Purification and characterization of banana fruit acid phosphatase.

An acid phosphatase (APase, EC 3.1.3.2) from ripened banana (Musa cavendishii L. cv. Cavendish) fruit has been purified 1,876-fold to electrophoretic homogeneity and a final p-nitrophenylphosphate (pNPP)-hydrolyzing specific activity of 745 micromol Pi produced (mg protein)(-1) min(-1). Non-denaturing PAGE of the final preparation resolved a single protein-staining band that co-migrated with APase activity. SDS-PAGE and analytical gel filtration demonstrated that the purified enzyme exists as a 40-kDa monomer. That the enzyme is glycosylated was indicated by its tight absorption to Concanavalin A-Sepharose. Banana APase was relatively heat stable, displayed a symmetrical pH/activity profile with maximal activity at pH 5.8, and was activated 180% and 150% by 5 mM Mn2+ and Mg2+, respectively. The enzyme exhibited a broad substrate selectivity, with maximal specificity constants (Vmax/Km) obtained with pNPP, phosphoenolpyruvate, phenyl phosphate, and O-phospho-L-tyrosine. Potent inhibition by Pi, molybdate, vanadate, arsenate, and Zn2+ was observed. Putative metabolic functions of the APase are discussed in relation to maintaining significant Pi mobility during banana fruit ripening.

Purification and characterization of cytosolic pyruvate kinase from banana fruit.

Cytosolic pyruvate kinase (PK(c)) from ripened banana (Musa cavendishii L.) fruits has been purified 543-fold to electrophoretic homogeneity and a final specific activity of 59.7 micromol of pyruvate produced/min per mg of protein. SDS/PAGE and gel-filtration FPLC of the final preparation indicated that this enzyme exists as a 240 kDa homotetramer composed of subunits of 57 kDa. Although the enzyme displayed a pH optimum of 6.9, optimal efficiency in substrate utilization [in terms of V(max)/K(m) for phosphoenolpyruvate (PEP) or ADP] was equivalent at pH 6.9 and 7.5. PK(c) activity was absolutely dependent upon the presence of a bivalent and a univalent cation, with Mg(2+) and K(+) respectively fulfilling this requirement. Hyperbolic saturation kinetics were observed for the binding of PEP, ADP, Mg(2+) and K(+) (K(m) values of 0.098, 0.12, 0.27 and 0.91 mM respectively). Although the enzyme utilized UDP, IDP, GDP and CDP as alternative nucleotides, ADP was the preferred substrate. L-Glutamate and MgATP were the most effective inhibitors, whereas L-aspartate functioned as an activator by reversing the inhibition of PK(c) by L-glutamate. The allosteric features of banana PK(c) are compared with those of banana PEP carboxylase [Law and Plaxton (1995) Biochem. J. 307, 807-816]. A model is presented which highlights the roles of cytosolic pH, MgATP, L-glutamate and L-aspartate in the co-ordinate control of the PEP branchpoint in ripening bananas.

The biosynthesis and metabolism of the aspartate derived amino acids in higher plants.

The essential amino acids lysine, threonine, methionine and isoleucine are synthesised in higher plants via a common pathway starting with aspartate. The regulation of the pathway is discussed in detail, and the properties of the key enzymes described. Recent data obtained from studies of regulation at the gene level and information derived from mutant and transgenic plants are also discussed. The herbicide target enzyme acetohydroxyacid synthase involved in the synthesis of the branched chain amino acids is reviewed.

The role of the family in psychosocial adaptation to physical disabilities for African Americans.

The psychosocial adjustment of patients who are experiencing physical disabilities is examined within the context of a family ecological approach. Historical and sociocultural characteristics of African-American families are delineated and explored in terms of their potentially positive impact on the adjustment process. Four family strengths are delineated: strong kinship bonds, strong religious orientation, family role flexibility, and strong education/work ethic. The authors demonstrate how these various assets interact reciprocally in the family lives of those individuals who are disabled. Contrary to the predominant deficit theories, a fresh asset-oriented approach is provided. A model of the family adjustment process of African-American clients with disabilities is presented, and some of the important strengths of the African-American family system are examined. Finally, a family strengths model is applied to the therapeutic process.

Changes in serum creatine kinase isoenzyme activities after surgical procedures and cardioversion.

Serum activities of creatine kinase (CK) and its isoenzymes were monitored before and 16 to 20 hours after a variety of surgical procedures and cardioversion. Changes in total CK and CK MM activities in the surgical patients were consistent with the extent of trauma; changes in these activities in the cardioversion patients were more variable, ranging from -2 to 1829 U/l, and were unrelated to the applied electrical force. CK MB activity was unchanged after cystoscopy but rose moderately in 60% of patients after cholecystectomy, in 43% of patients requiring only implantation of a new pacemaker box, and in 87% of patients after implantation of an entire pacemaker system. No increase exceeded 6U/l. Fifty per cent of patients requiring cardioversion showed rises; the maximum value was 40.9 U/l.

Diarrhoea induced by migration of a pacemaker generator.

A case of intraperitoneal migration of a pacemaker generator is described. Chronic diarrhoea and abdominal discomfort were relieved by its removal.