Selective amino acid deficiency in patients with impaired glucose tolerance and type 2 diabetes.

INTRODUCTION: Amino acids are important modulators of glucose metabolism, insulin secretion and insulin sensitivity. However, little is known about the changes in amino acid metabolism in patients with diabetes. PATIENTS AND METHODS: The circulating amino acid levels were determined in 17 patients with type 2 diabetes, 17 individuals with impaired glucose tolerance (IGT), and 14 control subjects. RESULTS: Total amino acid concentrations were 2850+/-57micromol/l in patients with type 2 diabetes, 2980+/-77micromol/l in individuals with IGT, and 2886+/-74micromol/l in control subjects (p=0.38). Patients with type 2 diabetes exhibited significant reductions in the concentrations of gamma-aminobutyric acid (GABA), arginine, glutamine and phosphoethanolamine (p<0.05), whereas valine levels were higher than in controls (p=0.008). In IGT subjects, GABA levels were reduced, while tyrosine concentrations were increased (p<0.05). The plasma levels of essential amino acids were positively related to fasting and post-challenge glucose levels, fasting C-peptide, HOMA insulin resistance and fasting glucagon levels (p<0.05). CONCLUSIONS: Total amino acid levels are similar in patients with diabetes, IGT subjects and controls, but the individual levels of several amino acids differ significantly between these groups. These alterations may contribute to the disturbances in insulin secretion and action in diabetic patients and may provide a rationale for offering specific amino acid supplementations to diabetic patients.

Amino acid malnutrition in patients with chronic pancreatitis and pancreatic carcinoma.

OBJECTIVES: Chronic pancreatitis (CP) and pancreatic cancer (CA) have been associated with intestinal malabsorption and inflammation. However, little is known about the changes in amino acid metabolism in such patients. METHODS: The circulating amino acid levels were determined in 12 patients with CP, 12 CA patients, and 12 controls. RESULTS: Total amino acid concentrations were 2850 +/- 71 micromol/L in controls, 2640 +/- 96 micromol/L in CP patients, and 2210 +/- 123 micromol/L in CA patients (P < 0.001). In CP patients, significant reductions in the concentrations of citrulline, gamma-aminobutyric acid, taurine, and aspartic acid were found (P < 0.05), whereas in CA patients, the levels of phosphoethanolamine, gamma-aminobutyric acid, aspartic acid, taurine, arginine, threonine, alanine, citrulline, and tryptophan were reduced. There was a significant inverse relationship between the total amino acid levels and the white blood cell counts (r = -0.44, P = 0.008). CONCLUSIONS: Both patients with CP and with CA exhibit alterations in amino acid levels. The mechanisms underlying these defects may involve intestinal malabsorption as well as systemic inflammation. Providing selective amino acid supplementation to such patients may minimize the excess morbidity and mortality associated with protein malnutrition.

Expression, purification and characterization of recombinant sucrose synthase 1 from Solanum tuberosum L. for carbohydrate engineering.

The gene sus1 from Solanum tuberosum L. encoding for sucrose synthase 1 was cloned into the plasmid pDR195 under the control of the PMA1 promotor. After transformation of Saccharomyces cerevisiae strain 22574d sus1 was constitutively expressed giving a specific activity of 0.3Umg(-1) protein in the crude extract. A one-step purification by Q-Sepharose resulted in an 14-fold purified enzyme preparation in 74% yield. SuSy1 was subsequently purified by immobilized metal ion affinity chromatography and characterized for its utilization in synthesizing different nucleotide sugars and sucrose analogues. The kinetic constants for the cleavage and synthesis reaction were determined: K(m) (UDP) 4microM; K(iS) (UDP) 0.11mM; K(m) (sucrose) 91.6mM; K(m) (UDP-Glc) 0.5mM; K(iS) (UDP-Glc) 2.3mM; K(m) (D-fructose) 2.1mM; K(iS) (D-fructose) 35.9mM. Different nucleoside diphosphates as well as different donor substrate were accepted as follows: UDP>dTDP>ADP>CDP>GDP in the cleavage reaction and UDP-Glc>dTDP-Glc>ADP-Glc>CDP-Glc in the synthesis reaction. SuSy1 shows also a broad acceptance of D- and L-ketoses and D- and L-aldoses. The acceptance of aldoses was deduced from the binding of the inhibitor 5-deoxy-D-fructose (K(i) 0.3mM), an analogue of the natural substrate D-fructopyranoside. The broad substrate spectrum renders SuSy1 from potato a versatile biocatalyst for carbohydrate engineering.