Inhibition of phosphatidylethanolamine biosynthesis in baby hamster kidney-21 cells infected with Semliki Forest virus.

Semliki Forest virus inhibits phosphatidylethanolamine biosynthesis in baby hamster kidney-21 cells 6 h after infection. Viral infection reduced the incorporation of [1,2-14C]-ethanolamine into intact cells by approximately 50%. A similar reduction in the activity of the ethanolaminephosphotransferase (EC 2.7.8.1) was also observed. The apparent Km for CDPethanolamine was 60 muM for the microsomal enzymes from infected or mock-infected cells. In addition, exogenous diglyceride only stimulated by 1.5-fold the ethanolaminephosphotransferase from virus- or mock-infected cells, whereas the same diglyceride preparations stimulated the cholinephosphotransferase (EC 2.7.8.2) from baby hamster kidney cells by sixfold. Generation of endogenous diglyceride by pretreatment of the microsomes with phospholipase C (EC 3.1.4.3) stimulated the activity of the cholinephosphotransferase but not the ethanolaminephosphotranferase. Semliki Forest virus does not inhibit all microsomal enzymes, since the activities of NADH- K3Fe(CN)6 reductase and NADH dehydrogenase (EC 1.6.99.3) were not affected. The ethanolaminephosphotransferase from virus- and mock-infected cells showed similar profiles of activity as a function of temperature; this result and other studies suggest that that membranous environment of the ethanolaminephosphotransferase was not significantly modified by the virus.     

Comparison of the release of vasoactive factors from venous and arterial bovine cultured endothelial cells.

The release of endothelium-derived relaxing factor (EDRF), prostacyclin (PGI2), and endothelin-1 (ET-1) was measured from endothelial cells (EC) cultured from either bovine vena cava (BVCEC) or bovine aorta (BAEC). EDRF release was determined by using the superfusion bioassay technique, whereas ET-1 and PGI2 were measured by specific radioimmunoassays. Bradykinin (BK) (0.05-30 pmol) given through columns of venous or arterial EC induced a dose-dependent release of EDRF. BK (0.05 pmol) evoked a release of EDRF from venous EC that was similar to the effect of a dose of 1 pmol from arterial EC. As with BAEC, infusions of NG-monomethyl-L-arginine (30 microM) caused an inhibition of EDRF release from BVCEC that was partially reversed by coinfusions of L-arginine (L-Arg; 100 microM). BK also induced a dose-dependent release of PGI2 from BVCEC. BVCEC and BAEC produced PGI2 in equivalent amounts when arachidonic acid (9.2 and 32 pmol) was added to the Krebs' solution perfusing the cells. BVCEC and BAEC released detectable amounts of ET-1 (0.4 +/- 0.1 and 0.9 +/- 0.3 ng/mL, respectively), over a 4-h period, and the release of ET-1 was increased approximately twofold by coincubations with thrombin (0.05-1 U/mL). These findings demonstrate that venous EC have a similar capacity to arterial EC to release vasoactive factors, thus supporting the hypothesis that veins have a functional endothelium that may modulate venous tone and platelet function.     

Enzymes of myo-inositol and inositol lipid metabolism in rats with streptozotocin-induced diabetes.

Diabetes, with only mild ketosis, was induced in male rats by a single injection of streptozotocin. After 12 weeks the specific activities of enzymes concerned with the metabolism of inositol and of inositol lipids were measured in various tissues. Inositol 1-phosphate synthase (EC 5.5.1.4) was most active in testis and the activity was significantly less in diabetic rats than in controls on a similar diet. Inositol oxygenase (EC 1.13.99.1), which converts myo-inositol into glucuronic acid, was also less active in kidney from diabetic animals. CDP-diacylglycerol-inositol phosphatidyltransferase (EC 2.7.8.11) and phosphatidylinositol 4-phosphate kinase (EC 2.7.1.68) showed decreased specific activities in brain and sciatic nerve of diabetic rats. By contrast the diabetic state did not affect the specific activities of phosphatidylinositol kinase (EC 2.7.1.67) or phosphatidylinositol 4,5-bisphosphate phosphatase (EC 3.1.3.36) in these tissues. The results are discussed in relation to diabetic neuropathy.     

