BCKDK regulates the TCA cycle through PDC in the absence of PDK family during embryonic development

Pyruvate dehydrogenase kinases (PDK1-4) inhibit the TCA cycle by phosphorylating pyruvate dehydrogenase complex (PDC). Here, we show that PDK family is dispensable for murine embryonic development and that BCKDK serves as a compensatory mechanism by inactivating PDC. First, we knocked out all four Pdk genes one by one. Surprisingly, Pdk total KO embryos developed and were born in expected ratios but died by postnatal day 4 because of hypoglycemia or ketoacidosis. Moreover, PDC was phosphorylated in these embryos, suggesting that another kinase compensates for PDK family. Bioinformatic analysis implicated branched-chain ketoacid dehydrogenase kinase (Bckdk), a key regulator of branched-chain amino acids (BCAAs) catabolism. Indeed, knockout of Bckdk and Pdk family led to the loss of PDC phosphorylation, an increase in PDC activity and pyruvate entry into the TCA cycle, and embryonic lethality. These findings reveal a regulatory crosstalk hardwiring BCAA and glucose catabolic pathways, which feed the TCA cycle.

Hepatic pyruvate carboxylase expression differed prior to hyperketonemia onset in transition dairy cows

Fatty acids (FA) provide an energy source to the liver during negative energy balance; however, when FA influx is excessive, FA can be stored as liver lipids or incompletely oxidized to β-hydroxybutyrate (BHB). The objectives of this study were to quantify plasma and liver FA profiles and hepatic gene expression in cows diagnosed with hyperketonemia (HYK; BHB ≥ 1.2 mM) or not (nonHYK; BHB < 1.2 mM) to determine a relationship between FA profile and expression of hepatic genes related to oxidation and gluconeogenesis. Production parameters, blood samples (-28, -3, 1, 3, 5, 7, 9, 11, and 14 d relative to parturition; n = 28 cows), and liver biopsies (1, 14, and 28 d postpartum; n = 22 cows) were collected from Holstein cows. Cows were retrospectively grouped as HYK or nonHYK based on BHB concentrations in postpartum blood samples. Average first positive test (BHB ≥ 1.2 mM) was 9 ± 5 d (± SD). Cows diagnosed with HYK had greater C18:1 and lower C18:2 plasma proportions. Liver FA proportions of C16:0 and C18:1 were related to proportions in plasma, but C18:0 and C18:2 were not. Some interactions between plasma FA and HYK on liver FA proportion suggests that there may be preferential use depending upon metabolic state. Cows diagnosed with HYK had decreased pyruvate carboxylase (PC) expression, but no difference at 1 d postpartum in either cytosolic or mitochondrial isoforms of phosphoenolpyruvate carboxykinase (PCK). The increased PC to PCK ratios in nonHYK cows suggests the potential for greater hepatic oxidative capacity, coinciding with decreased circulating BHB. Interestingly, FA, known regulators of PC expression, were not correlated with PC expression at 1 d postpartum. Taken together, these data demonstrate that HYK cows experience a decrease in the ratio of hepatic PC to PCK at 1 day postpartum prior to HYK diagnosis which, on average, manifested a week later. The differential regulation of PC involved in HYK diagnosis may not be completely due to shifts in FA profiles and warrants further investigation.

Serum paraoxonase-1 activity in tail and mammary veins of ketotic dairy cows

The objective of this study was to evaluate the association between ketonemia and serum paraoxonase-1 (PON1), malondialdehyde (MDA), and other blood components in tail and mammary veins of dairy cows. Forty-two Holstein dairy cows with decreased feed intake were divided into HIGH (≥ 1.2 mM; n = 31) and LOW (< 1.2 mM; n = 11) groups based on the β-hydroxybutyrate concentration in plasma collected from the tail vein. The HIGH group had a significantly greater plasma non-esterified fatty acid (NEFA) concentration, but significantly lower serum PON1 activity and phospholipid concentration, and a tendency to have a lower cholesterol ester concentration than the LOW group. Serum PON1 activity was not correlated with the MDA concentration but was positively correlated with serum concentrations of cholesterol esters and phospholipids, and negatively correlated with the plasma NEFA concentration. These results suggest that serum PON1 activity is reduced by hyperketonemia and the relevance of PON1 to MDA seems to not be direct, though it is involved.

