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J J Ohisalo

Publications and source records attributed to J J Ohisalo.

13 recordsLinked to original sources
PubMed1992

Weight loss normalizes the inhibitory effect of N6-(phenylisopropyl)adenosine on lipolysis in fat cells of massively obese human subjects.

1. Fat cells were isolated from massively obese patients at or before gastric bypass, from other patients after normalization of body weight after gastric bypass or gastroplasty (post-bypass patients) and from control subjects of a stable normal body weight. 2. The inhibition of isoprenaline-stimulated lipolysis by N6-(phenylisopropyl)adenosine in the presence of adenosine deaminase was much attenuated in cells from the massively obese patients as compared with those from normal-weight control subjects, but was normal in cells from post-bypass patients. 3. Isolated fat cells of the massively obese patients were larger (913 +/- 197 pl, mean +/- SEM) than those of the normal-weight group (437 +/- 95 pl). The volume of cells from the post-bypass patients was only 125 +/- 49 pl, although the body mass index of this group was almost exactly the same as that of the normal-weight control subjects. 4. Although epidemiological studies have suggested that genetic factors are important in the development and maintenance of obesity, these results demonstrate that the changes observed in the inhibitory regulation of lipolysis in obesity are secondary.

Adenosine Deaminase↗
PubMed1991

Attenuated adenosine-sensitivity and decreased adenosine-receptor number in adipocyte plasma membranes in human obesity.

Fat-cells were isolated from patients of body-mass indices (BMIs) ranging from 17.9 to 83.9 kg/m2. Isoprenaline-stimulated cyclic AMP accumulation in cells prepared from obese subjects as compared with normal-weight subjects, was less sensitive to inhibition by the adenosine agonist N6-(phenylisopropyl)adenosine (PIA) (P = 0.047). The inhibition of 7 beta-desacetyl-7 beta-[gamma-(N-methylpiperazino) butyryl]-forskolin-stimulated adenylate cyclase by PIA in the presence of adenosine deaminase was also much attenuated in crude plasma membranes of adipocytes prepared from massively obese patients as compared with lean controls (P = 0.0143). This difference was probably not due to different cell size, because adenylate cyclase of crude plasma membranes of large adipocytes was actually more sensitive to PIA than was adenylate cyclase of membranes of smaller fat-cells co-isolated from the same individual. The stimulatory effect of PIA on glucose uptake in the presence of adenosine deaminase was depressed in adipocytes prepared from obese subjects and correlated with BMI at r = -0.626 (P = 0.007) at 100 nM-PIA. The adenosine receptors were studied by using the adenosine antagonist 1,3-[3H]dipropyl-8-cyclopentylxanthine. The binding was rapid and proportional to protein concentration. There was no difference in the affinities of receptors in membranes of obese and normal-weight subjects; Kd values of all patients averaged 3.3 nM. Bmax values were 54 and 130 fmol/mg of protein in membranes prepared from seven obese and five control patients respectively. The Bmax values calculated per mg of protein correlated with BMI at r = -0.539 (P = 0.047). The adenosine content of adipose tissue was higher in obese than in control subjects. These results demonstrate an attenuated response of cyclic AMP accumulation, adenylate cyclase and glucose uptake to adenosine in fat-cells prepared from obese subjects, and suggest that this change is at least partly due to changes in the amount of adenosine receptors, but not their affinity. The decreased receptor number could be due to higher adenosine content. A higher adenosine concentration in adipose tissue could explain why lipolysis is inhibited in situ in obesity, and the desensitization could explain the diminished response to adenosine analogues in isolated fat-cells.

Adenosine↗
PubMed1991

Different metabolic regulation by adenosine in omental and subcutaneous adipose tissue.

Adenosine content was higher in omental adipose tissue (0.91 +/- 0.13 nmol g-1 of wet weight; mean +/- S.E.M.) than in abdominal subcutaneous adipose tissue (0.42 +/- 0.08 nmol g-1 of wet weight) in rapidly frozen surgical biopsy samples taken from ten patients undergoing elective abdominal surgery. This difference was statistically significant (P less than 0.002). The sensitivity of isoprenaline-stimulated lipolysis to inhibition by N6-(phenylisopropyl)adenosine was studied in omental and abdominal subcutaneous adipocytes isolated from nine patients. The effect of this adenosine Ri-site agonist was less pronounced in omental than in abdominal subcutaneous adipocytes which could be due to a desensitization phenomenon. This difference was statistically significant (P = 0.012). The ratio of the inhibitory guanine nucleotide binding proteins Gi1 and Gi2 to the corresponding stimulatory protein Gs was the same in plasma membranes prepared from omental and abdominal subcutaneous adipocytes. In conclusion, in omental adipose tissue, adenosine content is higher and the response to this nucleoside is less pronounced than in subcutaneous adipocytes. This difference cannot be explained by a different (Gi1 + Gi2)/Gs ratio.

Abdomen↗
PubMed1990

[Adipose tissue].

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Adipose Tissue↗
PubMed1979

Adenosine, thyroid status and regulation of lipolysis.

Adipocytes from hypothyroid rats do not respond to adrenaline with increased glycerol release. Adenosine deaminase largely restores lipolytic sensitivity. This effect is reversed by 2-deoxycoformycin, an inhibitor of the enzyme, and by N6-(phenylisopropyl)adenosine, which is not deaminated. Lipolytic response of normal cells to adrenaline is only 50% inhibited by phenylisopropyladenosine, whereas in cells from hypothyroid rats blockage is total. Inhibition of 50% was seen at 100 and 1 nM concentrations respectively. Insensitivity to adrenaline of hypothyroid-rat adipocytes can, at least partly, be explained by increased sensitivity to adenosine.