Epidermal cells synthesize a cytokine with interleukin 3-like properties

Interleukin 3 (IL 3) is produced by T lymphocytes and T cell lines (EL 4), as well as by a monomyelocytic cell line (WEHI 3), and it activates lymphocytes as well as mast cells. Recently we have demonstrated that epidermal cells (EC) perform monocyte/macrophage-like functions through the release of an interleukin 1-like immunomodulating mediator (EC-derived thymocyte activating factor; ETAF. Because mast cells predominantly are located in the skin, in the present study we investigated whether EC in addition to ETAF may produce IL 3. Normal as well as transformed keratinocytes were able to secrete an IL 3-like mediator (EC IL 3) that induces the proliferation of IL 3-dependent cell lines. Furthermore, both EC IL 3 and WEHI IL 3 have a similar m.w. of 30,000. In addition, an antibody against IL 3 also blocked EC IL 3 activity, suggesting that these molecules appear to be very similar. EC IL 3 production was greatly enhanced by the addition of concanavalin A, phorbol myristate acetate, lipopolysaccharide, and silica. Factor production was completely blocked by inhibiting protein synthesis. These findings demonstrate that keratinocytes synthesize an additional cytokine with the biologic and biochemical properties of IL 3, but distinct from ETAF. Thus, through the production of EC IL 3, EC may participate in the activation of mast cells and thereby mediate inflammatory as well as hypersensitivity reactions.     

Flow effects on cultured vascular endothelial and smooth muscle cell functions.

Cultured vascular endothelial cells were exposed to fluid shear stress by means of a rotary-disc shear-loading device, and the physiological effects of the conditioned medium (CM) and the homogenate (HM) of the cells on migration, adhesion and growth of endothelial cells (EC) or smooth muscle cells (SMC) were studied. Effects of shear stress on the production and secretion of collagen, one of the extracellular matrices of EC, were also studied. CM stimulated the adhesion and growth of SMC, but not of EC themselves. The ability to stimulate SMC adhesion and growth was similar in CM obtained from the static and shear-loaded cells. HM of the shear-loaded EC stimulated SMC migration. Further, HM of the shear-loaded EC contained increased amounts of collagen compared with the static EC. These results suggest that: 1) EC produce and secrete accelerators for the adhesion and growth of SMC, 2) EC react to the physical stimulus of fluid shear stress to produce stimulators of SMC migration, and 3) EC produce collagen, the production of which is enhanced by fluid shear stress.     

The effect of phospholipases on the active uptake of norepinephrine by synaptosomes isolated from the cerebral cortex of guinea pig

—Phospholipase A (EC 3.1.1.4) and phospholipase C (EC 3.1.4.3) were used for studying the role of phospholipid of synaptosomal membrane on norepinephrine uptake activity. Synaptosomes were isolated from cerebral cortex of guinea pigs and treated with phospholipase A or phospholipase C before the uptake experiments. Treatment of synaptosomes with phospholipase A has resulted in severe inhibition of norepinephrine-uptake. Under similar conditions, the activity of synaptosomal (Na + K)-ATPase (EC 3.6.1.4) was also inhibited by phospholipase A treatment whereas the activity of synaptosomal acetylcholinesterase (EC 3.1.1.8) was not affected. On the other hand, the norepinephrine-uptake was not influenced by phospholipase C treatment. The inhibition of norepinephrine-uptake after phospholipase A treatment may be due to the liberation of lyso-components of phospholipids since a low concentration of lysolecithin as well as other detergents (deoxycholate and sodium dodecyl sulphate) also inhibit the uptake activity. However, electron microscopic examination indicated that the synaptosomal particles still maintain their morphological features after phospholipase A treatment. It is possible that the active uptake of norepinephrine depends upon the fine arrangement of phospholipids present at the active sites of the synaptosomal membrane.     

Multiple carbohydrate-cleaving specificities in human acidic and neutral glycosidases.

The common identity of human acidic beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) and beta-D-xylosidase (1,4-beta-D-xylan xylohydrolase, EC 3.2.1.37) as one enzyme and that of acidic beta-D-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23), beta-D-fucosidase (no allotted EC number) and alpha-L-arabinosidase (alpha-L-arabinofuranoside arabinohydrolase, EC 3.2.1.55) as another enzyme is indicated by similar binding patterns of glycosidase activities of each enzyme to various lectins. by similar ratios between their intra- and extracellular levels in normal and I-cell fibroblasts and by their deficiencies in liver tissues from patients with Gaucher disease and GM1 gangliosidosis, respectively. A third enzyme, neutral beta-D-galactosidase, purified to homogeneity from human liver has been shown to possess all these five glycosidase activities at neutral pH. These neutral enzymic activities were not bound by any of the lectins examined and found to be reduced in liver and spleen of a patient with neutral beta-D-galactosidase deficiency. An additional form of beta-D-xylosidase with optimal activity at pH 7.4 was bound by the fucose-binding lectin from Ulex eurpaeus while no binding was observed for the acidic (pH 4.8) and neutral (pH 7.0) beta-D-xylosidase activities of the multiple glycosidase enzymes.     