Identification of IQ motif-containing GTPase-activating protein 1 as a regulator of long-term ketosis

IQ motif-containing GTPase-activating protein 1 (IQGAP1) is a ubiquitously expressed scaffolding protein that integrates multiple cellular processes, including motility, adhesion, and proliferation, but its role in metabolism is unknown. Here, we show that IQGAP1 is induced upon fasting and regulates β-oxidation of fatty acids and synthesis of ketone bodies in the liver. IQGAP1-null (Iqgap1-/-) mice exhibit reduced hepatic PPARα transcriptional activity, as evidenced during fasting, after ketogenic diet, and upon pharmacological activation. Conversely, we found that the activity of fed-state sensor mTORC1 is enhanced in Iqgap1-/- livers, but acute inhibition of mTOR in Iqgap1-/- mice was unable to rescue the defect in ketone body synthesis. However, reexpressing IQGAP1 in the livers of Iqgap1-/- mice was sufficient to promote ketone body synthesis, increase PPARα signaling, and suppress mTORC1 activity. Taken together, we uncover what we believe to be a previously unidentified role for IQGAP1 in regulating PPARα activity and ketogenesis.

Ketonuria may be associated with low serum amylase independent of body weight and glucose metabolism

CONTEXT

Ketonuria, which reflects a preferential combustion of lipids relative to carbohydrates, is often observed in lean rather than obese people. Clinical studies have shown that individuals with diabetes and/or obesity predispose to have low serum amylase (LSA).

OBJECTIVE

To investigate the association between ketonuria and LSA.

METHODS

We examined ketonuria assessed by dipstick urinalysis and clinical parameters including serum amylase in 3638 Japanese people aged 25-79 years who underwent a health-screening checkup.

RESULTS

There was an inverse relationship between body mass index (BMI) and serum amylase. The lowest serum amylase was observed in obese subjects (BMI ≥ 25.0 kg/m²) with positive ketonuria. Logistic regression analysis showed that ketonuria was significantly associated with LSA (<50 IU/L), which was not altered by the adjustments for relevant confounders including age, sex, BMI, and HbA1c.

CONCLUSIONS

Current results suggest a relative unavailability of carbohydrates for energy production in individuals with LSA.

A neonatal-onset succinyl-CoA:3-ketoacid CoA transferase (SCOT)-deficient patient with T435N and c.658-666dupAACGTGATT p.N220_I222dup mutations in the OXCT1 gene

Succinyl-CoA:3-ketoacid CoA transferase (SCOT) deficiency causes episodic ketoacidotic crises and no apparent symptoms between them. Here, we report a Japanese case of neonatal-onset SCOT deficiency. The male patient presented a severe ketoacidotic crisis, with blood pH of 7.072 and bicarbonate of 5.8 mmol/L at the age of 2 days and was successfully treated with intravenous infusion of glucose and sodium bicarbonate. He was diagnosed as SCOT deficient by enzymatic assay and mutation analysis. At the age of 7 months, he developed a second ketoacidotic crisis, with blood pH of 7.059, bicarbonate of 5.4 mmol/L, and total ketone bodies of 29.1 mmol/L. He experienced two milder ketoacidotic crises at the ages of 1 year and 7 months and 3 years and 7 months. His urinary ketone bodies usually range from negative to 1+ but sometimes show 3+ (ketostix) without any symptoms. Hence, this patient does not show permanent ketonuria, which is characteristic of typical SCOT-deficient patients. He is a compound heterozygote of c.1304C > A (T435N) and c.658-666dupAACGTGATT p.N220_I222dup. mutations in the OXCT1 gene. The T435N mutation was previously reported as one which retained significant residual activity. The latter novel mutation was revealed to retain no residual activity by transient expression analysis. Both T435N and N220_I222 lie close to the SCOT dimerization interface and are not directly connected to the active site in the tertiary structure of a human SCOT dimer. In transient expression analysis, no apparent interallelic complementation or dominant negative effects were observed. Significant residual activity from the T435N mutant allele may prevent the patient from developing permanent ketonuria.

