ROLE OF PYRIDOXAL-5"-PHOSPHATE IN VITAMIN K-DEPENDENT CARBOXYLATION

Pyridoxal-5" -phosphate stimulates the vitamin K-dependent carboxylation of glutamyl residues to γ-carboxyglutamyl residues in synthetic pentapeptide substrate, but not in the endogenous substrate.     

IS LEUCINE EXCESS A FACTOR IN PELLAGRA?

A leucine supplement given to rats fed a niacin-deficient diet did not aggravate the deficiency condition.     

高效液相色谱法同时测定食品中的B族维生素

用HPLC法同时测定食品中的四种B族维生素(B_1,B_2,B_5,B_6)。实验用0.4mol/L盐酸,120℃、15psi水解样品。分析以μBondapakC18(300mm×3.9mm)为色谱柱,甲醇:重蒸水:庚烷磺酸(PIC-B_7)=30:68:2(V:V:V)为流动相,选择紫外254nm,对B_1、B_2和B_5以及荧光(EX295nm、EM395nm)对B_6的双通道检测,可得到很好的分离图形。B_1、B_2、B_5和B_6的线性范围与相关系数各为10～50ng(r=0.998),5～40ng(r=0.999),5～40ng(r=0.993),5～50ng(r=0.999),最小检出限各为5、5、2、2ng。回收率各为91.3％～102％,103％～105％,92％～100％和99％～100％。与参比实验相比,所得食物中B族维生素含量差异不大,并与食物成分表公布的数据十分接近。     

反相液相色谱法(RPLC)测定食品中维生素B_6(呲哆胺、呲哆醛、吡哆醇)

应用HPLC反相色谱法对维生素B_6(VB_6)的三种不同同系物(吡哆醇、吡哆胺、吡哆醛)进行分离测定是一种新的VB_6测定法,经充分粉碎的样品,用0.1M硫酸溶液,在120℃下水解30分钟,冷却后经离心、过滤,用ODS-C_(18)反相柱、pH2.0～2.5的硫酸溶液作流动相,在1.0ml/min的流速下,能将吡哆胺、呲哆醛、吡哆醇完全分离,并在激发波长293nm,发射波长395nm时,应用外标法定量,其回收率在99～103％,变异系数在5.0％～5.3％。实验结果表明,HPLC反相色谱法测定VB_6(吡哆胺、吡哆醛、吡哆醇)是一种快速,简便、灵敏度高,重现性好的方法。     

VITAMIN B6 DEFICIENCY IN RATS AND THE METABOLISM OF O-PHOSPHORYLETHANOLAMINE

Rats reared on a high-protein, pyridoxine-free diet showed osteoporotic bone changes in the tail and limb girdles, with an accompanying loss of O-phosphorylethanolamine (OPE) phospholyase activity of the liver and increased urinary excretion of OPE. It is suggested that OPE may influence bone metabolism by inhibiting alkaline phosphatase or by complexing with calcium ions. Administration of OPE was shown to increase urinary excretion of calcium.     

Effects of tetrahydroisoquinolines on dopa decarboxylase and pyridoxal kinase

The mechanism of the nullification of the therapeutic effects of levodopa by pyridoxine in parkinsonian patients is not known and is still a subject of much speculation. Among other suggestions, it has been proposed that pyridoxine and levodopa may form tetrahydroisoquinoline derivatives in vivo, which may in turn inhibit dopa decarboxylase or act as a false transmitter. This possibility was tested by synthesizing six tetrahydroisoquinoline derivatives and by studying their effects on dopa decarboxylase in brain homogenates. These compounds in concentrations of 50 mM did not inhibit dopa decarboxylase or pyridoxal kinase, which synthesizes pyridoxal phosphate.     

METOCLOPRAMIDE AS A DOPAMINE ANTAGONIST IN THE HEART AND GUT OF THE MOLLUSC TAPES WATLINGI

SUMMARY 1. Metoclopramide is a potent antagonist of the inhibitory response to dopamine in two isolated tissues, the electrically stimulated intestine and the spontaneous beating heart, from the mollusc Tapes watlingi.
2. Blockade by metoclopramide of dopamine receptors in the central nervous system of man may account for the relapse of patients with Parkinson's disease which occurs when metoclopramide is given during successful therapy with levodopa.     

Vitamin B6 deficiency: a potential cause of refractory seizures in adults

Objective: In children, vitamin B₆ (pyridoxine) deficiency has been described as a cause of seizures that are refractory to conventional antiepileptic medications. We describe the clinical presentation of 3 adults with refractory seizures (later diagnosed with vitamin B₆ deficiency) that resolved after pyridoxine treatment. Design: Case series. Setting: Tertiary care surgical intensive care unit. Patients: In the first case, a 54‐year‐old male with history of alcoholic cirrhosis developed new‐onset seizures refractory to phenytoin and levetiracetam 8 days after liver transplantation. In the second case, a 59‐year‐old male with hepatitis C infection developed intracranial hemorrhage and new‐onset seizures refractory to phenytoin, levetiracetam, and pentobarbital. The third patient is a 78‐year‐old male with a history of alcohol dependence who was admitted for an intraventricular bleed and developed new onset of refractory seizures. Interventions: Intravenous pyridoxine followed by oral pyridoxine. Measurement and Main Results: In all 3 cases, seizures persisted despite escalation of conventional antiepileptic medications but resolved within 2 days of pyridoxine supplementation. In each case, low serum pyridoxal 5′‐phosphate concentrations normalized with pyroxidine administration. Conclusions: Although refractory seizures caused by vitamin B₆ deficiency are rare in adults, it should be considered in critically ill adult patients with refractory seizures.     

The Function Of A Vitamin B6 Coenzyme In The Activation And Nuclear Binding Of Steroid Receptors

Pyridoxal 5'-phosphate reacts with activated cytosolic steroid-receptor complex, presumably by Schiff-base linkage, to inhibit its binding to DNA or cell nuclei. Vitamin B ₆ deficiency produces liver cytosol that has more activated glucocorticoid-receptor complex that can bind to DNA, and a more rapid rate of nuclear binding than controls.     

PHOSPHORYLASE RESPONSE TO VITAMIN B6 FEEDING

Weanling rats fed pyridoxine at levels equal to and ten times those recommended by the National Research Council accumulate extra muscle phosphorylase for at least six weeks, with reference to both age and muscle weight, but in proportion to the vitamin B₆ retained.