Guanosine enzymic preparation

Guanosine 5 -(a-D-rhamnopyranosyl pyrophosphate) (23) was shown to be a product of enzymic reduction of the mannosyl ester (17) in the presence of a plant extract93 or an enzyme preparation from an unidentified strain of Gram-negative bacteria.94,95 In the latter example, the 6-deoxy-D-talosyl ester, presumably 24, is also produced. 

Enzyme preparations that can convert a-D-mannopyranosyl or 6-deoxy-a-D-Zt/xo-hexopyranosyl-4-ulose esters of guanosine 5 -pyro-phosphate into the /3-L-fucopyranosyl ester were obtained from Aerobacter aerogenes,99 432 Escherichia coli,100 Salmonella strains,433 higher plants,92 and animal tissues.434 Further purification of these enzymes will be necessary for mechanistic studies. 

Nucleotidase occurs in certain leaves and plant seeds and has been purified from germinating barley. The enzyme hydrolyzes the 3 -phosphates of adenosine, inosine, guanosine, uridine, and cjrtidine as well as of coenzyme A. Purified enzyme preparations contain only traces of ATPase, acid phosphatase, and 5 -nucleotidase (126). 

N- 0 -methyl-N-(9-3 D-ribofuranosylpurin-6-yl)-carbamoyl]-threonine 2) 1-methylguanosine 3) 5-methyluridine, 1-methyl-guanosine, and 3-methylcytidine ( ) 4) 7-methylguanosine. Except for enzyme preparation n. 3, the other three are free of contaminating tRNA methylases. 

The D-mannose nucleotide sugars derived from 2 -deoxyguan-osine234 and inosine50,234 were prepared by using enzymes that catalyze the synthesis of guanosine 5 -(a-D-mannopyranosyl pyrophosphate). 

It has been discovered that the enzymic synthesis of cellulose is specifically activated by guanosine 5 -triphosphate in the presence of a protein factor and poly(ethyleneglycol)372 or calcium ions.373 This activation results in a dramatic increase in the rate of synthesis of the polymer. The enzyme, solubilized by treatment of membrane preparation with digitonin,373 retains its regulatory properties, and does not show any requirements in lipids for its activity. 

IMPDH) is an enzyme involved in guanosine nucleotide synthesis required for organisms to divide and replicate. Although tiazofurin, ribavirin, and mizoribine inhibit IMPDH, they exhibit broad cellular toxicity, lack of IMPDH enzyme specificity, and sustained response in monotherapy. Immunosuppressive agents with high IMPDH enzyme specificity have been prepared to address these concerns. 

GMP has been prepared from guanosine by an enzymic method, and an improved synthesis of guanosine 5 -monothiophosphate from 2, 3 -0-iso-propylideneguanosine, which avoids the need for chromatography, has been described. The pyrimidinone 7 has been converted into the 5 -phosphate 190, for use in studies of covalently-linked base pairs. Nucleotide libraries of type 191 (X = O, S) have been assembled using solid-phase techniques. The uridine-derived 5 -oxyphosphorane 191a has been prepared from the 5 -phos-phite and o-chloranil. ... 

A guanase that deaminates guanine, guanosine, 5-GMP, and azaguanine has been prepared from liver and intestine. This enzyme is rigidly specific for guanine and its derivatives, and its pH optimum is around 8. 

The N-glycosidic bonds of nucleosides and nucleotides are split by enzymes called nucleoside phosphory-lases or nucleoside hydrolases. These enzymes have been prepared from various sources, and only the properties of some of the mammalian enzymes will be considered here. A nucleoside phosphorylase purified from rat and calf liver acts on various nucleosides and nucleotides (guanosine, deoxyguanosine, and hypoxanthine) but is without effect on adenosine and xanthosine. The mechanism of the reaction is as follows ... 

A similar method is based on the enzymic hydrolysis of the yeast nucleic acid (4 ). Emulsins prepared from sweet almonds, alfalfa seeds, and many sprouted seeds hydrolyze polynucleotides (nucleic acids) to the nucleosides. Guanosine (V-ribosyl-guanine) is produced almost quantitatively and adenosine picrate (picrate of V-ribosyl-adenine) is likewise obtained in high yield. As in the earlier methods, the nucleosides are hydrolyzed by acids to give D-ribose. 

Intestinal mucosa enzyme partially inhibited by arsenate leads to the formation of guanosine, cytidine, and cytidine-5 -phosphate. This preparation splits at (2) with subsequent partial dephosphorylation. Snake venom diesterase also sphts at (2). Prostatic phosphatase liberates... 

---