Lecithin cholesterol acyltransferase (LCAT) activity as a predictor for ketosis and parturient haemoglobinuria in Egyptian water buffaloes

Lecithin cholesterol acyltransferase (LCAT) activity was measured in 48 Egyptian water buffaloes four weeks pre-parturient. The activity was significantly low in 37 buffaloes (77.1%). Four weeks post-partum, clinical examination revealed that 23 buffaloes had the clinical signs of ketosis (K) while 14 had the clinical signs of parturient-haemoglobinuria (PHU). Serum samples were collected from 5 buffaloes of each group (K and PHU) besides 5 clinically healthy buffaloes with normal LCAT (control). Glucose level was significantly reduced in K and PHU groups while the phosphorous (P) level was significantly reduced in PHU group compared to control. There were significant reductions in the total cholesterol, free cholesterol, triglycerides, total protein and albumin in K and PHU groups; whereas, significant increases in AST, GGT, non-esterified fatty acids (NEFA) and beta-hydroxybutyric acid (BHBA) in K and PHU groups were detected. Therefore, LCAT could be a predictor for metabolic disorders in Egyptian water buffaloes.

Direct evidence of iNOS-mediated in vivo free radical production and protein oxidation in acetone-induced ketosis

Diabetic patients frequently encounter ketosis that is characterized by the breakdown of lipids with the consequent accumulation of ketone bodies. Several studies have demonstrated that reactive species are likely to induce tissue damage in diabetes, but the role of the ketone bodies in the process has not been fully investigated. In this study, electron paramagnetic resonance (EPR) spectroscopy combined with novel spin-trapping and immunological techniques has been used to investigate in vivo free radical formation in a murine model of acetone-induced ketosis. A six-line EPR spectrum consistent with the alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone radical adduct of a carbon-centered lipid-derived radical was detected in the liver extracts. To investigate the possible enzymatic source of these radicals, inducible nitric oxide synthase (iNOS) and NADPH oxidase knockout mice were used. Free radical production was unchanged in the NADPH oxidase knockout but much decreased in the iNOS knockout mice, suggesting a role for iNOS in free radical production. Longer-term exposure to acetone revealed iNOS overexpression in the liver together with protein radical formation, which was detected by confocal microscopy and a novel immunospin-trapping method. Immunohistochemical analysis revealed enhanced lipid peroxidation and protein oxidation as a consequence of persistent free radical generation after 21 days of acetone treatment in control and NADPH oxidase knockout but not in iNOS knockout mice. Taken together, our data demonstrate that acetone administration, a model of ketosis, can lead to protein oxidation and lipid peroxidation through a free radical-dependent mechanism driven mainly by iNOS overexpression.

Carnitine palmitoyltransferase I in liver of periparturient dairy cows: effects of prepartum intake, postpartum induction of ketosis, and periparturient disorders

Thirty-five multiparous Holstein cows were used to determine the role of mitochondrial carnitine palmitoyltransferase I (CPT I) in liver on peripartal adaptations of fatty acid metabolism. From dry-off to parturition, cows were fed a diet at either ad libitum (n = 17) or restricted intake (RI, 80% of calculated requirements for net energy; n = 18). After parturition, all cows were fed a lactation diet. At 4 d in milk (DIM), cows underwent a physical examination and were classified as healthy (n = 15) or having at least one periparturient disorder (PD; n = 17). Cows in the healthy group were assigned to either a control (n = 6) group or a ketosis induction (KI; n = 9) group. Cows with periparturient disorders were assigned to a third (PDC; n = 17) group. Cows in control and PDC groups were fed for ad libitum intake. Cows in KI were fed at 50% of their respective intake at d 4 postpartum starting from 5 DIM and continuing to signs of clinical ketosis or until 14 DIM; cows then were returned to ad libitum intake. Liver was biopsied at -30 d, 1 d, at signs of clinical ketosis or 14 d, and 28 d relative to parturition. Mitochondria were isolated by differential centrifugation. Activity of CPT I was 5.4 and 7.6 nmol of palmitoylcarnitine formed per min/mg of protein for ad libitum and RI, respectively, at -30 DIM. Sensitivity of CPT I to its inhibitor, malonyl CoA, did not differ between ad libitum and RI cows. Differences in CPT I activity between ad libitum and RI were no longer significant at 1 DIM. Postpartum CPT I activity and malonyl CoA sensitivity at 1 DIM, onset of clinical ketosis or 14 DIM, and 28 DIM were not affected by prepartum intake (ad libitum vs. RI), postpartum health status (healthy vs. PD), or ketosis induction status (control vs. KI vs. PDC). Activity of CPT I was positively correlated with liver total lipid, liver triglyceride, liver triglyceride to glycogen ratio, and serum nonesterified fatty acids. Activity of CPT I and dry matter intake were not correlated. Prepartum intake affected prepartum CPT I activity but not malonyl CoA sensitivity. Neither induction of primary ketosis nor periparturient disorders greatly affected CPT I activity or sensitivity, which indicates that alterations of CPT I may not be a major factor in the etiology of primary ketosis or other periparturient disorders.