Copper metabolism in the plaice, Pleuronectes platessa (L.)

Copper metabolism in a teleost, the plaice, Pleuronectes platessa (L.) from a natural environment has been studied. Distribution in the various tissues of the metal and of five key copper-dependent enzymes: ceruloplasmin EC 1.16.3.1; Superoxide dismutase EC 1.15.11; tryptophan oxygenase EC 1.13.1.12; cytochrome oxidase EC 1.9.3.1 and monoamine oxidase EC 1.4.3.4 have been determined. The copper distribution was found to be similar to that in mammals with the greatest concentrations in the brain and heart. Distribution of the copper enzymes is also similar to that found in mammals. A preliminary characterization of the copper enzymes showed that plaice cytochrome oxidase has a pH maximum 2 pH units more alkaline than the mammalian enzyme and that plaice tryptophan oxygenase is more sensitive to heat denaturation than the mammalian enzyme. The present data form a base-line against which studies on factors affecting the copper metabolism in a teleost can be assessed.     

Human endothelial cells inhibit granulocyte aggregation in vitro

Granulocyte aggregation in response to circulating or locally released inflammatory mediators may cause vascular injury. The factors that regulate the granulocyte aggregation response and prevent its occurrence are not defined. We found that primary monolayers of human endothelial cells (EC) derived from umbilical veins released products that inhibited granulocyte aggregation. When polymorphonuclear leukocytes (PMN) and EC were incubated together, the subsequent aggregation response to N-formyl-methionyl-leucyl-phenylalanine (fMLP) was inhibited by 40 to 60%, depending in part on the duration of incubation and the concentration of the agonist. Suspension of the granulocytes in albumin-containing buffer that had been rocked with EC monolayers had a similar effect, demonstrating that the EC release a soluble product that modulates the aggregation response. The fMLP concentration-response curve was shifted downward and to the right by EC. Incubation of the granulocytes with endothelial monolayers for various times indicated that the inhibition was maximal at 2 to 3 min, and the PMN responsiveness returned to control over the next 15 min. The inhibiting effect was not selectively directed against fMLP, because incubation of PMN with EC or suspending the PMN in supernatants from endothelial monolayers also inhibited aggregation stimulated by platelet-activating factor, leukotriene B4, and C5a desarg. Release of the inhibitory activity by EC was attenuated by indomethacin, suggesting that the activity is in part due to a cyclooxygenase pathway product. Prostacyclin (PGI2), an eicosanoid produced by EC via the cyclooxygenase pathway, inhibited granulocyte aggregation; however, PGI2 was much less potent as an inhibitor of PMN aggregation than of platelet aggregation. Furthermore, the concentration of PGI2 in buffer that had been incubated with EC was not sufficient to account for the magnitude of the PMN inhibition. The concentration of prostaglandin E2 (PGE2) was also insufficient to completely account for the inhibition. EC that had been treated with indomethacin or aspirin, which blocked the release of PGI2 and PGE2, retained the partial ability to release an activity that blunted granulocyte aggregation; this inhibiting activity was stable at 37 degrees C for 60 min. The results indicate that human EC have the biologic potential to modulate granulocyte aggregation stimulated by inflammatory mediators, and the activity is only partly due to PGI2 and other cyclooxygenase products of arachidonic acid.(ABSTRACT TRUNCATED AT 400 WORDS)     

Glutamate dehydrogenase and aspartate aminotransferase in Trypanosoma cruzi.

1. The cultured, epimastigote-form of Trypanosoma cruzi contains NADP-linked glutamate dehydrogenase (EC 1.4.1.4), with a molecular weight of about 280,000, similar to the enzyme from Plasmodium chabaudi and different from the enzymes from higher animal sources. 2. T. cruzi also contains aspartate aminotransferase (EC 2.6.1.1), with properties similar to those of the enzyme from mammals. 3. The concerted action of the transaminase and glutamate dehydrogenase might be responsible for the production of NH3 which characterizes the protein catabolism in T. cruzi.     

Role of CD11/CD18 in adhesion and transendothelial migration of T cells. Analysis utilizing CD18-deficient T cell clones.

