This evidence supports the hypothesis that inhibition of protein synthesis by HRI involves the phosphorylation of the initiation factor. These findings are discussed in relation to various models for the regulation of protein kinase activity by heme. (see article).

Structual comparison of ectopic and normal placental alkaline phosphatase

An alkaline phosphatase immunochemically similar to placental alkaline phosphatase (EC 3.1.3.1) was purified from liver metastases of a giant-cell carcinoma of the lung. Some properties of its physical and chemical structure were determined and compared to those of purified placental alkaline phosphatase. The purified tumor phosphatase and the placental phosphatase were similar with regard to the following properties: (1) NH(2)-terminal sequence, (2) peptide map, (3) subunit molecular weight, and (4) isoelectric point. The physical properties and NH(2)-terminal sequence of alkaline phosphatase isoenzyme of liver differed from the placental and the tumor enzyme. The data from the present study strongly support the hypothesis that the tumor and the placental alkaline phosphatases are products of the same gene.

Newer techniques in protein isolation and characterization

This review summarizes theory, experimental procedures and applications of current research methodology in each stage of protein purification from the disruption of seed structures and isolation of protein bodies to cleavage of intermolecular bonds and the purification of individual proteins. Methods for characterizing proteins are discussed in terms of their utility in monitoring protein isolations, disclosing structural features and predicting protein behavior. Specific topics include: the macrostructure of seeds, scanning electron microscopy, particle fractionation by density gradient centrifugation, filtration, association‐dissociation of seed proteins, disulfide bonds and other forms of intermolecular bonding, high pressure gel filtration, immunospecific adsorbents or precipitating agents, immunochemical techniques, isoelectric focusing, physical and chemical methods for characterizing proteins, differential thermal analysis and the determination of polypeptide sequences.

Isoelectric focusing of human liver alkaline phosphatase

1. Isoelectric focusing of human liver alkaline phosphatase in a sucrose density gradient with LKB Ampholine as carrier ampholytes is described. 2. Problems due to the chelating properties of the ampholytes and the pH gradient were examined. 3. A reactivation procedure to counter these effects was devised that can probably be used for other alkaline phosphatases. 4. The isoelectric point of human liver alkaline phosphatase was found to be pH3.9.