Developmental profiles and properties of hepatic peroxisomal apo- and mitochondrial holoalanine:glyoxylate aminotransferase during chick embryogenesis

Preparation of "functional" mitochondria: a challenging business

As the powerhouse of the cell, mitochondria play a crucial role in many aspects of life, whereby mitochondrial dysfunctions are associated with pathogenesis of many diseases, like neurodegenerative diseases, obesity, cancer, and metabolic as well as cardiovascular disorders. Mitochondria analysis frequently starts with isolation and enrichment procedures potentially affecting mitochondrial morphology having impact on their function. Due to the complex mitochondrial morphology, the major task is to preserve their structural integrity. Here we critically review a commonly used isolation procedure for mitochondria utilizing differential (gradient) centrifugation and depict major challenges to achieve "functional" mitochondria as basis for comprehensive physiological studies.

A critical comparison between two classical and a kit-based method for mitochondria isolation

Numerous protocols for isolation of mitochondria are available. Here, three methods for the isolation of intact mitochondria from mouse liver tissues are compared with regard to yield, purity and activity. Mitochondria were isolated by sucrose density gradient ultracentrifugation, free-flow electrophoresis or a commercially available kit-based method. Our analyses show that the sophisticated (and most expensive) free-flow electrophoresis method enables isolation of intact mitochondria with an enrichment of approximately 70%. Using the classical density centrifugation method is very laborious and time-consuming, but delivers about 57% intact mitochondria. Using standard laboratory equipment in a quick and simple procedure, the kit provides approximately 50% intact mitochondria, suitable for most standard investigations.

A new type of matrix vesicles is found in fetal bovine tracheal cartilage

Using 4-month-old fetal bovine tissue, the properties of the tibia epiphyseal cartilage matrix vesicles, a type of endochondral ossification tissue, were compared with those from tracheal cartilage. The matrix vesicle fractions, obtained by collagenase digestion and differential centrifugation, were subjected to sucrose-density-gradient centrifugation. Alkaline phosphatase activity, protease activity, and lacatate dehydrogenase activity were assayed for the marker enzyme of the matrix vesicles. Matrix vesicles containing alkaline phosphatase, metalloprotease, and lacatate dehydrogenase were found in the tibia epiphyseal cartilage at a density of 1.11 g/ml. In surprising contrast, we also found matrix vesicle-like vesicles with a high density of 1.24 g/ml in the tracheal cartilage. These also contained alkaline phosphatase and lactate dehydrogenase, but not metalloprotease. The electrophoretic profiles of the lactate dehydrogenase isoenzymes from the matrix vesicle and matrix vesicle-like vesicles were identical with those of chondrocyte cytosolic lactate dehydrogenase. Aldolase, aspartate: 2-oxoglutarate aminotransferase, alanine: 2-oxoglutarate aminotransferase, glucose-6-phosphatase, glutamate dehydrogenase, catalase, and cytosolic enzymes except for lactate dehydrogenase were not detected in these vesicles. These results suggest the presence of a mechanism for specific uptake of cytosolic lactate dehydrogenase in both vesicles. In this study, a new type of matrix vesicles without protease was found in the tracheal cartilage, a kind of permanent cartilage, but not in the tibia epiphyseal cartilage, which is replaced by bone tissue.

The presence of vesicles containing lactate dehydrogenase in the ameloblast layer of bovine enamel organ

Ameloblast layers were removed from bovine enamel organs, followed by the separation of the extracellular matrix-vesicle fraction after collagenase digestion. Lactate dehydrogenase (LDH)-containing vesicles were found in that fraction. LDH in these vesicles did not result from cell lysis and vesicle capture during the preparation of the fraction. The isoenzyme pattern of LDH in LDH-containing vesicles was similar to that of cytosolic LDH of ameloblasts, suggesting the presence of a mechanism for specific uptake of cytosolic LDH during the in vivo formation of the vesicles. The existence of LDH-containing vesicles in enamel organ, where mineralization had been believed not to be initiated by matrix vesicles, suggests the possibility that LDH-containing vesicles have a specific function different from that of matrix vesicles.

