The fact that written Japanese has no spaces between words leads to a lot of confusion for Japanese authors of English papers. There are 4 simple rules to follow:

1.	Parentheses always have a space from letters outside, and no space inside.
2.	There is no space between a numeral and %.
3.	There is always a space between a numeral and a unit of measurement.
4.	With punctuation marks (. , ; :) there is no space before, and a space after:

Example:

"Single-stranded cDNA was generated from 10 µg of RNA (preheated to 65⁰C) using 1 µg of random hexamer primer in a 50 µl reaction containing 50 mM Tris-HCl pH 8.3, 75 mM KCl, 10 mM DTT, 0.5 mM dNTP, 20 units of RNAsin (Promega), and 400 units of RT (BRL)."

"A 5-µl volume of the PCR products was resolved by 2% agarose gel electrophoresis."

Note also that there is no space between a numeral and ⁰C, and the space between pH and the numeral.