The role of leukocyte function-associated Ag-1 (LFA-1) (CD11a/CD18) in T cell-endothelial cell (EC) interactions was assessed by utilizing CD11a/CD18-deficient T cell clones generated from a patient with leukocyte adhesion deficiency (LAD). The ability of these clones to bind to and migrate through monolayers of EC in vitro was compared with that of clones generated in a similar manner from normal controls. The LAD clones bound to EC to a similar extent as the controls. The contribution of other cell surface adhesion molecules was assessed with mAb blocking experiments. It was found that part of the EC binding by these CD11a/CD18-deficient clones was mediated by an interaction of very late Ag-4 (VLA-4) with vascular cell adhesion molecule-1 (VCAM-1) on the EC. In contrast to their normal ability to bind to EC, the capacity of the LAD clones to migrate through EC monolayers was significantly less than that of the control clones. This impairment in migration was not related to decreased intrinsic motility. Moreover, neither phorbol ester stimulation of the LAD clones nor IL-1 stimulation of the EC increased the capacity of the clones to migrate through EC monolayers, although binding to EC was augmented by both treatments. Only a minimal percentage of the migration of either control or LAD clones was inhibited by mAb to VLA-4 or VCAM-1. These data demonstrate that LFA-1 plays a central role in the transendothelial migration of T cells. In the absence of LFA-1, T cells retain the ability to bind to EC because of the activity of other receptor/ligand pairs, including VLA-4/VCAM-1. Finally, it is likely that, during both binding and transendothelial migration of T cells, additional cell surface molecules play a role.     

Ammonium and amino acid metabolism in excised leaves of wheat (Triticum aestivum) senescing in the dark

Several parameters of amino acid metabolism were studied in detached primary leaves of wheat (Triticum aestivum L. cv. Castell) during a 14 day incubation period in the dark. Protein loss was accompanied by a 5-fold increase in the total amount of free amino acids during the first 4 days of the incubation period with asparagine being the most important. Beyond this stage a pronounced intracellular accumulation of ammonium occured. A gradual decrease in the levels of free amino acids and ammonium at the later stages of senescence could in part be accounted for by leakage from the leaves. Additionally, some nitrogen was lost due to ammonia volatilization. The rapid decay of the glutamine synthetase (GS; EC 6.3.1.2)-glutamate synthase (Fd-GOGAT; EC 1.4.7.1) system and the fast decline of glutamate-pyruvate transaminase (GPT; EC 2.6.1.2) activity appear to be predominant features of senescence in the dark. Decreasing Fd-GOGAT activity was slightly compensated by a small and temporary increase in the activity of NADH-GOGAT (EC 1.4.1.14). Glutamateoxalocetate transaminase (GOT: EC 2.6.1.1) activity, although declining continuously, proved to be much more persistent. Changes in glutamate dehydrogenase (GDH; EC 1.4.1.3) activity closely resembled the profile of ammonium evolution in the leaves and NADP-isocitrate dehydrogenase (IDH; EC 1.1.1.42) activity revealed a temporary maximum during the period of rapid increase in GDH activity. Increased activity of GDH could also be induced by exogenous ammonium. Ammonium accumulation could, at least partly, be caused by increased asparaginase (EC 3.5.1.1) activity which accompanied the rapid conversion of asparagine to aspartic acid. Asparagine aminotransferase (EC 2.6.1.14) activity declined sharply from the beginning of the senescence period. Although the activity profile of glutaminase (EC 3.5.1.2) was similar to that of asparaginase, glutamine was of little importance quantitatively and an analogous relationship between glutamine and glutamic acid could not be detected.     

Patrilineal Background of Esophageal Cancer and Gastric Cardia Cancer Patients in a Chaoshan High-Risk Area in China