Presence of vesicles containing lactate dehydrogenase in the dentin of bovine tooth germs

The dentin was removed from bovine tooth germs, followed by the separation of the extracellular matrix vesicle fraction after collagenase treatment. Lactate dehydrogenase (LDH)-containing vesicles with a density different from that of matrix vesicles were detected in the matrix vesicle fraction. LDH in these vesicles did not result from cell lysis and vesicle capture during the preparation of the matrix vesicle fraction. The isoenzyme pattern of LDH in LDH-containing vesicles was similar to that of cytosolic LDH of odontoblasts. Other cytosolic enzymes were not detected in LDH-containing vesicles, suggesting the presence of a mechanism for specific uptake of cytosolic LDH during the in vivo formation of the vesicles.

Intraperoxisomal form of alanine:glyoxylate aminotransferase in the peroxisomes of bird kidney

Alanine:glyoxylate aminotransferase has been reported to be present as the apo form in the peroxisomes and as the holo form in the mitochondria in chicken kidney. In contrast, the enzyme was found to be present as the holo form both in the peroxisomes and in the mitochondria in pigeon kidney, suggesting that birds are classified into two groups on the basis of intraperoxisomal form of kidney alanine:glyoxylate aminotransferase. In the kidney, the pigeon peroxisomal holo enzyme did not cross-react immunologically with the chicken peroxisomal apo enzyme.

Purification and characterization of peroxisomal apo and holo alanine:glyoxylate aminotransferase from bird liver

Alanine:glyoxylate aminotransferase has been reported to be present as the apo enzyme in the peroxisomes and as the holo enzyme in the mitochondria in chick (white leghorn) embryonic liver. However, surprisingly, birds were found to be classified into two groups on the basis of intraperoxisomal forms of liver alanine:glyoxylate aminotransferase. In the peroxisomes, the enzyme was present as the holo form in group 1 (pigeon, sparrow, Java sparrow, Australian budgerigar, canary, goose, and duck), and as the apo form in group 2 (white leghorn, bantam, pheasant, and Japanese mannikin). In the mitochondria, the enzyme was present as the holo form in both groups. The peroxisomal holo enzyme was purified from pigeon liver, and the peroxisomal apo enzyme from chicken (white leghorn) liver. The pigeon holo enzyme was composed of two identical subunits with a molecular weight of about 45,000, whereas the chicken apo enzyme was a single peptide with the same molecular weight as the subunit of the pigeon enzyme. The peroxisomal holo enzyme of pigeon liver was not immunologically cross-reactive with the peroxisomal apo enzyme of chicken liver, the mitochondrial holo enzymes from pigeon and chicken liver, and mammalian alanine:glyoxylate aminotransferases 1 and 2. The mitochondrial holo enzymes from both pigeon and chicken liver had molecular weights of about 200,000 with four identical subunits and were cross-reactive with mammalian alanine:glyoxylate aminotransferase 2 but not with mammalian alanine:glyoxylate aminotransferase 1.

Alanine:glyoxylate aminotransferase is present as the apoenzyme in the peroxisomes of chicken kidney

The subcellular distribution of alanine:glyoxylate aminotransferase in chicken kidney was examined by centrifugation in a sucrose density gradient. The enzyme was found to be present as the apoform in the peroxisomes and as the holoform in the mitochondria. Alanine:glyoxylate aminotransferase in different mammalian kidneys were all present as the holoenzyme in the mitochondrial and soluble fractions.