Reduction in serum lecithin:cholesterol acyltransferase activity prior to the occurrence of ketosis and milk fever in cows

Lecithin:cholesterol acyltransferase (LCAT) is the enzyme responsible for production of cholesteryl esters in plasma. The LCAT activity is reduced in cows with fatty liver developed during the nonlactating stage and those with the fatty liver-related postparturient diseases such as ketosis. The purpose of the present study was to examine whether reduced LCAT activity during the nonlactating stage could be detected before the occurrence of postparturient diseases. Sera from 24 cows were collected at approximately 10-day intervals from -48 to +14 days from parturition. Of the 24 cows, 14 were apparently healthy, whereas 7 had ketosis and 3 had milk fever at around parturition. Of the 14 healthy cows, 7 had unaltered LCAT activity during the observation period, whereas 7 showed reduced activity from -20 to +14 days. Ketosis and milk fever occurred at from -3 to +10 days, but reductions of LCAT activity in diseased cows had already been observed from days -20 to 0. These results suggest that LCAT activity is virtually unaffected during the peripartum period at least in some healthy cows and also that the reduction in LCAT activity can be detected before the occurrence of ketosis and milk fever.

Reduced activity of lecithin:cholesterol acyltransferase in the serum of cows with ketosis and left displacement of the abomasum

Lecithin:cholesterol acyltransferase (LCAT) activity was evaluated in sera from cows with ketosis and in some with left displacement of the abomasum (LDA) that occurred during early lactation. The enzyme activities of 652 +/- 214 U (mean +/- SD) in cows with ketosis (n = 6) and 683 +/- 110 U in those with LDA (n = 5) were significantly (p < 0.01) decreased compared to those in healthy normal cows (994 +/- 65 U, n = 8). Serum concentrations of free cholesterol, cholesteryl esters (CE) and phospholipids were similarly decreased in the two diseases. Cows whose LCAT activity and CE concentration were lower than the normal values were detected while in the non-lactating stage, and some of these cows had ketosis after parturition. It is suggested that evaluation of the LCAT activity and of the CE concentration during the non-lactating stage would be useful in detecting cows that are susceptible to postparturient disorders such as ketosis.

Succinyl-CoA:acetoacetate transferase deficiency: identification of a new patient with a neonatal onset and review of the literature

We describe the clinical symptoms and biochemical findings of a patient with succinyl-CoA:acetoacetate transferase deficiency who presented in the neonatal period and review the current literature on this subject. Our patient was initially suspected to have distal renal tubular acidosis, and subsequently, a fasting test revealed severe metabolic ketoacidosis with normal blood glucose after 13 h which suggest a defect in ketolysis. In his cultured skin fibroblasts succinyl-CoA:acetoacetate transferase was deficient (residual activity 15%). Treatment in the acute phase consisted of sodium bicarbonate. At the present age of 9 years, psychomotor and physical development are within normal limits.

CONCLUSION

Defects of ketolysis probably are underdiagnosed disorders and should be considered in infants and young children with persistent ketosis.

