The presence of indolylamine 2,3-dioxygenase was examined in human subjects by determining its activity with L-tryptophan as substrate. Enzyme activity was detected in various tissues, and was relatively high in the lung, small intestine and placenta. Human indolylamine 2,3-dioxygenase, partially purified from the placenta, had an Mr of about 40 000 by gel filtration and exhibited a single pI of 6.9. The human enzyme required a reducing system, ascorbic acid and Methylene Blue, for maximal activity and was able to oxidize D-tryptophan, 5-hydroxy-L-tryptophan as well as L-tryptophan, but kinetic studies indicated that the best substrate of the enzyme was L-tryptophan.

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SUMMARY The purpose of the present study was to investigate erythrocyte membrane abnormalities in hypertension by means of an electron spin resonance and spin-label technique. The erythrocytes from spontaneously hypertensive rats (SHR) and humans with untreated essential hypertension were examined and compared with their normotensive counterparts, and electron spin resonance spectra were obtained for a fatty spin-label agent (5-nitroxy stearate) incorporated into the erythrocyte membranes. The value of outer hyperfine splitting (2T\) was significantly higher in erythrocytes of SHR and humans with essential hypertension than in erythrocytes of normotensive controls (at 37 °C: SHR, 56.14 ± 0.51 gauss [G], n = 8; Wistar-Kyoto rats, 52.22 ±0.86 G, n = 4, p<0.01; humans with essential hypertension, 56.94 ± 0.27 G, n = 11; normotensive subjects, 55.44 ± 0.36 G, n = 8, p<0.01). The order parameter (5) was also increased in the hypertensive rats and humans compared to their respective normotensive controls. When calcium was loaded to erythrocytes with calcium ionophore A23187 (0.9 fiM) and CaCl 2 (1.0 mM), the parameters of the spectra were increased. These changes were more prominent in the hypertensive groups than in the normotensive controls. These results revealed that the erythrocyte membranes of the hypertensive subjects tolerated different spin motions than those of the normotensive controls in the electron spin resonance study and that membrane fluidity might be decreased in hypertension. Additionally, calcium loading to erythrocytes caused the reduction of membrane fluidity. Therefore, it is suggested that an abnormality of calcium handling at the cellular level might affect physical properties of the biomembranes in hypertension. 1 " 5 It seems likely that generalized abnormalities of the membranes could be involved not only in vascular smooth muscle cells but also in circulating blood cells. Erythrocytes are widely studied because they are a

Mitochondrial extracts of dog, cat, rat and mouse liver contain two forms of alanine-glyoxylate aminotransferase (EC 2.6.1.44): one, designated isoenzyme 1, has mol.wt. approx. 80 000 and predominates in dog and cat liver; the other, designated isoenzyme 2, has mol.wt. approx. 175 000 and predominates in rat and mouse liver. In rat and mouse liver, isoenzyme 1 activity was increased by the injection in vivo of glucagon, but not isoenzyme 2 activity. Isoenzyme 1 was purified and characterized from liver mitochondrial extracts of the four species. Both rat and mouse enzyme preparations catalysed transamination between a number of L-amino acids and glyoxylate, and with L-alanine as amino donor the effective amino acceptors were glyoxylate, phenylpyruvate and hydroxypyruvate. In contrast, both dog and cat enzyme preparations were specific for L-alanine and L-serine with glyoxylate, and used glyoxylate and hydroxypyruvate as effective amino acceptors with L-alanine. Evidence that isoenzyme 1 is identical with serine-pyruvate aminotransferase (EC 2.6.1.51) was obtained. Isoenzyme 2 was partially purified from mitochondrial extracts of rat and mouse liver. Both enzyme preparations were specific for L-alanine and glyoxylate. On the basis of physical properties and substrate specificity, it was concluded that isoenzyme 2 is a separate enzyme. Some other properties of isoenzymes 1 and 2 are described.

The localization and distribution of kynurenine aminotransferase (KAT), the biosynthetic enzyme of the excitatory amino acid receptor antagonist, kynurenic acid, was studied in the rat hippocampal formation with immunohistochemical methods. The enzyme was found mainly in glial cells that could be distinguished as 3 types on the basis of their shapes and locations. Typically, these cells shared the morphological features of astrocytes and exhibited glial fibrillary acidic protein immunoreactivity as demonstrated by a double-labeling technique. The distribution of KAT-containing glial cells was heterogeneous throughout the hippocampal formation. In the hippocampus, the stratum lacunosum-moleculare of Ammon's horn and the hilus contained a higher density of KAT-positive glial cells than other regions, whereas the lowest density of KAT glial cells was observed in the granule cell layer of the dentate gyrus and in the stratum radiatum of CA subfields. In the subicular complex, the density of KAT-containing glial cells was generally higher in the superficial than in the deep layer. Hippocampal neurons exhibiting KAT immunoreactivity, distinguished as nonpyramidal cells, were very few in number and mainly distributed in strata oriens and pyramidale of Ammon's horn. Substantially more KAT-positive neurons were observed in layers II and III of the subicular complex. The organization of cellular elements containing KAT may be of relevance for the function and possible dysfunction of kynurenic acid in the rat hippocampal formation.