Respiration of sugars in spinach (Spinacia oleraces), maize (Zea mays), and Chlamydomonas reinhardtii F-60 chloroplasts with emphasis on the hexose kinases

Journal Article · Tue Jun 01 04:00:00 EDT 1993 · Plant Physiology; (United States)

OSTI ID:6247873

Singh, K K; Chen, C; Epstein, D K; Gibbs, M ^[1]

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1. Brandeis Univ., Waltham, MA (United States)

The role of hexokinase in carbohydrate degradation in isolated, intact chloroplasts was evaluated. This was accomplished by monitoring the evolution of [sup 14]CO[sub 2] from darkened spinach (Spinacia oleracea), maize (Zea mays) mesophyll, and Chlamydomonas reinhardtii chloroplasts externally supplied with [sup 14]C-labeled fructose, glucose, mannose, galactose, maltose, and ribose. Glucose and ribose were the preferred substrates with the Chlamydomonas and maize chloroplasts, respectively. The rate of CO[sub 2] release from fructose was about twice that from glucose in the spinach chloroplast. externally supplied ATP stimulated the rate of CO[sub 2] release. The pH optimum for CO[sub 2] release was 7.5 with ribose and fructose and 8.5 with glucose as substrates. Probing the outer membrane polypeptides of the intact spinach chloroplast with two proteases, trypsin and thermolysin, decreased [sup 14]CO[sub 2] release from glucose about 50% but had little effect when fructose was the substrate. Tryptic digestion decreased CO[sub 2] release from glucose in the Chlamydomonas chloroplast about 70%. [sup 14]CO[sub 2] evolution from [1-[sup 14]C]-glucose-6-phosphate in both chloroplasts was unaffected by treatment with trypsin. Enzymic analysis of the supernatant (stroma) of the lysed spinach chloroplast indicated a hexokinase active primarily with fructose but with some affinity for glucose. The pellet (membranal fraction) contained a hexokinase utilizing both glucose and fructose but with considerably less total activity than the stormal enzyme. Treatment with trypsin and thermolysin eliminated more than 50% of the glucokinase activity but had little effect on fructokinase activity in the spinach chloroplast. Tryptic digestion of the Chlamydomonas chloroplast resulted in a loss of about 90% of glucokinase activity. 34 refs., 2 figs., 6 tabs.

• DOE Contract Number: FG02-86ER13486
• OSTI ID: 6247873
• Journal Information: Plant Physiology; (United States), Journal Name: Plant Physiology; (United States) Vol. 102:2; ISSN 0032-0889; ISSN PLPHAY
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ALDEHYDES
ALGAE
BIOLOGICAL FUNCTIONS
BIOLOGICAL PATHWAYS
CARBOHYDRATES
CELL CONSTITUENTS
CEREALS
CHLAMYDOMONAS
CHLOROPHYCOTA
CHLOROPLASTS
DISACCHARIDES
ENZYMES
FOOD
FRUCTOSE
GALACTOSE
GLUCOSE
GRAMINEAE
HEXOKINASE
HEXOSES
KETONES
LILIOPSIDA
MAGNOLIOPHYTA
MAGNOLIOPSIDA
MAIZE
MALTOSE
MANNOSE
METABOLISM
MICROORGANISMS
MONOSACCHARIDES
OLIGOSACCHARIDES
ORGANIC COMPOUNDS
PENTOSES
PEPTIDES
PHOSPHORUS-GROUP TRANSFERASES
PHOSPHOTRANSFERASES
PLANTS
POLYPEPTIDES
PROTEINS
RIBOSE
SACCHARIDES
SPINACH
TRANSFERASES
UNICELLULAR ALGAE
VEGETABLES