Proline Metabolic Enzymes Research Articles

Alterations in the activities of the enzymes of proline metabolism in Ragi (Eleusine coracana) leaves during water stress

Free proline content in Ragi (Eleusine coracana) leaves increased markedly (6 to 85 fold) as the degree of water stress, created by polyethylene gylcol treatment, was prolonged There was also a marginal increase in soluble proteins in the stressed leaves as compared to that in the controls. Water stress stimulated the activities of ornithine aminotransferase and pyrroline-5-carboxylate reductase, the enzymes of proline biosynthesis and markedly inhibited the enzymes involved in proline degradation viz., proline oxidase and pyrroline-5-carboxylate dehydrogenase. These results suggest that increase in free proline content of Ragi leaves could be due to enhanced activities of the enzymes synthesizing proline but more importantly due to severe inhibition of the enzymes degrading proline. These observations establish for the first time, the pathway of proline metabolism in plants by way of detection of the activities of all the enzymes involved and also highlight the role of these enzymes in proline accumulation during water stress.

Alterations in proline metabolic enzymes with mammalian development

Through the use of specific radioisotopic assays, the activities of enzymes degrading and synthesizing proline were examined in rat liver and kidney as a function of development. Proline oxidase (PO), the enzyme converting proline to Δ 1-pyrroline-5-carboxylate (PC), undergoes 15- and eight-fold increases in liver and kidney, respectively, as rats mature from termfetal to adult life (6–12 wk). The differences are not due to enzyme inhibitors or activators, and kinetic analysis reveals the change to be one of greater tissue content of the same enzyme. Δ 1-Pyrroline-5-carboxylate dehydrogenase, which converts PC to glutamate, shows a two- to three-fold increase in both tissues, paralleling the changes in PO with development. Δ 1-Pyrroline-5-carboxylate reductase (PCR), the enzyme which catalyzes the committed step in endogenous proline formation, undergoes oppositely directed changes, such that adult levels are only 20%–25% of fetal levels in liver and kidney. PO/PCR ratios are 25- to 50-fold greater in adult central tissues than they are in fetal tissues. Thus, the central tissues of adult rats appear to function as proline utilizers, whereas those of young rats are chiefly proline formers. This difference may relate to different rates of utilization of proline for protein synthesis in young and adult rats.

THE ENZYMATIC DEFECT IN TYPE II HYPERPROLINEMIA: ABSENCE OF Δ-PYRROLINE-5-CARBOXYLIC ACID DEHYDROGENASE ACTIVITY

Type II hyperprolinemia is characterized by hyperprolinemia, iminoglycinuria and urinary excretion of o-aminobenzaldehyde (OAB) reactive material, presumably Δ1-pyrroline-5-carboxylic acid (PCA). We now report the first demonstration of the enzymatic defect responsible for this syndrome. The patient is an eleven year old female with 15x elevated plasma proline values, iminoglycinuria, and OAB reactive material in her urine. We compared the enzymes of proline metabolism in the fibroblasts of the patient with those in 3 normal fibroblast lines. All cells were grown in Eagles' MEM. PCA dehydrogenase was measured by recovering product glutamate-14C formed from precursor PCA-14C (7.2 × 10−6M). The reaction mixture also included NAD (3.7 × 10−4%) and 10-50 μgrams of fibroblast protein. Sonicates of the patient's fibroblasts had no detectable PCA dehydrogenase activity while sonicates from control fibroblast lines produced 34 ± 2 n moles/hour/mg protein. This value represents a 10x increase over the reaction blank. The activities of ornithine-δ-transaminase and PCA reductase were normal in sonicates of the patient's cells. These results demonstrate that the enzymatic defect in Type II hyperprolinemia is an absent or defective PCA dehydrogenase. This block in the proline catabolic pathway results in accumulation of PCA which is excreted or converted to proline by PCA reductase.

Influence of Proline Deficiency on Enzymes of Proline Metabolism in the Chick

Experiments were conducted to determine the effect of dietary proline on the activity of enzymes of proline metabolism. The omission of proline from the diet for young chicks was without effect on kidney arginase, proline oxidase, Δ1-pyrroline-5-carboxylic acid dehydrogenase; and kidney and liver ornithine-δ-transaminase and Δ1-pyrroline-5-carboxylic acid reductase activities. The lack of dietary proline, however, consistently increased the activity of liver Δ1-pyrroline-5-carboxylic acid dehydrogenase. It is proposed that this latter activity as assayed in vitro may represent in part the activity of an enzyme involved in the synthesis of proline from glutamic acid.