The International journal of biochemistry最新文献

1. alpha-Macroglobulins (alpha Ms) were isolated from the serum of injured rats through a two-stage method: gel filtration and ultracentrifugation. 2. The clearance rates of rat plasma kallikrein (RPK) and alpha Ms-RPK complexes were compared in an isolated rat liver perfusion system: the alpha Ms-RPK complexes are cleared at a much slower rate (half-life ranging from 24 to > 120 min) than does RPK itself (half-life ranging from 13 to 18 min).

1. Numerous studies have demonstrated the presence of at least four glycolytic enzymes in the nuclear compartment of several cell systems. 2. These include, lactate dehydrogenase, phosphoglycerate kinase, aldolase and glyceraldehyde-3-phosphate dehydrogenase. 3. In some cases the glycolytic enzymes found in the nuclei were a modified form from that found in the cytoplasmic counterpart. 4. In all four cases, the nuclear form of these glycolytic enzymes has been reported to bind DNA. 5. Although none of these enzymes interact with a specific target DNA sequence, their association with DNA may play a role in transcription and replication of DNA through general stabilization of the nuclear matrix or chromatin structure. 6. The present review aims to summarize the current understanding of this phenomenon and to examine the role of the DNA-binding activities of the glycolytic enzymes in cell growth and differentiation.

1. We show here that treatment of diaphragm muscle with 2,4-dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, abolished the stimulatory action of insulin on binding of the glycolytic enzymes, phosphofructokinase (PFK) and aldolase, to muscle cytoskeleton. This effect was demonstrated with low concentration of DNP, which caused only a small decrease in ATP and did not affect the basic levels of cytoskeleton-bound glycolytic enzymes. 2. Higher concentrations of DNP, which induced a drastic decline in ATP content, caused a decrease in cytoskeleton-bound glycolytic enzymes and damage to myofibrils. 3. These results suggest that mitochondrial ATP is required for both the preservation of the basal levels of cytoskeleton-bound glycolytic enzymes and cell structure, as well as for the expression of the stimulatory action of insulin on glycolytic enzymes' binding to muscle cytoskeleton.

1. Both activities of NADH- and NADPH-linked aquacobalamin reductases were found in some human tissues, liver, kidney pancreas, heart, spleen, lung, cerebrum, cerebellum, adrenal glands, stomach, duodenum, jejunum, ileum, colon and bone marrow. 2. Human liver contained both enzymes with higher specific activities than any other tissues. 3. The liver NADH-linked enzyme was distributed in both mitochondrial (approx. 60%) and microsomal (40%) fractions; similar to the distribution of the NADPH-linked enzyme, but of which 40% activity was found in the mitochondria and the remaining activity was recovered in the microsomes. 4. The results suggest that the synthetic systems of the cobalamin coenzymes occur in both mitochondria and microsomes of human liver.

1. Four perchloric acid-soluble fractions (PASFs) from human liver metastases of sigmoid colon carcinoma (LSCC), pancreas carcinoma (LPC), breast carcinoma (LBC) and human normal liver (NL) were subjected to DEAE-cellulose column chromatography and separated into three glycoprotein fractions, respectively. 2. In chromatography, LSCC-PASF and LBC-PASF gave Thomsen-Friedenreich (T)-active glycoprotein, blood group N antigen precursor glycoprotein with T activity and N antigen precursor glycoprotein, respectively. 3. LPC-PASF gave N antigen precursor glycoprotein with T activity and two N antigen precursor glycoproteins. 4. The three glycoprotein fractions from NL-PASF did not exhibit both T activity and N antigen precursor activity.

In regenerating rat liver, an elevated protein kinase activity was detected which phosphorylated ribosomal protein S6 and histones. The properties of this enzyme were closely similar with those of protease-activated protein kinase C with Mr 45,000. During the study of the mechanism of proteolytic activation, type III protein kinase C (encoding alpha-sequence) was shown to be subjected to limited proteolysis by trypsin-like protease and converted to protein kinase M in ionic strength- and pH-dependent manner. This reaction was stimulated in the presence of Ca2+ and phospholipid under slightly higher ionic strength condition than physiological level (greater than 140 mM NaCl) and alkaline pH (7.5-8.0). These results suggest that activation of Na+/H+ exchanger in plasma membrane may trigger this type of proteolytic activation of protein kinase C. In addition to protein kinase M, another type of protease-activated kinase with Mr 80,000 was detected when limited proteolysis of protein kinase C was performed on inactive form of this enzyme (in the absence of either Ca2+ or phospholipid or both activators) under lower ionic strength condition. The molecular mass of this active enzyme was slightly smaller (approximately 200) than that of native protein kinase C. However, it is not clear at this time whether this small fragment was released from amino-terminal or carboxy-terminal domain to make protein kinase C partially active in the absence of Ca2+ and phospholipid. Although it has been proposed that proteolytic degradation of protein kinase C is involved in down regulation of this enzyme, the physiological significance of these two types of protease-activated forms of protein kinases in liver has remained obscure.

1. Murine dihydrofolate reductase was produced efficiently in a Xenopus laevis oocyte that received microinjection of the dihydrofolate reductase mRNA. 2. Murine dihydrofolate reductase was produced under the direction of the plasmid pAdD26SVpA, which contains adenovirus major late promoter and the simian virus 40 T antigen gene for transcription initiation and murine dehydrofolate reductase complementary DNA fragment. 3. Injection of the plasmid pDHFR26, which contains murine dihydrofolate reductase complementary DNA and normal transcription initiation site segment in the 5' untranslational region, failed to produce proper translational products due to improper transcription.

1. A simple method for purifying transferrins and lactoferrin is described. 2. The method consists of a preliminary step of dye-ligand chromatography using DEAE Affi-Gel Blue as the gel matrix at pH 7.5. In this chromatographic step, the transferrins and lactoferrin were readily separated from the bulk of the other proteins by start buffer elution. 3. Differences in the chromatographic behaviour of the various serum transferrins (monkey, human, rabbit, pig, chicken and duck) and ovotransferrin upon DEAE Affi-Gel Blue chromatography can be attributed to differences in the anionic charge of the transferrins in 0.02 M potassium phosphate buffer, pH 7.5, thus resulting in the differential retardation of these protein molecules by the gel matrix. 4. The result of DEAE Affi-Gel Blue chromatography of human lactoferrin is different from that for the transferrins. This may possibly reflect the differences in the strength of interaction between lactoferrin and transferrin with this gel matrix.

1. Activity of a 5'-nucleotidase which preferentially hydrolyses IMP and GMP was determined by immunotitration in various mammalian tissues. 2. Activity per g of rat tissue was high in testis and spleen and low in skeletal muscle. 3. In human cells, the activity was high in fibroblasts and low in erythrocytes.