The Taihang Mountain range of north-central China, the Southern region area of Fujian province, and the Chaoshan plain of Guangdong province are 3 major regions in China well known for their high incidence of esophageal cancer (EC). These areas also exhibit high incidences of gastric cardia cancer (GCC). The ancestors of the Chaoshanese, now the major inhabitants in the Chaoshan plain, were from north-central China. We hypothesized that EC and GCC patients in Chaoshan areas share a common ancestry with Taihang Mountain patients. We analyzed 16 East Asian-specific Y-chromosome biallelic markers (single nucleotide polymorphisms; Y-SNPs) and 6 Y-chromosome short tandem repeat (Y-STR) loci in 72 EC and 48 GCC patients from Chaoshan and 49 EC and 63 GCC patients from the Taihang Mountain range. We also compared data for 32 Chaoshan Hakka people and 24 members of the aboriginal She minority who live near the Chaoshan area. Analysis was by frequency distribution and principal component, correlation and hierarchical cluster analysis of Y-SNP. Chaoshan patients were closely related to Taihang Mountain patients, even though they are geographically distant. Y-STR analysis revealed that the 4 patient groups were more closely related with each other than with other groups. Network analysis of the haplogroup O3a3c1-M117 showed a high degree of patient-specific substructure. We suggest that EC and GCC patients from these 2 areas share a similar patrilineal genetic background, which may play an important role in the genetic factor of EC and GCC in these populations.     

Characterization of monocyte adherence to human macrovascular and microvascular endothelial cells

The interaction of monocytes with cultured large vessel venous and arterial endothelial cells (EC) and with cultured microvascular EC was studied. Analysis of time-lapse microcinematographic video recordings showed that monocytes adhere rapidly to the surface of EC and subsequently remain spherical and fixed to the initial site of adherence. Some monocytes adherent to EC stretch out within 30 to 90 min and migrate over the EC surface or become stretched for about 10 to 30 min and then detach from the EC surface and move rapidly over the EC monolayer. It was shown that the interaction of monocytes with EC is dynamic, that the morphology of monocytes adherent to EC changes constantly, and that stretching of the monocytes over the surface of the EC is not an inevitable and irreversible consequence of binding. A quantitative adherence assay was developed in which both the morphology and the number of monocytes bound to EC were determined. For each type of EC the number of monocytes bound to a single EC was found to be linearly related to the number of monocytes added and was lower for smaller EC. The adherence of monocytes to venous and arterial EC followed a different time course than the adherence to capillary EC and adherence to both types of macrovascular EC was higher than adherence to microvascular EC was higher than adherence to microvascular EC. The percentage of adherent monocytes with a stretched morphology was lower when these cells were adherent to capillary EC than to both types of macrovascular EC and increased upon addition of serum. Adherence of monocytes to venous, arterial, and capillary EC was partially inhibited by mAb directed against the alpha-chain of lymphocyte function-associated Ag-1 or C3bi receptor (with mAb LM2/1, but not with mAb OKM1) and by mAb against the common beta-chain of the three leukocyte adhesion molecules. The degree of inhibition of monocyte adherence to EC by mAb against lymphocyte function-associated Ag-1 alpha and the common beta-chain was dependent on the type of EC and was higher for venous EC (57 to 70% inhibition) than for arterial (40 to 44% inhibition) and capillary (44 to 49% inhibition) EC. Inhibition of monocyte adherence obtained with anti-C3bi receptor-alpha mAb was similar for each EC type. mAb against p150, 95 did not affect adherence. None of the mAb could block binding completely; combinations of the mAb also did not result in increased inhibition of monocyte adherence to EC.     

Similar structures in gamma-carboxymuconolactone decarboxylase and beta-ketoadipate succinyl coenzyme A transferase.

gamma-Carboxymuconolactone decarboxylase (EC 4.1.1.44) and beta-ketoadipate succinyl coenzyme A transferase (EC 2.8.3.6) mediate different steps in the beta-ketoadipate pathway. Antisera prepared against the Pseudomonas putida transferase cross-reacted immunologically with the decarboxylase from the same organism. The transferase is formed by association of two nonidentical protein subunits. The NH2-terminal amino acid sequences of the two nonidentical transferase subunits resembled each other and also were similar to the NH2-terminal amino acid sequence of the decarboxylase.     

电导率作为流域水文变化指标初探

利用电导率作为主要指标, 研究了四川黑水河流域的水文特征.方差分析表明, 支流和干流上共10个样点的电导率值在采样地点间差异显著（枯水期和平水期,P＝0000）,但在时间上不具显著性差异（枯水期P＝0346,平水期P=0517）;对枯水期和平水期各样点的电导率值做配对t检验,得出两个时期的电导率值虽差异显著,但具有极其相似的动态规律（r=0973,P＝0000）,表明流域内电导率呈规律性的变化.可将电导率应用于水文时期的划分以及河流特征的标识等研究.通过计算支流电导率对邻近干流的贡献,可以推算各支流流量的贡献率.将电导率作为流域水文时空变化的特征性指标,可为深入研究河流水文变化提供更便捷的途径.     