Relationship between inhibitor of extrathyroidal 5'-deiodinase activity and serum free fatty acid in children with nonthyroidal illness and acute ketosis

To clarify whether serum free fatty acid (FFA) is an inhibitor of extrathyroidal conversion (IEC) of thyroxine (T4) to thyronine (T3), we measured the concentration of FFA, IEC activity and thyroid hormones in normal subjects, acute ketotic children and children with low T3 syndrome due to nonthyroidal illness (NTI). Iodothyronine (I) 5'-deiodinase activity was assayed with reverse triiodothyronine (rT3) as substrate and liberated 125I-was measured. The IEC was determined by the inhibition of I 5'-deiodination by ether extract of sera or standard oleate solution. IEC values were represented as mM oleate. The serum concentration of FFA was 0.470 +/- 0.117 (SD) mM in 11 normal subjects, and it was significantly higher (1.242 +/- 0.248 mM; P < 0.01) in 10 acute ketotic children and in 7 samples from 6 NTI children (0.904 +/- 0.530 mM; P < 0.05). In contrast, there was no difference in IEC among three groups (normal subject, 0.451 +/- 0.069 mM; acute ketosis, 0.437 +/- 0.040 mM; NTI, 0.465 +/- 0.224 mM). No correlations were found between IEC activity and the serum FFA concentration or thyroid hormones in 28 samples from three groups. The sequential changes in serum thyroid hormones, FFA and IEC in 3 of 6 NTI children revealed no consistent relationship. Furthermore, one NTI child had significantly high IEC (> 1.000 mM) but its serum FFA (1.182 mM) was below the mean value for the acute ketotic group. These results indicate that 1) many NTI patients may bear no relation to IEC and 2) IEC may not be caused by serum FFA only but includes several factors.

Non-ketotic hyperglycinemia: a life-threatening disorder in the neonate

Non-ketotic hyperglycinemia (NKH) is a well-recognized metabolic cause of life-threatening illness in the neonate. The fundamental defect is in the glycine cleavage enzyme (GCE), which consists of four protein components. Our study revealed that the majority of NKH patients had a specific defect in P-protein (glycine decarboxylase). The primary lesion of NKH in gene level was investigated, using cDNA encoding human glycine decarboxylase. A three-base deletion; resulting in deletion of Phe756 was found in a Japanese patient with NKH. In the majority of NKH patients in Finland, where there is a high incidence of NKH, it was found to be due to a common mutation--a point mutation resulting in amino acid alternation from Ser564 to Ile564. Prenatal diagnosis is possible by determining the activity of GCE and also by DNA analysis. Recent findings suggest that the high concentrations of glycine in the brain may contribute to the pathophysiology of NKH by overactivating NMDA receptors via an action at the associated glycine modulatory site. These provide a possibility that early treatment with NMDA receptor antagonist may prevent brain damage in NKH.

Pretranslational activation of cytochrome P450IIE during ketosis induced by a high fat diet

Ethanol-inducible cytochrome P450 (P450IIE) is reported to be induced by ketosis. In the present study, the effects of a high fat diet on P450IIE induction and the relationship between ketone body concentration and P450IIE induction were studied by the following: 1) measurement of the activity of aniline hydroxylase, 2) immunoblot analysis for P450IIE protein, and 3) Northern blot analysis for P450IIE mRNA. The enzyme activities (aniline hydroxylase) in hepatic and renal microsomes were elevated about 2-3-fold by feeding with a high fat diet for 3 days. The increases in enzyme activities were also accompanied by 3-fold increases in immunoreactive P450IIE protein and its mRNA. In contrast, no differences were observed for the catalytic activities of N-alkoxyresorufin dealkylases or the amounts of immunoreactive P450IA and P450IIC, indicating a specific induction of P450IIE by high fat feeding. Furthermore, the increases in the levels of P450IIE mRNA correlated positively (r = 0.73) with plasma concentrations of acetoacetate and beta-hydroxybutyrate but not with that of acetone, which induces P450IIE without changing its mRNA level. Our data thus indicated that P450IIE induction during the ketosis of a high fat feeding appears to be due to pretranslational activation and that is similar to the induction mechanism of fasted and diabetic animals.

