Liver metabolism is influenced by hormones and nutrients. Amino acids such as glutamine or leucine induce an anabolic response, which resembles that of insulin in muscle and adipose tissue. In this work, the signalling pathways and the effects of insulin were compared to those of glutamine and leucine in isolated hepatocytes from normal and streptozotocin-diabetic rats. Glutamine increased cell volume and induced an anabolic response characterized by an activation of acetyl-CoA carboxylase (ACC), glycogen synthase (GS) and p70 ribosomal S6 kinase (p70S6K), the key enzymes in fatty acid, glycogen and protein synthesis, respectively. The effects of glutamine were independent of insulin and did not share its signalling components. Leucine, which is poorly metabolized by the liver and does not modify cell volume, activated ACC and p70S6K, and exerted a synergistic effect on the glutamine-induced activation of ACC and p70S6K.These amino acids did not affect insulin signalling. Insulin alone had no anabolic effect in hepatocytes, despite the activation of protein kinase B. Nevertheless, it enhanced the activation of ACC and p70S6K induced by leucine. However, insulin injected intravenously activated rat liver p70S6K. In hepatocytes from streptozotocin-diabetic animals, the metabolic responses to the amino acids and insulin were similar to those in normal hepatocytes. We conclude that glutamine, insulin and leucine exert different effects that are mediated by different signalling pathways, although their effects are combinatory. The anabolic effect of insulin in hepatocytes was strictly dependent on the permissive action of leucine.Keywords: insulin; amino acids; p70S6K; acetyl-CoA carboxylase (ACC); diabetic rat.In recent years, experimental evidence demonstrating the involvement of certain amino acids in the control of metabolism and signal transduction has accumulated (reviewed in [1]). A cross-talk between nutrients and cell signalling was first reported in studies of the regulation of hepatic autophagy, a process responsible for starvationinduced proteolysis [2]. Autophagy is inhibited by amino acids even in the absence of insulin. The mechanism involves phosphorylation of ribosomal protein S6 [3,4], which is implicated in the control of translation of certain mRNAs (reviewed in [5,6]). An amino-acid-dependent activation of the ribosomal protein S6 kinase (p70S6K), the Ser/Thr protein kinase responsible for S6-phosphorylation, was first reported in hepatocytes [7], and confirmed in several tissues and cultured cells where branched-chain amino acids like leucine play a predominant role in p70S6K activation [8][9][10][11][12][13][14]. Moreover, the branched-chain amino acids amplify the effect of insulin in activating p70S6K (reviewed in [15]).Apart from their inhibition of proteolysis through p70S6K activation, amino acids also control fatty acid and glycogen metabolism. In rat hepatocytes, Na + -cotransported amino acids like glutamine, alanine or proline stimulate lipogenesis by activation of acetyl-CoA carboxyla...

The proteins from Lathyrus sativus Linn. (chickling vetch or grass pea) seeds were investigated. Protein constitutes approximately 20% of the seed dry weight, >60% of which is composed by globulins and 30% by albumins. A single, 24 kDa polypeptide comprises more than half of the protein present in the albumin fraction. The globulins may be fractionated into three main components, which were named alpha-lathyrin (the major globulin), beta-lathyrin, and gamma-lathyrin. alpha-Lathyrin, with a sedimentation coefficient of approximately 18S, is composed of three main types of unglycosylated subunits (50-66 kDa), each of which produce, upon reduction, a heavy and a light polypeptide chain, by analogy with 11S. beta-Lathyrin, with a sedimentation coefficient of 13S, is composed by a relatively large number of subunits (8-66 kDa). Two major polypeptides are glycosylated and exhibit structural similarity with beta-conglutin from Lupinus albus. One of these possesses an internal disulfide bond. gamma-Lathyrin, with a sedimentation coefficient of approximately 5S, contains two interacting, unglycosylated polypeptides, with no disulfide bonds: the major 24 kDa albumin and the heavier (20 kDa) polypeptide chain of La. sativus lectin.