Carnitine metabolism during prolonged exercise and recovery in humans

Lennon et al. (J. Appl. Physiol. 55: 489-495, 1983) have recently reported a large loss of muscle total carnitine (TC) after 40 min of moderate exercise. These authors have also suggested that elevations in plasma esterified carnitine (EC) were due to the release of these carnitine esters from muscle during exercise. After 10 male subjects underwent 90 min of cycle egometry we found no alteration in muscle TC from preexercise values. Plasma EC progressively increased above resting values during exercise and remained elevated above rest at 0.75 and 1.5 h into recovery. Elevations of plasma EC were largely due to a decrement in free carnitine (FC) in both conditions. Immediately postexercise the urinary fractional reabsorbsion of EC and FC were similar to that at rest. These results suggest that a net loss of TC from exercising muscle does not occur. As in other conditions marked by falling insulin concentrations, elevations in plasma EC could result from an exchange of carnitine with the hepatic carnitine pool.     

Proliferative capacity of enterochromaffin cells in guinea-pigs with experimental ileitis

Enterochromaffin (EC) cells regulate gut motility and secretion in response to luminal stimuli, via the release of serotonin (5-HT). Inflammatory bowel disease and other gastrointestinal disorders are associated with increased numbers of EC cells and 5-HT availability. Our aim was to determine whether proliferation of EC cells contributed to the hyperplasia associated with intestinal inflammation. Ileitis was induced in guinea-pigs by intraluminal injection of 2,4,6-trinitrobenzene sulphonic acid (TNBS). A single pulse of 5-bromo-2′-deoxyuridine (BrdU) was injected 1 or 24 h before the collection of tissue, 6 or 7 days after TNBS treatment. In the controls, the labelling index (percentage of BrdU-labelled EC cells) was less than 1%. Despite a significant increase in EC cells in the inflamed ileum, the labelling index was similar in the TNBS-treated animals to that of controls. An increased occurrence of EC cells in the BrdU-labelled zone accounted for the increase in EC cells in the inflamed ileum. Goblet cell numbers were also significantly increased in the inflamed ileum, indicating that cell hyperplasia was not limited to the enteroendocrine cell lineage. This study demonstrates that a small portion of EC cells retain some proliferative capacity; however, hyperplasia associated with ileitis is not attributable to the increased proliferation of EC cells and is not limited to one cell lineage. Therefore, EC cell hyperplasia most probably occurs at the level of the stem cell or recruitment from the progenitor pool. This work was supported by an operating grant from the Crohn’s and Colitis Foundation of Canada (CCFC; to Keith Sharkey and Dr. Gary Mawe, University of Vermont, USA). Keith Sharkey is an Alberta Heritage Foundation for Medical Research (AHFMR) Medical Scientist and the CCFC Chair in Inflammatory Bowel Disease Research. Jennifer O’Hara is an AHFMR graduate student.     

Cystathionine gamma-lyase of Streptomyces phaeochromogenes. The occurrence of cystathionine gamma-lyase in filamentous bacteria and its purification and characterization

Cystathionine gamma-lyase (EC 4.4.1.1) is widely distributed in actinomycetes, e.g. genera Streptomyces, Micromonospora, Micropolyspora, Mycobacterium, Nocardia, Streptosporangium, and Streptoverticillium. The enzyme was purified from Streptomyces phaeochromogenes (IFO 3105) in nine steps. After the last steps, the enzyme appeared to be homogenous by the criteria of polyacrylamide gel electrophoresis, analytical centrifugation, and double diffusion in agarose. The enzyme crystallized in the apo form with the addition of ammonium sulfate. The enzyme has a molecular weight of about 166,000 and consists of four subunits identical in molecular weight. The enzyme exhibits absorption maxima at 278 and 421 nm and contains 4 mol of pyridoxal 5'-phosphate/mol of enzyme. L-Cystathionine, L-homoserine, DL-lanthionine, L-djenkolic acid, and L-cystine are cleaved as preferred substrates by the Streptomyces enzyme. The alpha, beta-elimination reaction of L-cystathionine is also catalyzed by the enzyme at a ratio of about one-seventh of the alpha, gamma-elimination reaction. Cystathionine beta-synthase (EC 4.2.1.22) and cystathionine gamma-synthase (EC 4.2.99.9) activities were also detected in crude extracts of S. phaeochromogenes, but cystathionine beta-lyase (EC 4.4.1.8) was not. Consequently, the reverse transsulfuration pathway in actinomycetes may be similar to that in yeast and molds.