Adenosine↗
PubMed1977

Partial purification and properties of frog liver tyrosine aminotransferase.

Hepatic tyrosine aminotransferase of the frog Rana temporaria was partially purified by (NH4)2SO4 fractionation and successive chromatography on DEAE-cellulose DE-52, Ultrogel AcA-34, DEAE-cellulose DE-52 again and, finally, hydroxyapatite. During the last step, the enzyme activity separated into two fractions; traces of a third fraction were also found. The major form was purified 6000-fold to a specific activity of 200 units/mg of protein; it was about 50% pure by electrophoretic criteria. It had mol.wt. about 85 000 as determined by gel filtration on a Sephadex G-100 column. It was not activated by added pyridoxal 5'-phosphate. The enzyme was, however, inactivated by the pyridoxal phosphate reactants canaline and amino-oxyacetate. The enzyme was specific for 2-oxoglutarate as the amino group acceptor. Homogentisate inhibited the enzyme and adrenaline was an activator; both effects were seen at low concentrations of the effectors. The relationship between initial rate and tyrosine or 2-oxoglutarate concentration was abnormal and complex. Form-2 enzyme had similar or identical molecular weight, cofactor requirements, oxo acid specificity and kinetics.

Aminooxyacetic Acid↗
PubMed1977

On the inactivation of hepatic tyrosine aminotransferase.

Tyrosine aminotransferase from frog liver requires no exogenous pyridoxal-5'-phosphate for maximum activity. The cofactor cannot be removed from the enzyme by dialysis as in the case of the rat enzyme. Pyridoxal phosphate also fails to elevate frog liver tyrosine aminotransferase activity in vivo. The enzyme activity decreases rapidly after administration of cycloheximide, which indicates that its turnover is rapid. These results strongly contradict the cofactor-dependent model of enzyme degradation. Rat and frog liver tyrosine aminotransferases are stable in neutral homogenates at 37 degrees C but are rapidly inactivated after addition of cysteine in millimolar concentrations. This effect is probably due to cystine formed during the incubation. The rates of inactivation of the different subforms of the enzyme in this system were identical. No membrane-bound system is needed for the inactivation by cystine. It is possible that the denaturation occurs by sulfide exchange. Fructose and glucose lower the enzyme activity in both rat and frog liver to an equal extent. This effect is not due to instability of the enzyme activity in both rat and frog liver to an equal extent. This effect is not due to instability of the enzyme in the presence of sugars of their metabolites. Theories on the inactivation of enzymes will be discussed in the light of the present results.

Animals↗
PubMed1976

Heterogeneity of hepatic tyrosine aminotransferase. Separation of the multiple forms from rat and frog liver by isoelectric focussing and hydroxylapatite column chromatography and their partial characterization.

L-Tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5; TAT) and other enzymes that transaminate tyrosine in rat liver cytosol have been separated into four fractions by isoelectric focussing. One of the forms is probably identical to mitochondrial L-aspartate:2-oxoglutarate aminotransferase (EC 2.6.1.1.; mASAT). The other three forms have pI's of 4.72, 4.98 and 5.30 and Km values of 1.3 and 0.3 mM for tyrosine and alpha-ketoglutarate. These heat stable forms have little or no ASAT activity. Rat liver TAT is also separated into three peaks by hydroxylapatite. Each fraction gives only one peak of activity when electrofocussed separately. In the frog, three groups of peaks of TAT activity have been separated by hydroxylapatite column chromatography. The first group is connected with ASAT activity. These peaks (pI's 6.35, 6.50 and 6.90) are heat stable and have a Km value for tyrosine of 4 mM. These fractions probably represent cytoplasmic ASAT (sASAT). The second group of peaks has at least two subforms (pI's 9.0 and 9.4, Km for tyrosine 15 mM). These forms probably represent mASAT. The third group consists of three forms that resemble the major forms of rat liver TAT. These results indicate that heterogeneity is common to many aminotransferases and independent of regulation by glucocorticoids.

Animals↗
PubMed1975

Regulation of hepatic tyrosine aminotransferase in the frog Rana temporaria.

The regulation of hepatic tyrosine aminotransferase (L-tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5) in the rat has been extensively studied but little is known about the enzyme from other sources. We have studied the regulation of this enzyme in the frog Rana temporaria and in this paper we report that: 1. Cortisone acetate, adrenocorticotropic hormone and alpha-methyl-p-tyrosine, an agent known to induce hepatic tyrosine aminotransferase in the rat via activation of the pituitary-adrenal axis, have no effect on the activity of the enzyme in the frog. 2. Dibutyryl-3',5'-cyclic AMP induces the enzyme to about 2-fold. 3. Injection of tyrosine methyl ester and a protein-rich diet result in an increase in the enzyme activity. This increase is of the same order of magnitude as that caused by dibutyryl cyclic AMP. 4. Glucose significantly reduces tyrosine aminotransferase activity in frog liver. These results suggest that cyclic AMP induces the enzyme via a mechanism independent of glucocorticoids. The frog offers a model for studies on the regulation of hepatic tyrosine aminotransferase in vivo without interference from secondary effects mediated by the adrenals.

Adrenocorticotropic Hormone↗