Intracellular predominance of the pyridoxal 5'-phosphate form of aspartate aminotransferase in Escherichia coli B and reversible transformation of this form by extracellular substances

The intracellular proportion of the pyridoxal 5'-phosphate form of aspartate aminotransferase to the total enzyme in E. coli B cells was determined by a newly devised method, dependent on selective inactivation of the intracellular pyridoxal 5'-phosphate form of the enzyme by extracellularly added sodium borohydride. A large portion (80-99%) of the intracellular aspartate aminotransferase was in pyridoxal 5'-phosphate form in both natural and synthetic medium-grown bacterial cells. The intracellular predominancy of pyridoxal 5'-phosphate did not vary during the growth of bacteria and during incubation of bacterial cells in various kinds of buffers with different pH values. In contrast, the saturation levels generally used to describe in vivo the proportions of the apo and holo vitamin B6-dependent enzymes did not reflect the intracellular amount of the pyridoxal 5'-phosphate (holo) form of aspartate aminotransferase probably because the intracellular pyridoxal 5'-phosphate form was changed to an apo form by the disruption of bacterial cells for preparing crude extract. Various extracellularly-added vitamin B6 antagonists decreased the intracellular amount of pyridoxal 5'-phosphate without decrease in the total intracellular activity of the enzyme. The modified forms were stable in E. coli B cells and reversed into pyridoxal 5'-phosphate form by incubation of the antagonist-treated cells in the buffer containing pyridoxal. The present results showed that the sodium borohydride reduction method can be used for further analysis of the in vivo interaction of pyridoxal 5'-phosphate and apoaspartate aminotransferase. The fact that about 50% of the intracellular pyridoxal 5'-phosphate form was changed to a modified form without impairment of cell growth in the presence of 4-deoxypyridoxine, and that about 50% of intracellular modified aspartate aminotransferase was reversed to pyridoxal 5'-phosphate by the removal of antagonist followed by incubation suggested that there exists characteristically 2 different fractions of pyridoxal 5'-phosphate forms of aspartate aminotransferase in E. coli cells.

How proteins get into microbodies (peroxisomes, glyoxysomes, glycosomes)

All microbody proteins studies, including one microbody membrane protein, are made on free polysomes and imported post-translationally. This holds for animal tissues, plants, and fungi. The majority of microbody protein sub-units are synthesized in a form not detectably different from mature sub-units. In five cases a larger precursor protein has been found. The position of the extra piece in this precursor is not known. In two of the five cases, processing of the precursor is not coupled to import; in the other three this remains to be determined. It is not even known whether information in the prepiece contributes to topogenesis, or serves other purposes. Microbody preparations from Neurospora, plant tissue and rat liver can take up some newly synthesized microbody proteins in vitro. In most cases uptake is inefficient. No special requirements for uptake have been established and whether a receptor is involved is not yet known. Several examples have been reported of peroxisomal enzymes with a counterpart in another cell compartment. With the exception of catalase, no direct evidence is available in any of these cases for two isoenzymes specified by the same gene. In the Zellweger syndrome, a lethal hereditary disease of man, characterized by a lack of peroxisomes, the levels of several enzymes of lipid metabolism are strongly decreased. In contrast, D-amino-acid oxidase, L-alpha-hydroxyacid oxidase and catalase levels are normal. The catalase resides in the cytosol. Since there is no separate gene for cytosolic catalase, the normal catalase levels in Zellweger cells show that some peroxisomal enzymes can mature and survive stably in the cytosol. It is possible that maturation of the peroxisomal enzyme in the cytoplasm can account for the finding of cytosolic catalase in some normal mammalian cells. The glycosomes of trypanosomes are microbodies that contain a glycolytic system. Comparison of the glycosomal phosphoglycerate kinase with its cytosolic counterpart has shown that these isoenzymes are 93% homologous in amino-acid sequence, but less than 50% homologous to the corresponding enzymes of yeast and mammals. This implies that few alterations are required to direct a protein into microbodies. This interpretation is supported by the evidence for homology between some microbody and mitochondrial isoenzymes in other organisms mentioned under point 4. The major changes of the glycosomal phosphoglycerate kinase relative to the cytosolic enzyme are a large increase in positive charge and a C-terminal extension of 20 amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)