Acetoacetyl CoA thiolase deficiency presenting as ketotic hypoglycemia

We report two children who presented with hypoglycemia and metabolic acidosis in whom acetoacetyl-CoA thiolase (EC 2.3.1.9) measured in fibroblast homogenates was deficient. Deficiency of this enzyme is normally associated with urinary excretion of 2-methylacetoacetate and in one child the urinary excretion of 2-methylacetoacetate, 2-methyl-3-hydroxybutyrate, and tiglylglycine was raised. By contrast, in the other child, the urinary excretion of these metabolites was very low even during ketoacidosis and following an isoleucine load. We suggest that this could be due to deficiency of the extrahepatic isoenzyme, a defect that may be responsible for some of the cases of "ketotic hypoglycemia."

Mitochondrial acetoacetyl-CoA thiolase deficiency

A patient with severe progressive neuropathy and growth retardation who showed a persistent ketosis despite normal blood glucose levels is described. A liver biopsy was analyzed for 3-oxoacyl-CoA thiolase activity. One of the mitochondrial 3-oxoacyl-CoA thiolases which in normal control liver could be activated by K+ was virtually absent in the patient's liver. An intensive search for 3-methylhydroxybutyric acid and 3-methylacetoacetic acid by gas chromatography/mass spectroscopy in the patient's urine failed to show the presence of these acids, demonstrating that the 3-methylacetoacetyl-CoA thiolase is functioning in this patient. It is therefore concluded that the persistent ketosis is due to a deficiency of the mitochondrial acetoacetyl-CoA specific thiolase.

[Metabolic aspects of alcoholic liver damage: 1984/5 update. 1. Epidemiology and alcohol metabolism]

In western industrialized countries ethanol is an important etiologic factor in the development of cirrhosis of the liver. Metabolic, immunologic and physico-chemical alterations of the hepatocyte due to ethanol are involved in the pathogenesis of alcoholic liver disease. However, the mechanisms by which ethanol damages the liver are far from clear. During the last two decades, the effect of ethanol on multiple biochemical pathways of the hepatocyte has been investigated intensively. The present paper is focusing on the metabolic aspects of alcoholic liver disease. In the first part of the review, special emphasis has been led on the metabolites of ethanol oxidation, while in the second part microsomal enzyme induction due to alcohol has been discussed. More than 90% of ethanol metabolism takes place in the liver via cytoplasmic alcoholdehydrogenase (ADH) and via a microsomal ethanol oxidizing system (MEOS). The products of these reactions are reduced nicotinadenine dinucleotide phosphate (NADH), acetaldehyde and acetate. NADH alters the redox state of the liver cell favouring all reductive processes. This shift in metabolic pathways results in hyperlactacidaemia, lactacidosis, ketosis and hyperuricaemia. Disturbances of the carbohydrate metabolism may lead either to hypo- or hyperglycaemia. The altered redox state also influences the metabolic pathways of lipid metabolism leading to lipid accumulation within the hepatocyte which can be morphologically observed as alcoholic fatty liver. In addition, porphyrin and collagen metabolism is also affected by the increased NADH/NAD+ ratio. On the other hand, acetaldehyde damages the microtubular system and the mitochondria. Acetaldehyde may also be responsible for the increased lipidperoxidation after chronic ethanol ingestion.

Stimulation of ketogenesis by propionate in isolated rat hepatocytes: an explanation for ketosis associated with propionic acidaemia and methylmalonic acidaemia?

The effect of propionate on ketone body production from oleate and octanoate in isolated rat hepatocytes was studied. Propionate (5 mmol/l) stimulated ketogenesis from oleate and octanoate, although the effect was more pronounced when octanoate was used as substrate. Propionate decreased CO2 production from fatty acids, suggesting that propionate inhibited the oxidation of free fatty acid carbons through the tricarboxylic acid cycle. Our results suggest that propionate enhanced ketogenesis as a consequence of the decrease in the rate of the tricarboxylic acid cycle, caused by propionate and/or its derivatives. The stimulation of ketogenesis caused by propionate is discussed as the possible cause of ketosis associated with propionic acidaemia and methylmalonic acidaemia.

Decreased tissue guanylate cyclase activity in glycosuric Djungarian hamsters (Phodopus sungorus) that is correctable with insulin

Twelve hyperglycemic, glycosuric, and ketonuric Djungarian hamsters with average blood glucose concentrations of 295+-32 mg/dl were compared to twelve non-glycosuric, but ketonuric Djungarian hamsters with average blood glucose concentrations of 88+-11 mg/dl with regards to their cyclic nucleotide metabolism. The glycosuric Djungarian hamsters had decreased guanylate cyclase (E.C.4.6.1.2.) activity in vitro and cyclic GMP levels in vivo in liver, lung, kidney, colon, heart, spleen, and pancreas that was approximately 50% of the guanylate cyclase activity in these same tissues of non-glycosuric Djungarian hamsters. The decreased tissue guanylate cyclase activity and cyclic GMP levels in the glycosuric animals could be restored to the level of non-glycosuric Djungarian hamsters with 100 U regular insulin, but not with 50 or 10 U of regular insulin. Fifty and 100 U of regular insulin also increased the level of guanylate cyclase activity in the non-glycosuric (control) animals. There was no change in adenylate cyclase (E.C.4.6.1.1.) activity but there were increased cyclic AMP levels in the glycosuric when compared to the non-glycosuric Djungarian hamsters that were correctable with 100 U of insulin. We conclude that guanylate cyclase activity is decreased in the peripheral tissues of glycosuric Djungarian hamsters as compared to non-glycosuric Djungarian hamsters and that insulin modulates this enzyme.

Propionyl coenzyme A carboxylase deficiency presenting as non-ketotic hyperglycinaemia

A 4-month-old girl presented with myoclonic seizures and an electroencephalogram showing hypsarrhythmia. Hyperglycinuria and a cerebrospinal fluid to plasma glycine ratio of 0.2 suggested the diagnosis of non-ketotic hyperglycinaemia. Propionic acid and methyl citric acid were present in the urine, and propionyl coenzyme A carboxylase was deficient in leucocytes and fibroblasts. The ketotic and non-ketotic hyperglycinaemias cannot be differentiated by CSF: plasma glycine ratios.

Human propionyl CoA carboxylase: some properties of the partially purified enzyme in fibroblasts from controls and patients with propionic acidemia

We report some properties of propionyl CoA carboxylase (PCC) partially purified from cultured human fibroblasts obtained from controls and several patients with propionic acidemia. A series of steps (Triton X-100 treatment, high speed centrifugation, ammonium sulfate precipitation, and density gradient centrifugation) led to 100- to 300-fold purification of control enzyme. Control PCC had a molecular weight of nearly 700,000, contained biotin, demonstrated a pH optinum at 8.0-8.5, was activated by potassium, and followed Michaelis-Menten kinetics for each of its substrates. It was distinguished from acetyl CoA carboxylase immunologically as well as by differential purification. Each of seven lines from patients with propionic acidemia had clearly detectable PCC activity which was less than 5% of that in control lines. Although yields were poor and purification less extensive than in control lines, mutant PCC was enriched 2- to 40-fold by the same procedures employed for the control enzyme. Mutant enzyme had a pH optimum, ionic requirements, and substrate Km's similar to those of control PCC, but was distinctly more labile to both cold and heat. These findings suggest that the markedly reduced activity of PCC in these patients results from a mutation in the PCC structural gene locus or loci which leads to the synthesis of altered enzyme protein molecules.

Reduction of beta-galactosidase in the ketotic Chinese hamster kidney

Kidneys from normal, diabetic-nonketotic and ketotic Chinese hamsters were homogenized, fractionated and assayed for beta-glucosidase, and beta-galactosidase activities. The kidneys of the ketotic animals were enlarged but the protein content in each subcellular fraction was similar in all three groups of animals. beta-Glucosidase was found chiefly in the soluble fraction and no difference was observed in these animals. beta-Galactosidase was distributed in both cytoplasmic and particulate fractions; difference in the specific activity of beta-galactosidase between control and ketotic animals was found in nuclear, lysosomal-mitochondrial, microsomal and soluble fractions.